



Produced by Chris Curnow, Keith Edkins and the Online
Distributed Proofreading Team at http://www.pgdp.net (This
file was produced from images generously made available
by The Internet Archive)





MACHINERY'S REFERENCE SERIES

EACH NUMBER IS ONE UNIT IN A COMPLETE LIBRARY OF MACHINE DESIGN AND SHOP
PRACTICE REVISED AND REPUBLISHED FROM MACHINERY

NUMBER 21

MEASURING TOOLS

THIRD EDITION



CONTENTS

History and Development of Standard Measurements

Calipers, Dividers, and Surface Gages

Micrometer Measuring Instruments

Miscellaneous Measuring Tools and Gages



Copyright, 1910, The Industrial Press, Publishers of MACHINERY.

49-55 Lafayette Street, New York City

       *       *       *       *       *


CHAPTER I

HISTORY AND DEVELOPMENT OF STANDARD MEASUREMENTS[1]

While every mechanic makes use of the standards of length every day, and
uses tools graduated according to accepted standards when performing even
the smallest operation in the shop, there are comparatively few who know
the history of the development of the standard measurements of length, or
are familiar with the methods employed in transferring the measurements
from the reference standard to the working standards. We shall therefore
here give a short review of the history and development of standard
measurements of length, as abstracted from a paper read by Mr. W. A. Viall
before the Providence Association of Mechanical Engineers.

Origin of Standard Measurements

By examining the ruins of the ancients it has been found that they had
standard measurements, not in the sense in which we are now to consider
them, but the ruins show that the buildings were constructed according to
some regular unit. In many, if not all cases, the unit seems to be some
part of the human body. The "foot," it is thought, first appeared in
Greece, and the standard was traditionally said to have been received from
the foot of Hercules, and a later tradition has it that Charlemagne
established the measurement of his own foot as the standard for his
country.

Standards Previous to 1800

In England, prior to the conquest, the yard measured, according to later
investigations, 39.6 inches, but it was reduced by Henry I in 1101, to
compare with the measurement of his own arm. In 1324, under Edward II, it
was enacted that "the inch shall have length of three barley corns, round
and dry, laid end to end; twelve inches shall make one foot, and three feet
one yard." While this standard for measurement was the accepted one,
scientists were at work on a plan to establish a standard for length that
could be recovered if lost, and Huygens, a noted philosopher and scientist
of his day, suggested that the pendulum, which beats according to its
length, should be used to establish the units of measurement. In 1758
Parliament appointed a commission to investigate and compare the various
standards with that furnished by the Royal Society. The commission caused a
copy of this standard to be made, marked it "Standard Yard, 1758," and laid
it before the House of Commons. In 1742, members of the Royal Society of
England and the Royal Academy of Science of Paris agreed to exchange
standards, and two bars 42 inches long, with three feet marked off upon
them, were sent to Paris, and one of these was returned later with "Toise"
marked upon it. In 1760 a yard bar was prepared by Mr. Bird, which was
afterwards adopted as a standard, as we shall see later.

In 1774 the Royal Society offered a reward of a hundred guineas for a
method that would obtain an invariable standard, and Halton proposed a
pendulum with a moving weight upon it, so that by counting the beats when
the weight was in one position and again when in another, and then
measuring the distance between the two positions, a distance could be
defined that could at any time be duplicated. The Society paid 30 guineas
for the suggestion, and later the work was taken up by J. Whitehurst with
the result that the distance between the positions of the weight when
vibrating 42 and 84 times a minute was 59.89358 inches. The method was not
further developed.

How the Length of the Meter was Established

In 1790, Talleyrand, then Bishop of Autun, suggested to the Constituent
Assembly that the king should endeavor to have the king of England request
his parliament to appoint a commission to work in unison with one to be
appointed in France, the same to be composed of members of the Royal
Society and Royal Academy of Science, respectively, to determine the length
of a pendulum beating seconds of time. England did not respond to the
invitation, and the French commission appointed considered first of all
whether the pendulum beating seconds of time, the quadrant of the meridian,
or the quadrant of the equator should be determined as a source of the
standard. It was decided that the quadrant of the meridian should be
adopted and that 0.0000001 of it should be the standard.

The arc of about nine and one-half degrees, extending from Dunkirk on the
English Channel to Barcelona on the Mediterranean and passing through
Paris, should be the one to be measured. The actual work of measuring was
done by Mechain and Delambre according to the plans laid down by the
commission. Mechain was to measure about 25 per cent of the arc, the
southern portion of it, and Delambre the remainder; the reason for this
unequal division was that the northern division had been surveyed
previously, and the territory was well-known, whereas the southern part was
an unknown country, as far as the measurement of it went, and it was
expected that many severe difficulties would have to be surmounted. The
Revolution was in progress, and it was soon found that the perils attending
the measurement of the northern part were greater than those attending the
southern part of the territory. The people looked askance at all things
that they did not understand, and Delambre with his instruments was looked
upon as one sent to further enthrall them. He was set upon by the people at
various times and although the authorities endeavored to protect him, it
was only by his own bravery and tact that he was able to do his work and
save his life. The Committee of Safety ordered that Mechain and Delambre
close their work in 1795, and it was some time afterward before it was
resumed.

Having completed the field work, the results of their labors were laid
before a commission composed of members of the National Institute and
learned men from other nations, who had accepted the invitation that had
been extended to them, and after carefully reviewing and calculating the
work, the length of the meridian was determined, and from it was
established the meter as we now have it. A platinum bar was made according
to the figures given, and this furnishes the prototype of the meter of the
present time. Notwithstanding all of the care taken in establishing the
meter, from work done by Gen. Schubert, of Russia, and Capt. Clarke, of
England, it has been shown that it is not 0.0000001 of the quadrant passing
through Paris, but of the one passing through New York.

The Standard Yard in England--Its Loss and Restoration

Whether incited by the work of the French or not, we do not know, but in
the early part of this century the English began to do more work upon the
establishment of a standard, and in 1816 a commission was appointed by the
crown to examine and report upon the standard of length. Capt. Kater made a
long series of careful observations determining the second pendulum to be
39.1386 inches when reduced to the level of the sea. This measurement was
made on a scale made by Troughton--who, by the way, was the first to
introduce the use of the microscope in making measurements--under the
direction of and for Sir Geo. Schuckburgh. In 1822, having made three
reports, after many tests, it was recommended that the standard prepared by
Bird in 1760, marked "Standard Yard, 1760," be adopted as the standard for
Great Britain.

The act of June, 1824, after declaring that this measure should be adopted
as the standard, reads in Sec. III.: "And whereas it is expedient that the
Standard Yard, if lost, destroyed, defaced or otherwise injured should be
restored to the same length by reference to some invariable natural
Standard; and whereas it has been ascertained by the Commissioners
appointed by His Majesty to inquire into the Subjects of Weights and
Measures, that the Yard, hereby declared to be the Imperial Standard Yard,
when compared with a Pendulum vibrating Seconds of Mean Time in the
latitude of London, in a Vacuum at the Level of the Sea, is in the
proportion of Thirty-six Inches to Thirty-nine Inches and one thousand
three hundred and ninety-three ten thousandth parts of an Inch; Be it
enacted and declared, that if at any Time hereafter the said Imperial
Standard Yard shall be lost, or shall be in any manner destroyed, defaced
or otherwise injured, it shall and may be restored by making a new Standard
Yard bearing the same proportion to such Pendulum, as aforesaid, as the
said Imperial Standard Yard bears to such Pendulum."

It was not long after this act had been passed, if indeed not before, that
it became known that the pendulum method was an incorrect one, as it was
found that errors had occurred in reducing the length obtained to that at
the sea level, and despite the great pains that had been taken, it is
doubtful if the method was not faulty in some of its other details.

When the Houses of Parliament were burned in 1834, an opportunity was
offered to try the method upon which so much time and care had been spent.
A commission was appointed and to Sir Francis Baily was assigned the task
of restoring the standard. He did not live to complete the task, dying in
1844. He succeeded in determining the composition of the metal that was
best adapted to be used, which metal is now known as Baily's metal.

Rev. R. Sheepshanks constructed a working model as a standard and compared
it with two Schuckburg's scales, the yard of the Royal Society, and two
iron bars that had been used in the ordnance department. Having determined
to his own satisfaction and that of his associates the value of the yard,
he prepared the standard imperial yard, known as Bronze No. 1, a bronze bar
38 x 1 x 1 inch, with two gold plugs dropped into holes so that the surface
of the plugs passes through the center plane of the bar. Upon these plugs
are three transverse lines and two longitudinal lines, the yard being the
distance from the middle transverse line--the portion lying between the two
longitudinal ones--of one plug, to the corresponding line on the other
plug. Forty copies were made, but two of these being correct at 62 degrees
Fahrenheit, and these two, together with the original and one other, are
kept in England as the standards for reference. In 1855 the standard as
made by Rev. Sheepshanks was legalized.

Attempts to Fix a Standard in the United States

The Constitution empowers Congress to fix the standards of weights and
measures, but up to 1866 no legal standard length had been adopted. In his
first message to Congress Washington said: "A uniformity in the weights and
measures of the country is among the important objects submitted to you by
the Constitution, and if it can be derived from a standard at once
invariable and universal, it must be no less honorable to the public
council than conducive to the public convenience."

