A collet holder for a standard Crayola crayon. Turn the nut and six fingers close on the crayon. This page shows the three versions that have been built so far: v1 and v3 were printed, v4 is the latest and has not been printed yet.
| v1 | v3 | v4 | |
|---|---|---|---|
| Status | Printed. Tines snapped after repeated unscrewing | Printed. Thread engages only about 2 mm at first touch | Not printed yet |
| Widest point | 32 mm (side tab) | 20 mm | 19 mm |
| Nut diameter | 24 mm | 20 mm | 18.5 mm |
| Length, nut tight | 29.8 mm | 33.2 mm | 35.8 mm |
| Thread | Ø17 × 3 mm | Ø14.4 × 2.5 mm | Ø14.4 × 2.5 mm |
| Thread length | 13.5 mm | 4.5 mm | 8.5 mm |
| Thread engaged at first touch | 10.4 mm | 2.0 mm | 6.0 mm |
| Slot roots | inside the thread, 0.45 mm round end | above the thread, 1.1 mm keyhole | above the thread, 1.1 mm keyhole |
| Bore under the nut | full length | relieved, grip lands under the cone | relieved, grip lands under the cone |
| Nut cone relief | none | none | 0.25 mm |
| Plastic volume | 10.6 cm³ | 7.2 cm³ | 6.5 cm³ |
Six fingers end in a 10° cone. The nut has the same cone, with 0.25 mm of extra clearance. Turning it clockwise (looking at the crayon tip) pulls the cone down over the fingers.
The bore is 0.25 mm wider except right under the cone, so the crayon is pinched where the nut pushes. That keeps the load out of the finger roots, where v1 broke.
The cord pulls the holder one way while a child pulls the crayon the other. The floor only stops pushing in, so grip comes from friction. A ridged collet is included for more.
Tapered tail on the bed, crayon opening up. Layers run across the fingers, so use PETG, ASA or nylon. PLA tends to crack at the finger roots.
Nose on the bed, threaded end up. The inner cone and 40° thread flanks print without supports. The wall is about 1 mm thick at the grip flutes, so use 3 or more perimeters.
| Setting | Value |
|---|---|
| Layer height | 0.2 mm |
| Walls / top / bottom | 4 walls (1.6 mm) · 4 top · 4 bottom layers |
| Infill | 40 % (the fingers and threads are all wall) |
| Temperature / fan | about 10 °C above normal for the collet, fan low, for layer bonding |
| Supports / brim | none / none (both ends taper in, so they sit flat) |
| Outer walls | slow, about 30 mm/s, for clean threads |
| Slicer check | collet and nut have no layer overhanging more than 50° |
| Crayon (Crayola regular) | 92.2 × 7.9 mm |
| Relaxed bore | Ø8.3 mm |
| Bore depth | 26.0 mm (66.2 mm of crayon sticks out) |
| Fingers | 6, 0.9 mm slots, 16 mm long |
| Cone | 10° half angle, 6 mm long |
| Thread | Ø14.4 × 2.5 mm, right hand, 8.5 mm long |
| Collet body | Ø19 × 33 mm |
| Nut | Ø18.5 × 27.3 mm, 12 shallow flutes |
| Nut travel | 0.79 turn from first touch to hard stop |
| Cord hole | Ø3.4 teardrop, across the rear |
| Push-out hole | Ø2.4 mm through the floor |
| Symptom | Change |
|---|---|
| Crayon is hard to insert | BORE_D +0.1 |
| Crayon rattles when loose | BORE_D −0.1 |
| Nut binds on the thread | THREAD_CLR +0.05 |
| Nut wobbles on the thread | THREAD_CLR −0.05 |
| Not enough grip | print the ridged collet |
| Nut wall feels thin | R_OUT_N 9.5 |
These names are constants at the top of crayon_leash_v4.py. Re-run it to get new STLs.
Tighten by hand only. Stop when the crayon no longer slides. Forcing the nut against the hard stop loads the finger roots.
Cord. Thread it through the rear hole and tie a knot larger than the hole. To use a snap hook, loop a short piece of cord through the hole and clip onto the loop. A version with a small side tab for clipping directly is also included. Keep the leash off the child's neck and limbs.
Small parts. The nut comes off the crayon end when unscrewed. Keep that in mind for children under three.
Checked, not yet printed. The v4 meshes are watertight, the threads clear each other at every nut position, and the layer-by-layer overhang check passed. Treat the bore and thread clearances as a starting point.