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Piccolo Fabrication Guide
We suggest using a combination of MDF or hardboard together with acrylic for making Piccolos. We settled on this combination as we found MDF on acrylic produced the least friction between moving parts. Hardboard works similarly well, but the cut edges can be a bit more charred and require a light sand. If using hardboard, use dry processed board that is smooth on both sides.
A 100% wood Piccolo also works, as does a 100% acrylic one, however acrylic tends to create more friction and is more brittle, so the parts will be more suspect to breakages. The cutting pattern is tailored to the tolerances below, so if making your piccolo entirely from acrylic, you may want to adjust the cutting pattern.
The current Piccolo v1 cutting pattern is designed for 3mm material. Recommended thickness are:
- MDF parts: between 2.75 and 3.10mm
- Acrylic parts: between 2.90 and 3.20mm
- The gears: equal to or thinner than the other acrylic parts, but greater than 2mm.
(note, 1/8 inch material may work, but the slots will be a bit tight and may need adjusting. See Adjusting the Cutting Pattern.)
Whilst thicknesses in this range will work, it is important that the material thickness is consistent across the panel. MDF and Hardboard is generally pretty consistent, whilst Acrylic can vary in thickness across a single sheet. Extruded acrylic is recommended over cast acrylic as it will have a more consistent thickness, however it is more expensive.
Why different tolerances for the MDF vs the acrylic parts? On average we have found the acrylic sheets to be slightly thicker, so we've allowed for this in the design.
###PCB Substitute Part###
If not using a Piccolo pcb, you should use the pcb outline to cut a substitute part to use in its place as this holds piccolo together. The pcb outline is included in the cutting pattern.
Use 1.5 or 2mm acrylic or similar for this. Thicker material can be used if you use longer screws.
###Paper Spacers### In order to get a good fit for its moving parts, Piccolo uses paper spacers to adjust its tolerances. The paper spacers are generally needed if the acrylic is thicker or the same thickness as the MDF, if the Acrylic is thinner then the spacers may not be needed. Multiple layers can be used - the cutting pattern includes two sets of spacers. We have found that thin card, around 160gsm, provides a good amount of flexibility in adjusting the fit without being too finicky to work with. Thinner paper will also work fine, but more layers will be needed.
###Colours### We've used coloured gears and paper spacers to add flavour to our Piccolos. One thing to note about using coloured and clear acrylic together is that your coloured material could be slightly thicker - this is bad and will cause your gears to catch! Make sure the gear material is thinner than, or the same thickness as, the surrounding parts.
We don't recommend painting or dying your MDF or hardboard parts, as this will also affect your tolerances and can create friction. Rubbing a wood stain into your material can work however, and it is also possible to find coloured fibreboards (difficult however, to find in 3mm or 1/8in?). We have a made a few Piccolos out of black MDF from Ventech in Australia.
Laser cutting leaves a kerf (gap in the material) when it cuts. The cutting pattern accounts for a kerf of about 0.2mm, however the exact kerf will vary between machines. If you are doing your own cutting and would like to adjust for the kerf, see Adjusting the Cutting Pattern. Laser cutting will also leave a draft angle on cut edges, and this is compensated for in the design by flipping any mating parts. That said, if the draft is too extreme, this will start to affect the tolerances in other areas.
A professional cutting service will likely give you a good quality cut with minimal kerf and draft, that should give you some decent working Piccolos. Dirty lenses or a lower quality machine will leave you with a wider kerf, greater draft and rougher edges, and your Piccolo is more likely to have a few issues.
For a prettier Piccolo, we suggest putting a protective paper coating on your MDF or Hardboard to remove scorch and flashback. If you are using a cutting service, just ask them if they offer this as well. You can also sand these marks off rather than use a paper backing, but this may affect your tolerances.
###Tabs and Labels###
All parts in the cutting pattern are tabbed into panels for each material, and the breaks in the lines are replaced with lines for etching, to help with breaking out the parts. If using a cutting service, make sure you tell your fabricator about the tabs, to avoid confusion. We recommend a 50% depth etch for the tabs and labels.
##Adjusting the Cutting Pattern##
If you would like to make changes to the cutting pattern, we suggest you download the untabbed version:
This has all the complete shapes with compound shapes released, making it much easier to edit.
A list of edits you might consider, the offsets we have used, and other things to keep in mind (all dim's in mm. These are the dimensions in the drawing and account for kerf. "Offset" means offset from the nominal material thickness dimension of 3mm):
- If changing material thickness, you will need to change the slot dimensions:
- Y-rail slot in Y7 - current offset -0.05 - this mates with X3 "the tooth", and if too tight will restrict the Y-axis, if too loose will not hold the Y-gear flush on the rack and will create backlash. It's hard to get this part just right every time, we suggest cutting it slightly tight and then sanding down X3 to get the perfect fit.
- Y-chassis wall slots in Y5 & Y1 - current offset -0.035 - a tight fit in these slots keeps the Z-stage perpendicular.
- Tooth slots in X1 & X4 - current offset -0.07 - these hold onto the tooth and the Y-rail, and should be snug. Any wiggle with be translated to the output motion.
- Slots in penholder parts - current offset +0.10 - these should be loose enough to assemble without breaking the parts.
- Slots in faceplate for toolhead - current offset +0.20 - loose to allow for easy attachment/detatchment of the toolhead.
- All other slots have no offset.
- If using different sized fasteners you may need to adjust the screw holes:
- Holes in all parts - current dia 2.9 - we found this to be a good size for a snug fit but still be easy to insert the screws.
- Holes in Y1 & Z2 - current dia 2.75 - these are slightly smaller to allow for threading onto the screws, and can substitute for nuts, which can be useful if the material is too thick and there end up being not enough threads on the screws to fit the nuts.
- In order to use a different servo model, you will probably need to make a few adjustments:
- Keyhole shapes for Servos in X1, X4 and Y - these hold the servos in place and should be tight. If you adjust this, make sure you keep the axis of the servo shaft in the same point. This is the center of the large circle of the keyhole shape.
- Servo mount slots in X5A & X5B - these do not need to be tight, but their vertical position keeps the servo shaft in the right position relative to the rack.
- Servo spline(teeth in the gear that mates with the servo) - this will be impossible to draw without trial and error. Via testing a bunch of servos we've collected a lot of spline shapes, take a look at these in the servo tester folder to see if we've got one you are looking for: tba.
- If you are having issues with wider-than-average kerf, one of the key parts to edit would be the racks and gears. First try giving an offset to the racks, then try increasing the offset on the gears, until you get a well meshing fit. Current offsets are:
- Racks - no offset
- Gears - +0.20 offset