In July, 1790, Thomas Jefferson, then Secretary of State, sent a report to
Congress containing two plans, both based on the length of the pendulum, in
this case the pendulum to be a plain bar, the one plan to use the system
then existing, referring it to the pendulum as the basis, and the other to
take the pendulum and subdivide it, one-third of the pendulum to be called
a foot. The whole length was that of one beating seconds of time. He made a
table to read as follows:

  10 Points make a Line.
  10 Lines make a Foot.
  10 Feet make a Decad.
  10 Decads make a Rood.
  10 Roods make a Furlong.
  10 Furlongs make a Mile.

Congress did not adopt his system, and as England was then working on the
problem, it was decided to await the results of its labors. In 1816,
Madison, in his inaugural address, brought the matter of standards to the
attention of Congress, and a committee of the House made a report
recommending the first plan of Jefferson, but the report was not acted
upon. In 1821, J. Q. Adams, then Secretary of State, made a long and
exhaustive report in which he favored the metric system, but still advised
Congress to wait, and Congress--waited.

What the Standards are in the United States

The standard of length which had generally been accepted as _the_ standard,
was a brass scale 82 inches long, prepared by Troughton for the Coast
Survey of the United States. The yard used was the 36 inches between the
27th and 63d inch of the scale. In 1856, however "Bronze No. 11" was
presented to the United States by the British government. This is a
duplicate of the No. 1 Bronze mentioned before, which is the legalized
standard yard in England. It is standard length at 61.79 degrees F., and is
the accepted standard in the United States. A bar of Low Moor iron, No. 57,
was sent at the same time, and this is correct in length at 62.58 degrees
F. The expansion of Bronze No. 11 is 0.000342 inch, and that of the iron
bar is 0.000221 inch for each degree Fahrenheit. While the yard is the
commonly accepted standard in this country, it is not the legal standard.
In 1866 Congress passed a law making legal the meter, the first and only
measure of length that has been legalized by our government. Copies of the
meter and kilogram, taken from the original platinum bar at Paris, referred
to before, were received in this country by the President and members of
the Cabinet, on Jan. 2, 1890, and were deposited with the Coast Survey. By
formal order of the Secretary of the Treasury, April 5, 1893, these were
denominated the "Fundamental Standards."

The International Bureau of Weights and Measures

After the original meter was established, it was found that copies made by
various countries differed to a greater or less extent from the original,
and believing that a copy could be made from which other copies could be
more readily made than from the end piece meter, and that better provision
could be made for the preservation of the standard, France called a
convention of representatives from various States using the system, to
consider the matter. The United States representatives, or commissioners,
were Messrs. Henry and Hildegard, who met with the general commission in
1870. The commissioners at once set at work to solve the problem presented
to them, but the Franco-Prussian war put an end to their deliberations. The
deliberations were resumed later, and May 20, 1875, representatives of the
various countries signed a treaty providing for the establishment and
maintenance, at the common expense of the contracting nations, of a
"scientific and permanent international bureau of weights and measures, the
location of which should be Paris, to be conducted by a general conference
for weights and measures, to be composed of the delegates of all the
contracting governments."

This bureau is empowered to construct and preserve the international
standards, to distribute copies of the same to the several countries, and
also to discuss and initiate measures necessary for the determination of
the metric system. The commission adopted a form for the standard as shown
in Fig. 1. The lines representing the length of the meter are drawn on the
plane _A_, which is the neutral plane, and will not change in length should
the bar deflect. The bar is made of 90 per cent platinum and 10 per cent
iridium, about 250 kilograms having been melted when preparations were made
for the first standard, so that all of the copies made from this cast
represent the same coefficient of expansion and are subject to the same
changes as the original. The French government presented to the bureau the
pavilion Breteuil, opposite the Park of St. Cloud, which was accepted and
put into order and is now the repository of the originals of the meter and
the kilogram. The expense attending the first establishment of the bureau
was about $10,000 to the United States, and since then its share of the
annual expense has been about $900. The standards in the possession of the
United States were received through the international bureau.

The Commercial Value of a Standard

Having at the disposal of the nation a standard of length, the question
arises, "What can be made of it commercially, and how do we know when we
have a copy of the standard?"

[Illustration: Fig. 1. Form of Bar Adopted for International Standards of
Length]

In 1893, the Brown & Sharpe Mfg. Co. decided to make a new standard to
replace the one they had at that date. Mr. O. J. Beale was detailed to do
this work. He prepared steel bars about 40 inches long by 1-1/4 inch
square, and after planing them, they were allowed to rest for several
months. At the ends of these bars he inserted two gold plugs, the centers
of which were about 36 inches apart, and a little beyond these two others
about one meter apart. A bar was placed in position upon a heavy bed. This
was so arranged that a tool carrier could be passed over the bar. The tool
carrier consisted of a light framework, holding the marking tool. One
feature of the marking was that the point of the marking tool was curved
and had an angle, so that if dropped it made an impression in the form of
an ellipse. In graduations, ordinarily, the line, when highly magnified, is
apt to present at its ends an impression less definite than in the center,
by reason of the form of the objective. The line made with the tool
mentioned is short, and that portion of the line is read which passes,
apparently, through the straight line in the eye-glass of the microscope.
In order to make these lines as definite as possible, the point was lapped
to a bright surface. After being placed in position, the microscope, which
could be placed on the front of the tool carrier, was set to compare with
the graduation on the standard bar from which the new bar was to be
prepared. After such a setting the readings were made by three persons, and
by turning the lever the marking tool was dropped, making a very fine line,
so fine indeed, that when the authorities in Washington began the
examination of the bar later on they declared that no line had been made
upon these studs.

After making the first line, the carriage was moved along to compare with
the other line on the standard, and after the correction had been made by
the use of the micrometer in the microscope, the marking tool was again
dropped, giving the second line, which was intended to mark the limit of
one yard over-all. The same operation was repeated in the marking of the
meter. The whole of this work was done, of course, with the greatest care,
and, while the theoretical portion of it appears very simple in detail, it
required a great deal of time and patience before the last line had been
made. The bar thus marked was taken to Washington, and in Mr. Beale's
presence was compared by the attendants with Bronze No. 11 and later with
Low Moor bar, No. 57.

In comparing this standard, a method was employed very similar to that used
in marking it. The bar, properly supported, was placed upon a box that
rested upon rolls, and on this same box was placed the government standard
with which the Brown & Sharpe standard was to be compared. The standard was
placed in position under the microscope, and after being properly set to
the standard, the bar to be measured was placed under the microscope, and
by the micrometer screw of the microscope the variation was measured. Three
comparisons were made by each of the attendants on each end before
determining the reading of the microscope, and after such comparisons and
many repetitions of it, the value of the standard No. 2 was found to be
36.00061 inches for the yard, and 1.0000147 meter for the meter.

After this work had been done, Mr. Beale prepared a second standard which
he called No. 3, and after examining, as shown above, the error was found
to be 0.00002 inch for the yard, and 0.000005 meter for the meter.
Observing these variations as compared with the standards originally made,
we find they are very close, and it is doubtful if many repeated trials
would furnish more accurate work, when we remember that out of forty
original standards made, but two are correct at 62 degrees Fahrenheit.

After establishing a yard, the problem of obtaining an inch comes next, and
this was made by subdividing the yard into two equal parts, these into
three, and the three further subdivided into six parts. It should be
particularly noted that no mention has been made of a standard inch, as
there is none, the standard yard only existing, the subdivision of which
falls upon those undertaking standard work. There is a remarkable agreement
between at least three leading gage makers of this country and abroad, and
each came to the result by its own method of subdividing the standard yard.

Kinds of Measurements and Measuring Tools

The measurements in the shop may, in general, be divided into measurements
of length and measurements of angles. The length measurements in turn may
be divided into line measurements and end measurements, the former being
made by placing a rule or similar instrument against the object being
measured, and comparing its length with the graduations on the measuring
instruments; the latter are made by comparing the object being measured
with the measuring instrument, by bringing the object measured into actual
contact with the measuring surfaces of the instrument. Examples of line
measurements are the ordinary measurements made with the machinist's rule,
and examples of end measurement are those made by the micrometer, measuring
machines, and snap gages. Angular measurements can also be divided into two
classes; those measured directly by graduations on the instrument, and
those measured by comparison with a given angle of the instrument.

Measuring instruments may also be divided into two classes, according to
whether they actually are used for measuring, or whether they are
principally used for comparing objects with one another. According to this
classification all kinds of rules and protractors belong to the first
class, whereas all gages belong to the second class. The ordinary
instruments for length measurements, the regular machinists' rule, the
caliper square, and the ordinary micrometer caliper, are too well known to
require any additional explanation. The same is true of the regular bevel
protractor for measuring angles. We shall therefore in the following
chapters deal principally with special measuring tools, and with such
methods in the use of tools which are likely to suggest improvements, or
otherwise be valuable to the user and maker of measuring tools.

       *       *       *       *       *


CHAPTER II

CALIPERS, DIVIDERS, AND SURFACE GAGES

In the present chapter we shall deal with the simpler forms of tools used
for measuring, such as ordinary calipers, and their use; surface gages;
special attachments for scales and squares, facilitating accurate
measuring; and vernier and beam calipers. The descriptions of the tools and
methods referred to have appeared in MACHINERY from time to time. The names
of the persons who originally contributed these descriptions have been
stated in notes at the foot of the pages, together with the month and year
when their contribution appeared.

