V0.04 Probe Z Axis Construction
All the printed parts for the probe and probe holder are found on one 3D print sheet (maus_probe.stl). The probe consists of two rails and adjustable slider together with a locking thumbscrew allowing the probe's initial height to be adjusted. These parts are attached to the perforated plate on an Axis Driver. The sliding arm holds a Probe Tip that can be rotated on its axis, allowing the tip to be positioned in two dimensions. Moving the slide under the probe adds another two dimensions, making it possible to manually position the tip anywhere in the printer's working volume. Two identical Probe Arms are supplied, one for making a coarse tip, and one for a fine tip.
You will need to construct one Axis Driver for use with the Probe Z Axis.
Electrochemically etched point (left) compared to a 0.5mm diameter hypodermic needle point
The Probe Tip requires a fine, conductive point. Suitable ready-made points for coarse tips include 0.5mm or finer hypodermic needles, and 40mm+ acupuncture needles. Be careful with it, 007. If using a hypodermic needle, carefully crush the plastic connector on it with pliers or a vise and rotate the needle to remove it from the crushed remains. Remove all the fragments from the needle shaft (scraping with the back of a scalpel blade works well). Fine hypodermic needles are generally shorter than the Probe Arm. If so, take an approximately 60mm length of bare solid wire that will fit within the blunt end of the needle, and very delicately crimp it there with wire cutters.
Coarse tips are recommended while familiarity is developed with the μRepRap system. For the time being, instructions on how to fabricate a fine, electrochemically etched point can be found on Printables here.
Probe Rail captive nut slot
Both Probe Rails have a cavity for an M3 nut. Only one is needed, but inserting both will allow the Thumbscrew to be mounted on either side, giving greater flexibility in workspace layout and the handedness of the operator.
Fitting the Probe Rails and Probe Holder to the Z Axis Driver
Loosely attach the two Probe Rails to the outermost holes on the front of the perforated plate on the Axis Driver with four M3 x 15mm screws. The nut cavities should face the plate, and the two slight recesses on the rails should face each other.
Note: The holes in this plate are smaller than an M3 screw and do not need nuts. This is because in development it ran out of room between the flexures. Retrospectively, this was a poor choice and may change.
Fit the Probe Holder between the Probe Rails with its bracket towards the motor end of the Axis Driver. Use this as a guide, and squeeze the Probe Rails against it. Firmly fasten the rails to the plate while allowing just enough room for the Probe Holder to slide between them.
Thumbscrew
Insert an M3 x 20mm screw into the cavity on the Thumbwheel. Secure it firmly in place with an M3 nut. Insert the shaft into one of the holes in the side of a Probe Rail and gently screw into place. This is used to lock the Probe Holder in position, and very little force is required to do this.
Crimped hypodermic needle in Probe Arm groove
Take the needle or wire you will use as a tip and lay it in the groove on the Probe Arm with 10mm of its tip overhanging. Lay a fine bead of cyanoacrylate adhesive along the groove and allow it to cure.
Insert an M3 x 15mm screw into the hole in the Probe Arm from the smooth side. Wrap the wire from the hypodermic (or acupuncture needle etc.) once around the M3 screw shaft clockwise as viewed from the screw tip. Put an M3 nut on the screw and wind it down until it holds the wire in place. Tighten the screw, driving the nut into the captive nut cavity in the Probe Arm and firmly trapping the wire in place. Trim excess wire. This provides a conductive path from the probe tip to the protruding screw.
Probe Arm fitted with a tip made from a hypodermic needle
Holding the Probe Arm at its tip with pliers, use needle-nosed pliers or a haemostat to bend the protruding point down away from the groove by about 60 degrees. The objective is to bend the point down so that it can probe a surface, but not bend it so much that the view of it is obscured by the rest of the tip.
To reduce vibration of the probe tip, cover the bend generously with hot melt adhesive above and below. Remove excess adhesive filaments with a flame.
Electrochemically etched tips will need careful storage, and plans for a suitable box are available on GitHub.
Probe Arm/Probe Tip and short Dupont cable connected to Probe Holder
Twist one end of the Z Touch probe wire from the CNC controller into a loop that will fit an M3 screw. Put the screw on the Probe Arm into the hole in the Probe Holder. Slip the loop of wire over the protruding end of the screw followed by a washer and secure with an M3 nut.
It is often useful to be able to disconnect the Z Touch probe wire to manually measure resistance on the tip, and the oft-used Dupont jumper wire is generally not very robust. Also, it is convenient to completely remove the Probe Holder from the Probe Rails when changing the Probe Arm. So it makes sense to make a short cable out of heavier wire with the loop on one end and a Dupont plug on the other, which can be readily connected and disconnected.
A 5.5mm nut driver is handy for fastening or undoing this nut, but do not over-tighten or it will be difficult to make fine manual adjustments to the angle of the Probe Arm.
The Probe Z Axis Assembly is now complete.
Ensure the Probe Holder is firmly clamped by the Probe Rails. Check conductivity between the Z Touch probe wire and the Probe Tip. You may choose to remove the Probe Arm or the Probe Holder at this point to avoid stabbing yourself during later assembly.
The Probe Z Axis Assembly is now ready to be integrated with the support structure.