Setting Inside Calipers

[Illustration: Figs. 2 and 3 - Fig. 4 - Setting Inside Calipers]

It is customary with most machinists, when setting inside calipers to a
scale, to place one end of the scale squarely against the face of some true
surface, and then, placing one leg of the caliper against the same surface,
to set the other leg to the required measurement on the scale. For this
purpose the faceplate of the lathe is frequently used on account of its
being close at hand for the latheman. The sides of the jaws of a vise or
almost anything located where the light is sufficient to read the markings
on the scale are frequently used.

The disadvantages of this method are, first, that a rough or untrue object
is often chosen, particularly if it happens to be in a better light than a
smooth and true one, and, second, that it is very hard to hold the scale
squarely against an object. It is easy enough to hold it squarely
crosswise, but it is not so easy a matter to keep it square edgewise. As
can be readily seen, this makes quite a difference with the reading of the
calipers, particularly if the scale is a thick one.

Figs. 2 and 3 show this effect exaggerated. _B_ is the block against which
the scale abuts. The dotted line indicates where the caliper leg should
rest, but cannot do so, unless the scale is held perfectly square with the
block. Fig. 4 shows a method of setting the calipers by using a small
square to abut the scale and to afford a surface against which to place the
leg of the caliper. The scale, lying flat on the blade of the square, is
always sure to be square edgewise, and is easily held squarely against the
stock of the square as shown. This method has also the advantage of being
portable, and can be taken to the window or to any place where the light is
satisfactory. When using a long scale, the free end may be held against the
body to assist in holding it in place.[2]

Shoulder Calipers

[Illustration: Fig. 5. Shoulder Calipers]

In Fig. 5 are shown a pair of calipers which are very handy in measuring
work from shoulder to shoulder or from a shoulder to the end of the piece
of work. For this purpose they are much handier, and more accurate, than
the ordinary "hermaphrodites." The legs are bent at _AA_ so as to lie flat
and thus bring the point of the long leg directly behind the short one
which "nests" into it, as at _B_, so that the calipers may be used for
short measurements as well as for long ones.

Double-jointed Calipers to Fold in Tool Box

In Fig. 6 are illustrated a pair of large calipers that can be folded up
and put in a machinist's ordinary size tool chest. The usual large caliper
supplied by the average machine shop is so cumbersome and heavy that this
one was designed to fill its place. It can be carried in the chest when the
usual style of large caliper cannot. It is a very light and compact tool.
It is a 26-inch caliper, and will caliper up to 34 inches diameter. The top
sections are made in four pieces, and the point ends fit between the top
half like the blade of a knife, as shown in the engraving. Each side of the
upper or top section is made of saw steel 1/16 inch thick, and the lower
part or point of steel 1/8 inch thick. The double section makes the tool
very stiff and light.

The point section has a tongue _A_, extending between the double section,
which is engaged by a sliding stud and thumb nut. The stud is a nice
sliding fit in the slot, and the thumb nut clamps it firmly in place when
in use. _B_, in the figure, shows the construction of the thumb nut. _C_ is
a sheet copper liner put between the washers at _A_. The dotted lines in
the engraving show the points folded back to close up. The large joint
washers are 1-3/4 inch diameter, and a 5/8-inch pin with a 3/8-inch hexagon
head screw tightens it up. The forward joints are the same style, but
smaller. The main joint has two 1-3/4-inch brass distance pieces or washers
between the two main washers. The top section is 12-1/2 inches between
centers, and the point sections 15 inches from center to point. Closed up,
the calipers measure 16 inches over-all.

[Illustration: Fig. 6. Large Double-jointed Calipers]

Kinks in Inside Calipering

Close measurements may be made by filing two notches in each leg of an
inside caliper so as to leave a rounded projection between, as shown at
_E_, Fig. 7. Then, with an outside caliper, _D_, the setting of the inside
caliper, _B_, is taken from the rounded points. The inside caliper can be
reset very accurately after removal by this method. A still better way is
to have two short pins, _CC'_ set in the sides of the inside caliper legs,
but this is not readily done as a makeshift. To measure the inside diameter
of a bore having a shoulder like the piece _H_, the inside caliper _F_ may
also be set as usual and then a line marked with a sharp scriber on one
leg, by drawing it along the side _G_. Then the legs are closed to remove
the caliper, and are reset to the scribed line. Of course, this method is
not as accurate as the previous one, and can be used only for approximate
measurements.

[Illustration: Fig. 7. Methods of Inside Calipering]

To get the thickness of a wall beyond a shoulder, as at _K_, Fig. 7, set
the caliper so that the legs will pass over the shoulder freely, and with a
scale measure the distance between the outside leg and the outside of the
piece. Then remove the caliper and measure the distance between the caliper
points. The difference between these two distances will be the thickness
_M_.

Inside Calipers for Close Spaces

In Fig. 8 are shown a pair of inside calipers which are bent so as to be
well adapted for calipering distances difficult of access, such as the
keyway in a shaft and hub which does not extend beyond the hub, as
indicated. With the ordinary inside calipers, having straight legs, and
which are commonly used for inside work, it is generally impossible to get
the exact size, as the end which is held in the hand comes in contact with
the shaft before both points come into the same vertical plane. The
engraving plainly shows how calipers for this purpose are made, and how
used. Any mechanic can easily bend a common pair to about the shape shown
to accommodate this class of work.[3]

[Illustration: Fig. 8. Inside Calipers for Close Spaces]

Surface Gage with Two Pointers

Figs. 9 and 10 show a special surface gage, and illustrate an original idea
which has been found to be a great saver of time and of milling cutters. It
can also be used on the planer or shaper. By its use the operator can raise
the milling machine table to the right height without testing the cut two
or three times, and eliminate the danger of taking a cut that is liable to
break the cutter. This tool is especially valuable on castings, as raising
the table and allowing the cutter to revolve in the gritty surface while
finding the lowest spot is very disastrous to the cutting edges.

[Illustration: 10]

To use this surface gage, the pointer marked _C_ in Fig. 9 is set to the
lowest spot in the casting, and then the pointer _B_ is set from it with
perhaps 1/32 inch between the points for a cut sufficient to clean up the
surface. Pointer _C_ is then folded up as shown at _C'_ in Fig. 10, and the
table is raised until the pointer _B_ will just touch the under side of the
cutter as shown at _B'_ in Fig. 10. In this way the table is quickly
adjusted to a cut that will clean the casting or other piece being
machined, and with no cutting or trying whatever.[4]

To Adjust the Needle of a Surface Gage

[Illustration: Fig. 11. Method of Adjusting the Needle of a Surface Gage]

[Illustration: Fig. 12. Scale Attachment for the Square]

Fig. 11 illustrates a method of adjusting the needle of a surface gage. To
set the gage 3-3/4 inches from the table, get somewhere within 1/4 inch of
the mark on the square. With the thumb and forefinger on hook _A_, turn the
needle till it reaches the point desired. By turning the needle, it will
travel in a circular path, on account of the bend near the point, and thus
reach the desired setting.

Scale Attachment for the Square

Fig. 12 shows a device for attaching a scale to a square. This combination
makes a very convenient tool to use when setting up work for keyseating, as
is illustrated in the engraving, in which _S_ is the shaft to be splined
and _C_ the milling cutter. It is also a very handy tool for truing up work
on the boring mill or lathe. At the upper left-hand corner, is shown the
construction of the parts, which are made of dimensions to suit the size of
the scale and the square. For the combination to be successful, it is
essential that the blade of the square is the same thickness as the
scale.[5]

Attachment for Machinist's Scale

[Illustration: Fig. 13. Convenient Attachment for Machinist's Scale]

Fig. 13 shows a very convenient appliance. It will be found very useful in
the machine shop for setting inside calipers to any desired size. The gage
is clamped over the rule wherever desired, and one leg of the calipers set
against the gage, the other leg being brought flush with the end of the
scale.[6]

Setting Dividers Accurately

To set dividers accurately, take a 1-inch micrometer and cut a line
entirely around the thimble as at _A_, Fig. 14, and then, with the
instrument set at zero, make a punch mark _B_ exactly one inch from the
line on the thimble. If less than one inch is wanted, open out the
micrometer and set the dividers to the dot and line so as to give one inch
more than the distance wanted. Now with the dividers make two marks across
a line, as at _a_ and _b_, Fig. 14, and then set the dividers to one inch
and mark another line as at c. The distance from _c_ to _b_ is the amount
desired, and the dividers can be set to it. Great care must, of course, be
exercised, if accurate results are required.

[Illustration: Fig. 14. Method of Setting Dividers Accurately]

Combination Caliper and Divider

The combination caliper and divider shown in Fig. 15 is one that is not
manufactured by any of the various tool companies. It is, however, one of
the handiest tools that can be in a machinist's kit, as it lends itself to
so many varied uses, and often is capable of being used where only a
special tool can be employed. The illustration suggests its usefulness. The
tool can be used as an outside caliper, as an inside caliper, and as a
divider. The common form of this tool has generally only one toe on the
caliper legs, but the double toes save the reversal of the points when
changing from outside to inside work. The divider points may be set at an
angle, which permits of stepping off readily around the outside of a shaft
at angular distances, where the ordinary dividers are useless. A number of
other uses could be mentioned, but any intelligent mechanic can readily
suggest them for himself.

[Illustration: Fig. 15. Combination Caliper and Divider]

Attachment for Vernier Calipers

While vernier and slide calipers are very handy shop tools, their
usefulness is much more limited than it ought to be for such expensive
instruments. In order to increase the usefulness of these tools, the
attachments shown in Fig. 16 may be made. In the upper left-hand part of
the engraving the details of a useful addition to the caliper are shown.
_A_ is made of machine steel, while the tongue _B_ is of tool steel,
hardened and ground and lapped to a thickness of 0.150 inch, the top and
bottom being absolutely parallel. This tongue is secured to _A_ by the two
rivets _CC_. The thumb-screw _D_ is used for fastening the attachment to
the sliding jaw of the vernier or slide caliper. In the upper part of the
engraving is shown the base, which is of machine steel, with the slot _F_
milled for the reception of the fixed jaw of the caliper. The set-screws
_GGG_ are put in at a slight angle so that the caliper will be held firmly
and squarely in this base. In the figure to the left these pieces are shown
in the position for forming a height gage, for which purpose the attachment
is most commonly used. As a test of the accuracy of its construction when
the attachment is placed in this position, the tongue _B_ should make a
perfect joint with the fixed jaw of the caliper, and the vernier should
give a reading of exactly 0.150. When it is desirable that the tongue _B_
should overhang, the base _E_ is pushed back even with the stationary jaw,
as shown in the engraving to the right. In this position it is used for
laying out and testing bushings in jigs, etc. The illustration shows the
tool in use for this purpose, _K_ being the jig to be tested. All
measurements are from the center line upon which the bushing No. 1 is
placed. Taking this as a starting point we find the caliper to read 1 inch.
Bushing No. 2, which is undergoing the test, should be 5/8 inch from this
center line. It has a 1/4-inch hole, and we therefore insert a plug of this
diameter. Now adjust the tongue of the caliper to the bottom of this plug
(as shown in the engraving) and the vernier should read 1.625 minus
one-half the diameter of the plug, or 1.500, and any variation from this
will show the error of the jig. In this case the top surface of _B_ was
used and no allowance had to be made for its thickness. In case the bottom
surface is used, 0.150 must be deducted from the reading of the caliper.

[Illustration: Fig. 16. Attachment for Vernier Calipers]

It is very easy to make a mistake in setting a bushing, and such a mistake
is equally hard to detect unless some such means of measuring as this is at
hand. It often happens that jigs and fixtures are put into use containing
such errors, and the trouble is not discovered until many dollars' worth of
work has been finished and found worthless. The illustration shows but one
of the many uses to which this attachment may be applied. The figures given
on the details are correct for making an attachment to be used upon the
Brown & Sharpe vernier caliper, but for other calipers they would, of
course, have to be altered to suit.[7]

Improved Micrometer Beam Caliper

[Illustration: Fig. 17. Improved Micrometer Beam Caliper]

In a beam caliper having a sliding micrometer jaw with or without a
separate clamping slide, it is necessary to have the beam divided into unit
spaces, at which the jaw or slide may be accurately fixed, the micrometer
screw then being used to cover the distance between the divisions; but it
is difficult to construct a beam caliper of this type with holes for a
taper setting pin, at exactly equal distances apart; consequently a plan
that is generally followed in making such tools is to provide as many holes
through the slide and beam as there are inch divisions, each hole being
drilled and reamed through both the slide and beam at once. If it were
attempted to drill the holes through the beam at exactly one inch apart,
having only one hole in the clamping head and using it as a jig for the
purpose, it would be found very difficult, if not impossible, to get the
holes all of one size and exactly one inch apart. The design of the
micrometer beam caliper shown in Fig. 17, which has been patented by Mr.
Frank Spalding, Providence, Rhode Island, is such, however, that it is not
necessary to drill more than one hole through the clamping slide. The beam
_F_ is grooved longitudinally, and in the groove are fitted hardened steel
adjusting blocks in which a taper hole _D_ is accurately finished. Between
the blocks are filling pieces _G_, which are brazed or otherwise fastened
in the groove. Holes are drilled, tapped, and countersunk between the
blocks and the filling pieces _G_, in which are fitted taper head screws
_EE_1_. The construction is thus obviously such that the blocks may be
shifted longitudinally by loosening one screw and tightening the other. In
constructing the caliper, the holes through the beam are drilled as
accurately as possible, one inch apart, and centered in the longitudinal
groove, but are made larger than the holes in the blocks, so as to provide
for slight adjustment.

Large Beam Caliper

[Illustration: Fig. 18. Large Beam Caliper]

Fig. 18 shows a large beam caliper designed for machinists and
patternmakers. It consists of a beam _MN_ and the legs _R_ and _S_, made of
cherry wood to the dimensions indicated. The legs are secured in position
on the beam by means of the thumb screws _A_, which jam against the gibs
_C_ at the points of the screws. The gibs have holes countersunk for the
screws to enter, to hold them approximately in place, and the nuts _B_ are
of brass, fitted into the filling pieces _P_ that keep them from turning.
The filling pieces are riveted to the legs by means of cherry dowels _D_.
One leg _S_ is provided with a fine adjustment consisting of flexible steel
spring _H_, ending in a point which is adjusted by the thumb screw _E_.
This screw is locked in adjustment by the check nut _G_ bearing against the
brass nut _F_, which is inserted in the leg as shown.[8]

       *       *       *       *       *


CHAPTER III

MICROMETER MEASURING INSTRUMENTS

Of all measuring instruments used in the shop intended for accurate
measurements, those working on the principle of the ordinary micrometer
calipers are the most common. In the present chapter we shall describe and
illustrate a number of different designs of these tools, intended to be
used for various purposes. The instruments shown in Figs. 19 to 23 were
built, in leisure hours, by Mr. A. L. Monrad, of East Hartford, Conn.

Micrometer for Snap Gages

[Illustration: Fig. 19. Micrometer for Snap Gages]

Fig. 19 shows a form of micrometer that has proved very handy for measuring
snap gages, and thicknesses, and can also be used as a small height gage to
measure the distance from a shoulder to the base, as shown in Fig. 20. In
measuring snap gages or thicknesses, the outside and inside of the
measuring disks are used, respectively. This instrument may also come in
very handy when setting tools on the planer or shaper. As will be seen in
the engraving, there are two sets of graduations on the sleeve _A_, thus
enabling the operator to tell at a glance what measurement is obtained from
the outside or the inside of the measuring disks. Each of the disks is
0.100 inch thick, so that the range of the micrometer is 0.800 and 1.000
inch for the outside and inside, respectively. The details of the
instrument are as follows:

The sleeve _A_ is composed of the inside measuring disk, the graduated
sleeve, and the micrometer nut combined. On the disk are two projections
_KK_, which are knurled, thus providing a grip when operating the tool. The
sleeve is threaded on the inside of one end, which acts as a micrometer
nut, and the outside of this same end is threaded to receive the adjusting
nut _D_. The sleeve has two slots, each placed 90 degrees from the
graduations, and these provide for compensation for wear. The disk part is
hardened by heating in a lead bath, and is finished by grinding and
lapping. The barrel _B_ is the same as a regular micrometer barrel, and is
graduated with 25 divisions. Spindle _E_ consists of the outside disk and
the micrometer screw, and the barrel _B_ fits on its end, which is tapped
out to receive the speeder _C_, which serves to hold the barrel in
position. The thread is 1/4 inch, 40 pitch, and the disk and unthreaded
parts are hardened, ground and lapped. To adjust this, instrument, loosen
the speeder _C_ and turn the barrel until the proper adjustment is
obtained. Then lock the barrel by tightening the speeder again.[9]

[Illustration: Fig. 20. Micrometer in Fig. 19 used as Height Gage]

Micrometer Caliper Square

Fig. 21 shows an assembled view and the details of a micrometer caliper
square which, if accurately made, is equal and often preferable to the
vernier caliper now so generally used. One of its advantages over the
vernier is that when the measurement is taken, it can be readily discerned
without straining the eyes, and this instrument is as easy to manipulate as
the regular micrometer.

In the details, part _A_, which is the main body of the instrument, is made
of tool steel, the forward or jaw end being solid with the body. This end
is hardened, and the jaw ground and lapped. The body is bored out and two
flats milled on the outside, which lighten it up and make it neat in
appearance. The jaw end is counterbored out with a 45-degree counterbore to
form a bearing for the forward end of the micrometer screw. A slot, 1/8
inch in width, extends from the fixed jaw to the other end, and in this
slides the movable jaw _C_. There are 44 divisions along the side of this
slot, each division being 0.050 inch apart, giving the tool a range of
2.000 inches for outside and 2.200 inches for inside measurements. The
screw _B_ is the most essential part of this tool, its construction
requiring great accuracy. Its diameter is 3/8 inch and it is cut with 20
threads per inch. On its forward end fits the cone _F_, which is hardened
and ground, the round part acting as the forward bearing of the screw and
fitting in the 45-degree counterbored hole in the body _A_. On its other
end fits the graduated barrel _D_ and also the speeder _G_.

[Illustration: Fig. 21. Micrometer Caliper Square]

The barrel is graduated in fifty divisions, each division equaling 0.001
inch. On the inside of the barrel is a 45-degree bearing which rides on the
cone _M_, the cone being held stationary on the end of the body. Thus it
will be seen that both front and back ends of the micrometer screw are
carried in cone bearings, which give a very small point of contact, thereby
causing but little friction and preventing any danger of gumming up so as
to run hard. The sliding jaw _C_ is made of tool steel, hardened, ground
and lapped, and combined with it is the micrometer nut which is drawn to a
spring temper. This nut is split and adjusted by two screws to compensate
for wear. On this jaw are the two zero marks that tell at a glance the
outside or inside measurements taken. The screw and washer, marked _H_ and
_I_, go onto the end of the micrometer screw and take up the end play. To
make a neat appearance, the cap _E_ is placed in the forward counterbored
hole, being held in place by a tight fit. The adjustment of the tool is
accomplished by loosening the speeder _G_ and turning the barrel on the
screw; when the adjustment is made, the speeder is again tightened down and
the barrel locked.[10]

Micrometer Depth Gage

The depth gage, shown in Fig. 22, has a 1/2-inch movement of the rod, and
may be used with rods of any desired length. These have small
45-degree-on-a-side grooves cut into them at intervals of 1/2 inch. A small
spiral spring, marked _I_, gives the rod a constant downward pressure, so
that, when taking a measurement, the base of the tool is placed on the
piece of work, and the rod always finds the bottom of the hole; then, by
tightening the knurled screw _F_ the rod is clamped in position and the
tool may be picked up and its measurement read from the dial. The
graduations on this instrument are similar to those of the vernier caliper,
only they are much plainer, as a half-inch movement of the rod turns the
dial one complete revolution. The figures on the dial denote tenths of an
inch, and those on the body of the tool thousandths; each graduation on the
dial is therefore equal to 0.010, so that to show the depth of a hole to be
0.373 the dial would be revolved around so that the seventh division beyond
the 3 mark would be near to 0, and then by looking from the 0 mark toward
the left, the third graduation on the body and one on the dial would be in
line, thus denoting 0.373.

[Illustration: Fig. 22. Micrometer Depth Gage]

The most essential part of this tool is the threaded screw _B_, which acts
as a rack, and the worm-wheel, solid with the dial _C_. The upper end of
the screw forms a split chuck which grips the measuring rods, while the
part marked _R_ is flatted off, and against this portion bears a threaded
sleeve _G_, which acts as a key to keep the screw in position. This sleeve
is threaded, both inside and outside, and screws into the body of the tool,
while the binding screw _F_ fits into it and binds against a small piece of
copper, marked _H_, which in turn holds the screw in position. The thread
on _B_ is 0.245 inch in diameter and is cut with 40 threads per inch. The
worm-wheel which meshes into this screw is solid with the dial, as shown at
_C_. It is 0.18 inch in diameter, and requires great accuracy in cutting;
it is not hobbed, but the teeth, of which there are twenty, are milled with
a circular cutter of the same diameter as the screw _B_ plus 0.002 inch.
The little studs, marked _EE_, on the dial and on the body _K_, hold the
coiled spring in position. Very great accuracy must be attained when
locating the holes in _K_ that are to receive the screw and dial _B_ and
_C_. The screw marked _J_ fits into the dial, where it serves as a bearing
and also holds the dial in position. The knurled cap _D_ tightens the split
chuck in order to hold the measuring rod firmly.[11]

Indicator for Accuracy of Lead-screws

[Illustration: Fig. 23. Indicator for Accuracy of Lead-screws]

All of the tools that have been described require an accurately cut screw,
and, as very few lathes are capable of producing this, it may be well to
illustrate an indicator for testing the accuracy of the lead-screw, and to
explain the method by which it is used. This instrument is shown in Fig.
23, where it is applied to a test screw _K_. It consists of a body _A_ on
one end of which is a projection _L_ serving as the upper bearing for the
pivoted lever _D_. This lever swings about a small steel pivot which can be
adjusted by the screw _E_. The rear end of the lever is forked, and between
the prongs is passed a thread making a double turn about the pivot _F_ that
carries the pointer _J_. Any movement of this lever will, therefore, cause
this pointer to revolve about the dial _C_. This dial has 20 divisions,
each indicating one-half thousandth of an inch movement of the front end of
the lever, so that a total revolution of the pointer about the dial would
indicate a movement of the front end of the lever of 0.020 inch. The screws
_I_ serve to hold the dial in place on the body of the indicator, while the
spring _M_ keeps the pointer normally at the zero mark. The indicator is
held in the toolpost by the arm _G_, which can be set at any angle and
firmly clamped by the screw _H_.

To use the indicator, remove the screw from a micrometer which is known to
be accurate, and, with the aid of a brass bushing, chuck it in the lathe so
that the thread end will project. Now gear the lathe to cut 40 threads per
inch and apply the indicator. When the lathe is started, the point of the
indicator follows along in the thread of the micrometer screw, and any
variation in the lead will be noted by a movement of the pointer over the
dial. If, on the other hand, no movement takes place, it is an indication
that the pitch of the lead-screw is correct.[12]

Micrometer Attachment for Reading Ten-thousandths of an Inch

[Illustration: Fig. 24. Micrometer with Attachment for Reading
Ten-thousandths of an Inch]

Fig. 24 shows an attachment for micrometers designed and made for readings
in tenths of thousandths of an inch. With very little fitting it is
interchangeable for 1-, 2-, or 3-inch B. & S. micrometers. The idea is
simple, as can be seen by the illustration. The diameter of the thimble is
increased 3 to 1 by a disk which is graduated with 250 lines instead of 25,
making each line represent 0.0001 inch instead of 0.001 inch. A piece of
steel is then turned up and bored and cut away so as to form the index
blade and a shell to clasp the micrometer frame, the whole thing being made
in one piece. The thimble disk being just a good wringing fit, it can be
easily adjusted 0 to 0. The attachment can be removed when fine measuring
is not required.[13]

Special Micrometer for Large Dimensions

Fig. 25 shows a 6-inch micrometer caliper designed for measuring from 0 to
6 inches by half-thousandths. The sliding micrometer head travels on a
cylinder barrel through which a hole is accurately bored to suit three
plugs, one, two, and three inches long, as shown in the engraving. These
plugs serve to locate the traveling head at fixed distances one inch apart.
The micrometer screw itself has a travel of one inch, like any standard
micrometer. A locknut is used to hold the screw in any desired position. A
thumb screw at the end of the barrel bears against the end plug, and zero
marks are provided to bring the screw against the plug with the same degree
of pressure at each setting. When the head is clamped by means of the
locking nut, it is as rigid as though it were solid with the barrel, and
the faces of the measuring points are thus always parallel.

[Illustration: Fig. 25. Special Micrometer for Large Dimensions]

Combination Micrometer

[Illustration: Fig. 26. Combined One- and Two-inch Micrometer]

A combined one- and two-inch micrometer is shown in Fig. 26. One side
records measurements up to one inch, and the other side up to two inches. A
single knurled sleeve or nut serves to move the double-ended measuring
piece one way or the other as desired, this piece having a travel of one
inch. The spindle is non-rotating, so that the faces of the screw and anvil
are always parallel. A locking device holds the screw in any position. This
tool is convenient for use both in measuring and as a gage, since it can be
conveniently held by the finger ring appearing at the back.

Micrometer Stop for the Lathe

Most micrometer lathe stops are limited in their use to work where only a
stationary height is required. It is, however, often necessary to use the
stop at different heights, to accommodate different lathes; then again, we
wish to use it on the right-hand side as well as the left. The form of
holder shown in Fig. 27 can be used either right or left, and for various
heights, and, by simply taking out the screw _A_, the micrometer may be
removed and used in any other form of holder desired.

[Illustration: Fig. 27. Micrometer Stop for the Lathe]

Both an assembled view and details of the holder are shown in the
engraving, so that it can be easily constructed by any one desiring to do
so. The micrometer and barrel may be procured from any of the manufacturers
of measuring instruments. The swivel _C_ is bored out so that the axis of
the micrometer screw will be parallel to the body of the holder when it is
in place. The swivel is made of tool steel and is fastened to the holder by
the screw _A_. It is hardened and lapped to a true bearing surface on the
sides and bottom, and so adjusted that it will turn to either side and
remain in the desired position without moving the screw. The holder _B_ is
milled through its entire length with a 90-degree cutter so that it will
fit along the ways of the lathe, and the bottom is lapped to a true
surface. For a neat appearance, the tool should be color hardened. On top
the holder is spotted or countersunk with a drill to form a recess for the
C-clamp. A knurled ring _D_ is driven onto the micrometer sleeve so that it
can be turned around to bring the graduations uppermost when the position
of the barrel is changed.[14]

Micrometer Surface and Height Gage

[Illustration: Fig. 28. Micrometer Surface and Height Gage]

Fig. 28 shows a form of surface gage that has proved very handy, and which
can be used also as a height gage for measuring distances from shoulders to
the base. If accurately made it is equal, and often preferable, to the
vernier or slide caliper now so generally used with an attachment to the
sliding jaw. One of its advantages over the vernier is the readiness with
which the graduations are discerned, and it is as easy to manipulate as the
ordinary micrometer. The part _B_, which forms the main body of the
instrument, is made of tool steel, and one end is fitted into the base
where it is held in position by the screw _D_. The remainder is milled to a
thickness of 1/8 inch and has graduations of 0.025 inch for a distance of
three inches. The screw _A_ is the most essential part of the tool, and its
construction requires great accuracy. Its diameter is 1/2 inch, and it is
cut with 20 threads per inch. In the upper end of the screw is driven the
ball _H_ for the sake of giving a neat appearance. The top of the thread is
turned off 0.010 inch to allow the scriber _F_ to slide freely on the
screw. The barrel _I_ is used for raising and lowering the slide, but
instead of having the graduations placed directly upon it, they are made
upon the sleeve _C_, which fits over a shoulder on the barrel. This allows
more easy means of adjustment than would be possible were the graduations
placed on the barrel itself. The sleeve is graduated with fifty divisions
each equaling a movement of the scriber of 0.001 inch. This sleeve may be
turned by means of a small spanner wrench so as to bring the zero line into
correct position to compensate for wear. A knurled locking nut is also
provided for holding the scriber in any fixed position. The scriber itself
is hardened and lapped to a finished surface, the tail end being slotted
and provided with two screws to compensate for wear. On the scriber is
placed the zero mark which shows at a glance the measurement that is being
taken. The block _K_ is three inches in height, and by using this block and
placing the gage on its top, the range of the gage is increased to six
inches. The screw _E_ is used for fastening the gage to the top of the
block. The center of the block is drilled out and slots cut through the
sides in order to make it light and neat in appearance.[15]

Micrometer of from One- to Five-inch Capacity

[Illustration: Fig. 29. Micrometer of from One- to Five-inch Capacity]

Fig. 29 shows a very simple and light five-inch micrometer that can be
quickly set to exact position from one to five inches. The round beam is
graduated by a series of angular grooves, 1 inch apart, which are of such a
form and depth that the clamping fingers at the end of part _A_ spring in,
allowing one inch adjustment of the beam to be quickly and positively made.
The sleeve _K_ is of tool steel, being counterbored from the forward end
for all but one-half inch of its length. For this half inch it is threaded
on the inside and acts as a micrometer nut. The outside of the same end is
threaded to receive the adjusting nut _F_, and two slots are cut in the
sleeve, at 90 degrees with the graduations. These slots, by a movement of
the nut _F_, provide a means for compensating for wear. The bushing _E_ is
hardened and lapped, and fitted tightly in the forward counterbore of this
sleeve, where it acts as a guide for the front end of the micrometer screw.
The barrel _J_ is the same as that of a regular micrometer, and is
graduated in 0.025 inch divisions.

The most essential part of the tool is the threaded screw _I_, over the end
of which fits the barrel _J_. The end is tapped out to receive the speeder
_H_, which serves to hold the barrel in position. The thread is 5/16 inch
in diameter, with 40 threads per inch, while the unthreaded part is
hardened, ground and lapped. To adjust the instrument, loosen the speeder
_H_ and turn the barrel until the proper adjustment is obtained; lock the
barrel by again tightening the speeder. The beam _C_ has a 1/4-inch hole
drilled throughout its entire length in order to make it light. Small
90-degree grooves are cut into it at intervals of 1 inch, and a 1/8-inch
slot is milled through one side to within 1-1/4 inch of the forward end.
The back end of part _A_ forms a spring-tempered split chuck, which grips
the beam and holds _A_ in position, while the exterior is threaded to
receive the knurled cap _B_ by which the chuck is tightened firmly to the
beam. From the front end, toward the split chuck, the body is counterbored
5/8 inch and the bushing _D_ driven in tight. This bushing has a key _G_
fitted into it, which slides in the slot of the beam and prevents the arm
from turning. The projecting arm is bored and tapped to receive the sleeve
_K_. This gage must be carefully and accurately made to be of value.[16]

Inside Micrometer for Setting Calipers

[Illustration: Fig. 30. Method of Setting Calipers from Inside Micrometers]

Fig. 30 shows an application of inside micrometers which is very handy. The
hole for the scriber in the scriber clamp of a surface gage is reamed out
to fit the rods used with inside micrometers. This forms a convenient
holder for the micrometer when used for setting outside calipers to it. The
calipers can be set easily and accurately at the same time, and where
extreme accuracy is not necessary this arrangement is more handy than that
of using large-sized micrometers.

With care and practice an accuracy of within one-quarter of 0.001 inch is
obtainable in this way. Mistakes, in fact, are more easily guarded against
than is the case when using the micrometers directly.

Micrometer Frame

[Illustration: Fig. 31. Useful and Handy Micrometer Frame]

Fig. 31 shows a micrometer frame used some years ago at the Westinghouse
works. The frame is an aluminum casting, and the anvil is simply a
tool-steel pin, which fits well in the hole into which it is inserted, and
can be clamped anywhere within the limits of its length. The micrometer end
of the frame is supplied with an inside micrometer head. The tool is
adjusted to a gage, either to a standard pin gage, or to an inside
micrometer gage. The capacities of three of these micrometers in a set may
be from about 3-1/2 to 7 inches, 6 to 11 inches, and 10 to 15 inches. When
the head is turned outward, as shown in the lower view in the cut, the tool
is very handy around a horizontal boring machine where a pin gage cannot be
used without removing the boring bar.

Micrometer Stop for the Lathe

[Illustration: Fig. 32. Micrometer Stop for the Lathe]

The simple micrometer stop shown in Fig. 32 is used on the engine lathe for
obtaining accurate movements of the lathe carriage. It consists of a
micrometer head, which can be purchased from any micrometer manufacturer,
and a machine steel body which is bored to fit the micrometer head. This
tool is clamped on the front way of the lathe bed, and when the jaw of the
micrometer is against the lathe carriage, it can easily be adjusted to a
thousandth of an inch. Of course, care should be taken not to bump the
carriage against the micrometer.[17]

Use of Micrometer for Internal Thread Cutting

[Illustration: Fig. 33. Method of using Micrometer for Internal Thread
Cutting]

Fig. 33 illustrates a means of determining the size of internally threaded
work. The work shown is intended for a lathe chuck. The outside diameter of
the hub on the work is turned to the same size as the hubs on small
faceplates which are furnished with all new lathes. The threaded size is
then taken and transferred with a micrometer, over the anvil of which is
fitted a 60-degree point as shown enlarged at _A_. In connection with a
graduated cross-feed screw this greatly facilitates the work over the usual
cut-and-try method.[18]

Inside Micrometer

The inside micrometer shown in sections in Figs. 34 and 35 is adapted to
measuring, by use of extension rods, from 2 inches up to any size of hole,
and has one inch adjustment of the measuring screw.

[Illustration: 35]

Referring to the section shown in Fig. 35, the measuring screw _S_ is
secured to the thimble _B_ with the screw _D_, the head of which is
hardened and forms the anvil. By loosening this screw _D_, the thimble can
be rotated to compensate for wear. The wear of the measuring screw and nut
is taken up by screwing the bushing _A_ into the frame with the wrench
shown in Fig. 37. This bushing is split in three sections for about
two-thirds of its length on the threaded end. The three small lugs on the
wrench fit into these slots. The handle end of the wrench is a screw driver
which is used for manipulating the set screw _C_. The bushing is made an
easy fit in the frame on its plain end and tapered, as shown, on its
outside threaded part. This thread being the same pitch as the measuring
screw, adjustment for wear does not affect the reading of the micrometer.
This manner of adjustment brings the nut squarely down on the measuring
screw for its whole length, presenting the same amount of wearing surface
after adjustment as when new.

[Illustration: Fig. 36. Handle for Inside Micrometer]

[Illustration: Fig. 37. Wrench used with Inside Micrometer]

The point _F_, which is hardened on its outer end, screws into the frame,
and is secured by the taper-headed screw _O_, which screws into and expands
the split and threaded end of the point _F_. The handle, Fig. 36, clamps
over the knurled part of the frame for use in small, deep holes. The rods,
six in number, running from 1 to 6 inches inclusive, are made by screwing a
sleeve onto a rod with a hardened point and locking it with a taper-headed
screw on its threaded and split end, the same as in the point _F_. The
extension pieces, Fig. 38, are adjustable, on their socketed ends, in the
same way, and run in lengths of 6, 12, 18 inches, etc.[19]

[Illustration: Fig. 38. Adjustable Extension Pieces for Inside Micrometer]

Direct Fractional-reading Micrometer

[Illustration: Fig. 39. Direct Fractional-reading Micrometer]

The direct fractional-reading micrometer shown in Fig. 39 is the result of
talks with many mechanics in which all agreed that such a feature added to
a micrometer would, by making it both a fractional and decimal gage, more
than double its practical value. While approximate readings in 64ths, etc.,
may be obtained by the graduations on the barrel _B_ as on an ordinary inch
scale, the exact readings of 64th, etc., may be obtained only by reference
to graduations on the movable thimble _A_. There are but eight places on
_A_ which coincide with the long graduation line on _B_ when any 64th, 32d,
16th, or 8th is being measured, and each of these eight places is marked
with a line, and the 64th, 32d, 16th, or 8th for which that line should be
used is marked thereon. (See _a_ and _b_, Fig. 40.) The line _a_ would be
used for 3/32, 7/32, 11/32, etc., and the line _b_ for 1/64, 9/64, 17/64,
etc. Now suppose we wish to accurately measure 15/32 inch. We first roughly
read it off the inch scale on sleeve _B_ by turning out thimble _A_. Having
secured it closely by drawing edge of _A_ over that graduation, we find
that the line _a_ (Fig. 40) on the movable thimble very nearly or exactly
coincides with the long graduation line on _B_. When these lines coincide,
we have the exact measurement of 15/32 inch without reference to how many
thousandths may be contained in the fraction. Thus all through the scale
any fraction may be found instantly. There is no mental arithmetic, use of
tables, or memory work in using the tool. The new graduations are
independent of the old, and may be used equally well with or without them.

[Illustration: Fig. 40. Graduations on the Fractional-reading Micrometer]

Micrometers may also be graduated as in Fig. 41. Instead of using the zero
line on _A_ as a base line, a point is taken one-fifth of a turn around
_A_, and the graduated scale on _B_ is placed to correspond, as shown in
the engraving; also, instead of making lines _a_, _b_, etc., on _A_, full
length, they are made about half an inch long, and the numerators are
entirely omitted and the denominators placed at the end instead of under
the line. To the ordinary user of the tool, this is all that is necessary
for a perfectly clear reading of the fractions.[20]

[Illustration: Fig. 41. Another Method of Graduating for Fractional
Reading]

Sensitive Attachment for Measuring Instruments

No matter how finely and accurately micrometers and verniers may be made,
dependence must in all cases be placed on the sensitiveness of a man's hand
to obtain the exact dimensions of the piece to be measured. In order to
overcome this difficulty and eliminate the personal equation in the
manufacture of duplicate and interchangeable parts, the sensitive
attachment to the micrometer shown in Fig. 42 may be used, and will be
found of much value.

[Illustration: Fig. 42. Sensitive Micrometer Attachment]

The auxiliary barrel _A_ is held to the anvil of the micrometer by means of
a thumb screw _B_. At the inside end of the barrel is a secondary anvil
_C_, the base of which bears against the short arm of the indicating lever
_D_. The action will be clearly seen by reference to the engraving. The
micrometer is so set that when a gage, _G_, of exact size, is placed
between the measuring points, the long arm of the indicator stands at the 0
mark. If the pieces being calipered vary in the least from the standard
size it will be readily noted by the movement of the pointer. Hard rubber
shapes turned from rough casting often vary from 0.003 to 0.005 inch after
having passed the inspector's test with an ordinary micrometer. With this
attachment the inspector's helper can detect very minute variations from
the limit size. Anything within the limits of the micrometer can be made to
show to the naked eye variations as small as a ten-thousandth inch.[21]

Another Sensitive Micrometer Attachment

[Illustration: Fig. 43. Another Sensitive Micrometer Attachment]

When testing the diameters of pieces that are handled in great quantities
and are all supposed to be within certain close limits of a standard
dimension, the ordinary micrometer presents the difficulty of having to be
moved for each piece, and small variations in diameters have to be
carefully read off from the graduations on the barrel. Not only does this
take a comparatively long time, but it also easily happens that the
differences from the standard diameter are not carefully noted, and pieces
are liable to pass inspection that would not pass if a convenient
arrangement for reading off the differences were at hand. Fig. 43 shows a
regular Brown & Sharpe micrometer fitted with a sensitive arrangement for
testing and inspecting the diameters of pieces which must be within certain
close limits of variation. The addition to the ordinary micrometer is all
at the anvil end of the instrument. The anvil itself is loose and consists
of a plunger _B_, held in place by a small pin _A_. The pin has freedom to
move in a slot in the micrometer body, as shown in the enlarged view in the
cut. A spring _C_ holds the plunger _B_ up against the work to be measured,
and a screw _D_ is provided for obtaining the proper tension in the spring.
The screw and the spring are contained in an extension _E_ screwed and
doweled to the body of the micrometer. A pointer or indicator is provided
which is pivoted at _F_ and has one extensional arm resting against the pin
_A_, which is pointed in order to secure a line contact. At the end of the
indicator a small scale is graduated with the zero mark in the center, and
as the indicator swings to one side or the other the variations in the size
of the piece measured are easily determined. A small spring _G_ is provided
for holding the pointer up against the pin _A_. The case _H_ simply serves
the purpose of protecting the spring mentioned. As the plunger _B_ takes up
more space than the regular anvil, the readings of the micrometer cannot be
direct. The plunger _B_ can be made of such dimensions, however, that 0.100
inch deducted from the barrel and thimble reading will give the actual
dimension. Such a deduction is easily done in all cases. In other words,
the reading of the micrometer should be 0.100 when the face of the
measuring screw is in contact with the face of the plunger; the 0.100 inch
mark is thus the zero line of this measuring tool.

When desiring to measure a number of pieces, a standard size piece or gage
is placed between the plunger _B_ and the face _L_ of the micrometer screw,
and the instrument is adjusted until the indicator points exactly to zero
on the small scale provided on the body of the micrometer. After this the
micrometer is locked, and the pieces to be measured are pushed one after
another between the face _L_ and the plunger _B_, the indications of the
pointer _M_ being meanwhile observed. Whenever the pointer shows too great
a difference, the piece, of course, does not pass inspection. All
deviations are easily detected, and any person of ordinary common sense can
be employed for inspecting the work.

Micrometer Scale

[Illustration: Fig. 44. Micrometer Mounted on Machinist's Scale]

A micrometer, mounted as shown in Fig. 44 is very handy. The micrometer may
be used in combination with a 4-, 6-, 9-, or 12-inch scale. It can be
adjusted on standard plugs, or one can make a set of gages up to 12 inches,
out of 3/16-inch round tool steel wire, and use these for setting. In
mounting the micrometer, before cutting it apart, mill the shoulders shown
at _A_, and in milling the bottom pieces _B_, use a piece of machine steel
long enough for both, cutting the piece in half after milling the slots. In
this way one obtains perfect alignment. In a shop where a set of large
micrometers is not kept, this arrangement is very useful.[22]

       *       *       *       *       *


CHAPTER IV

MISCELLANEOUS MEASURING TOOLS AND GAGES

Among the miscellaneous measuring tools and gages dealt with in this
chapter are tools and gages for measuring and comparing tapers, adjustable
gages, radius gages, gages for grinding drills, sensitive gages, tools for
gaging taper threaded holes, contour gages, etc. Of course, these are
offered merely as examples of what can be done in the line of measuring
tools for different purposes, and, while having a distinct and direct value
to the mechanic, they also have a great indirect value, because they
furnish suggestions for the designing and making of tools for similar
purposes.

Tool for Measuring Tapers

[Illustration: Fig. 45. Taper Measuring Tool]

Fig. 45 shows a tool which has proved very useful. It is a tool for
measuring tapers on dowel pins, reamers, drill shanks, or anything to be
tapered. Most machinists know that to find the taper of a shank they must
use their calipers for one end and reset them for the other end; or else
caliper two places, say, three inches apart, and if, for instance, the
difference should be 1/16 inch, they must multiply this difference by four
to get the taper per foot. With the tool above mentioned, all this trouble
in calipering and figuring is saved. Simply place the shank or reamer to be
measured between pins _A_, _B_, _C_, and _D_, and slide _H_ and _K_
together. Then the taper can be read at once on the graduated scale at _L_.
The construction of the tool will be readily understood. The body or base
_F_ has a cross piece supporting the two pins _A_ and _B_. On this slides
piece _K_, which has at its right end the graduated segment. The screw _G_
is fast to piece _K_, and upon it swivels the pointer _E_, which carries
the two pins _C_ and _D_. Thus these two pins can be brought into contact
with a tapered piece of any diameter within the capacity of the tool, and
the swivel screw _G_ allows the pins to adjust themselves to the taper of
the work and the pointer _E_ to move to the left or right, showing
instantly the taper per foot.

As the pins _A_ and _B_ are 1-1/2 inch apart, which is 1/8 of a foot, and
the distance from _G_ to _L_ is 4-1/2 inches, which is three times longer
than the distance between _A_ and _B_, the graduations should be 3/64 inch
apart, in order to indicate the taper per foot in eighths of an inch.[23]

Taper Gage

[Illustration: Fig. 46. Handy Taper Gage]

A handy taper gage is shown in Fig. 46. The blades of the gage are made of
tool steel. The edge of the blade _A_ is V-shaped, and the blade _B_ has a
V-groove to correspond. The end of _B_ is offset so as to make the joint
and allow the two blades to be in the same plane. A strong screw and nut
are provided to hold the blades at any setting. The user of this gage looks
under the edge of _A_, and is thereby enabled to tell whether the taper
coincides with that set by the gage, and also where a taper piece needs
touching up to make it true.[24]

Test Gage for Maintaining Standard Tapers

[Illustration: Fig. 47. Test Gage for Maintaining Standard Tapers]

In steam injector work, accurately ground reamers of unusual tapers are
commonly required, and the gage shown in Fig. 47 was designed to maintain
the prevailing standard. It consists of a graduated bar, 1 inch square,
with the slot _F_ running its entire length. The stationary head _A_ is
secured in position flush with the end of the bar, and the sliding head _B_
is fitted with a tongue which guides it in the slot. This head may be
secured in any desired position by means of a knurled thumb nut. The
bushings _D_ and _D'_ are made of tool steel, hardened and ground to a
knife edge on the inside flush with the face. All bushings are made
interchangeable as to outside diameter.

The head _B_ is fitted with an indicating edge _E_ which is set flush with
the knife edge of the bushing. The reading indicates to 0.010 inch the
distance the bushings are from each other, and the difference in their
diameter being known, it is easy to compute the taper. With this gage it is
possible to maintain the standard tapers perfectly correct, each reamer
being marked with the reading as shown by the scale.[25]

Inside and Outside Adjustable Gages

[Illustration: Fig. 48. Adjustable Gage for Inside and Outside
Measurements]

Fig. 48 shows an inside and an outside adjustable gage for accurate work,
used in laying out drill jigs, and in setting tools on lathes, shapers,
planers, and milling machines. The outside gage is shown in the side view
and in the sectional end view marked _Y_. At _X_ in the same figure is a
sectional end view showing how the gage is constructed for inside work. The
top and bottom edges are rounded, so that the diameters of holes may be
easily measured.

The gage consists of a stepped block _B_, mounted so as to slide upon the
inclined edge of the block _C_. There are V-ways upon the upper edge of the
latter, and the block _B_ is split and arranged to clamp over the ways by
the screw shown at _S_. All parts of the gage are hardened and the faces of
the steps marked _A_, are ground and finished so that at any position of
the slide they are parallel to the base of the block _C_. The lower split
portion of the block is spring-tempered to prevent breaking under the
action of the screw, and also to cause it to spring open when loosened. The
gage has the advantage that it can be quickly adjusted to any size within
its limits, which does away with using blocks. In planing a piece to a
given thickness, the gage may be set to that height with great accuracy by
means of a micrometer caliper, and then the planer or shaper tool adjusted
down to the gage. This method does away with the "cut-and-try" process, and
will bring the finishing cut within 0.001 inch of the required size. If the
piece being planed, or the opening to be measured, is larger than the
extreme limit of the gage, parallels may be used. In fitting bushings into
bushing holes, the adjustable gage may be moved out to fit the hole, and
then, when the bushing is finished to the diameter given by the gage, as
determined by a micrometer caliper, a driving fit is ensured.[26]

Radius Gage

[Illustration: Fig. 49. Radius Gage]

Fig. 49 shows a radius gage which has proved to be very handy for all such
work as rounding corners or grinding tools to a given radius. The blades
are of thin steel, and are fastened together at the end by a rivet, thus
forming a tool similar to the familiar screw pitch gage. The right-hand
corner of each blade is rounded off to the given radius, while the
left-hand corner is cut away to the same radius, thus providing an
instrument to be used for either convex or concave surfaces. The radius to
which each blade is shaped is plainly stamped upon the side.[27]

Gage for Grinding Drills

[Illustration: Fig. 50. Gage for Grinding Drills]

Fig. 50 shows a gage for use in grinding drills, which has been found very
handy and accurate. This gage enables either a large or small drill to lie
solidly in the groove provided for it on top of the gage, and the lips can
then be tested for their truth in width, or angle, much easier and quicker
than with the gages in common use without the groove. There is a line, to
set the blade _B_ by, on the stock at an angle of 59 degrees at the top of
the graduated blade, and the user can easily make other lines, if needed
for special work. The blade is clamped in position by the knurled nut _N_
at the back, and can be thus adjusted to any angle. The stock _A_ is cut
away where the blade is pivoted on, so that one side of the blade comes
directly in line with the middle of the groove.[28]

Tool for Gaging Taper Threaded Holes

[Illustration: Fig. 51. Tool for Gaging Taper Threaded Holes]

The tool shown in Fig. 51 is used for gaging taper threaded holes in
boilers when fitting studs. It is a simple, though very useful and
economical tool, and it will doubtless be appreciated by those having much
work of this kind to do. The hole in which the stud is to be fitted is
calipered by filling the threads of the plug with chalk, and then screwing
the plug in the hole. When the plug is removed the chalk will show exactly
the largest diameter of the hole.[29]

Contour Gage

[Illustration: Fig. 52. Setting Contour Gage to Turned Sample]

[Illustration: Fig. 53. End View of Contour Gage]

Figs. 52, 53 and 54 illustrate a special tool which will be found of great
value in certain classes of work. The need of some such device becomes
apparent when patterns and core boxes are required to be accurately checked
with the drawings of brass specialties, in particular. The tool is applied
to the work, and the wires pressed down onto the contour by using the side
of a lead pencil. Of course, patterns parted on the center could have their
halves laid directly on the drawing without using the contour gage, but
some patterns are cored and inseparable. Such a tool proves a relentless
check upon the patternmaker, who, by making the patterns larger than
necessary, can cause a considerable loss in a business where thousands of
casts are made yearly from the same patterns. As a ready and universal
templet it is very useful.[30]

[Illustration: Fig. 54. Testing Core-box with Gage]

Testing a Lead-screw

[Illustration: Fig. 55. Micrometer for Testing Lathe Lead-screw]

A reliable way for testing the pitch of a lead-screw, at any position of
its length, is to procure a micrometer screw and barrel complete, such as
can be purchased from any of the manufacturers of accurate measuring
instruments, and bore out a holder so that the axis of the micrometer screw
will be parallel to the holder when the screw is in place, as shown in Fig.
55. With the lathe geared for any selected pitch, the nut engaged with the
lead-screw, and all backlash of screw, gears, etc., properly taken up,
clamp the micrometer holder to the lathe bed, as shown in Fig. 56, so that
the body of the holder is parallel to the carriage. Adjust the micrometer
to one inch when the point of the screw bears against the carriage and with
a surface gage scribe a line on the outer edge of the faceplate. Now rotate
the lathe spindle any number of full revolutions that are required to cause
the carriage to travel over the portion of the lead-screw that is being
tested, bringing the line on the faceplate to the surface gage point. If
the distance traveled by the carriage is not greater than one inch, the
micrometer will indicate the error directly. For lengths of carriage travel
greater than one inch, an end measuring rod, set to the number of even
inches required, can be used between the micrometer point and lathe
carriage. The error in the lead-screw is then easily determined by the
adjustment that may be required to make a contact for the measuring points
between the carriage and the micrometer screw. The pitch can be tested at
as many points as are considered necessary by using end measuring rods, of
lengths selected, set to good vernier calipers. The style of holder shown
can, with the micrometer screw, be used for numerous other shop tests, and
as the screw is only held by friction caused by the clamping screw, it can
easily be removed and placed in any form of holder that is found
necessary.[31]

[Illustration: Fig. 56. Testing a Lathe Lead-screw]

Simple Tool for Measuring Angles

[Illustration: Fig. 57. Special Tool for Measuring Angles]

Fig. 57 shows a very simple, but at the same time, a very ingenious tool
for measuring angles. Strictly speaking, the tool is not intended for
measuring angles, but rather for comparing angles of the same size. The
illustration shows so plainly both the construction and the application of
the tool, that an explanation would seem superfluous. It will be noticed
that any angle conceivable can be obtained in an instant, and the tool can
be clamped at this angle by means of screws passing through the joints
between the straight and curved parts of which the tool consists. Linear
measurements can also be taken conveniently, one of the straight arms of
the tool being graduated. As both of the arms which constitute the actual
angle comparator are in the same plane, it is all the easier to make
accurate comparisons. This tool is of German design, and is manufactured by
Carl Mahr, Esslingen a. N.

Bevel Gear-testing Gage

[Illustration: Fig. 58. Sensitive Gear-testing Gage]

In Fig. 58 is shown a sensitive gage for inspecting small bevel gears. The
special case shown to which the gage is applied in the engraving is a small
brass miter gear finished on a screw machine, in which case some of the
holes through the gears were not concentric with the beveled face of the
gears, causing the gears to bind when running together in pairs. The gage
shown is quite inexpensive, but it indicates the slightest inaccuracy.

       *       *       *       *       *


NOTES

[1] MACHINERY, October, 1897.

[2] M. H. Ball, April, 1902.

[3] M. H. Ball, February, 1901.

[4] Harry Ash, April, 1900.

[5] M. H. Ball, March, 1903.

[6] Ezra F. Landis, May, 1902.

[7] L. S. Brown, March, 1903.

[8] C. W. Putnam, October, 1901.

[9] Jos. M. Stabel, May, 1903.

[10] Jos. M. Stabel, May, 1903.

[11] Jos. M. Stabel, May, 1903.

[12] Jos. M. Stabel, May, 1903.

[13] P. L. L. Yorgensen, February, 1908.

[14] A. L. Monrad, December, 1903.

[15] A. L. Monrad, December, 1903.

[16] A. L. Monrad, December, 1903.

[17] J. L. Marshall, February, 1908.

[18] Charles Sherman, November, 1905.

[19] M. H. Ball, May, 1903.

[20] Chas. A. Kelley, May, 1908.

[21] H. J. Bachmann, December, 1902.

[22] Wm. Ainscough, May, 1908.

[23] John Aspenleiter, October, 1900.

[24] W. W. Cowles, June, 1901.

[25] I. B. Niemand, December, 1904.

[26] Geo. M. Woodbury, February, 1902.

[27] A. Putnam, July, 1903.

[28] M. H. Ball, October, 1901.

[29] F. Rattek, January, 1908.

[30] Howard D. Yoder, December, 1907.

[31] W. Cantelo, July, 1903.






End of the Project Gutenberg EBook of Measuring Tools, by Unknown

*** 