# Print-in-place: ratchet with flexible pawls (12 teeth, one-way)

> How do you 3D print a working ratchet (one-way clutch) in one piece?

- Category: 3D printing › Print-in-place mechanisms
- Kind: Hardware
- Basis: Xem Studio design: internal ratchet teeth, compliant pawl arms, 45° V-groove bearing; one designed running gap of 0.40 mm
- Page: https://xemstudio.com/objects/print-in-place-ratchet-flexible-pawl/ · JSON: https://xemstudio.com/api/geometry?object=print-in-place-ratchet-flexible-pawl · Plain text: https://xemstudio.com/objects/print-in-place-ratchet-flexible-pawl/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files Xem Studio Design License (free to use and sell from, not to redistribute as files: https://xemstudio.com/license/)
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

## Overall (mm)

| length | width | height |
|---|---|---|
| 76.0 | 76.0 | 28.0 |

**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- 3D print in place — prints already assembled, moving, in one job. Drawn at true size with no printer tolerance added; the 0.40 mm running gaps are part of the design.
- Running gap 0.40 mm per side, 0.80 mm on diameter — part of the design, drawn as is. On the 45° faces the same 0.40 mm is measured square to the face (0.57 mm along the axis).
- Bed: flat. The frame ring and the wheel both stand on the bed; in the bottom 6 mm layer the frame carries 12 internal ratchet teeth and the wheel two thin arms whose tips sit in tooth spaces, 0.40 mm clear.
- Support while printing: above the teeth the frame closes inward as a 45° cone over the arms (0.40 mm square to the arm tips' top corners) and then wraps the wheel's raised boss with a 45° V-ridge in a V-groove; the boss and knob are plain cylinders. Nothing overhangs more than 45°.
- Captured: the V-ridge in the boss's V-groove holds the wheel up and down; the boss runs in the ridge with 0.40 mm all round.
- Freeing it: hold the frame and turn the knob in the free direction one full turn (12 clicks); flex each arm once with a fingertip through the top if it feels stuck.
- Motion: free direction — continuous, the arm tips ride up the 3 mm ramps (bending 3.1 mm inward) and drop off each locking face: 12 clicks per turn. Locking direction — it turns 0.77° until a pawl tip meets a tooth face, then stops (computed).

## Sizes

| key | value | what |
|---|---|---|
| gap_mm | 0.4 | running gap per side on every moving interface (radial, axial, under captured parts) — part of the design, not a tolerance |
| frame_od_mm | 76.0 |  |
| teeth | 12 | internal ratchet teeth (radial locking face, straight ramp) |
| tooth_depth_mm | 3.0 | root Ø60, tip Ø54 |
| pawls | 2 | flexible arms on the wheel, 180° apart (both engage) |
| pawl_arm_mm | 1.6 wide × 100° of arc | on Ø51.5 |
| pawl_flex_mm | 3.06 | arm-tip travel inward to pass a tooth |
| lock_play_deg | 0.77 | free turn in the locking direction before a pawl meets a tooth face |
| clicks_per_turn | 12 | free direction |
| knob_d_mm | 43.48 | wheel boss / knob |
| axial_play_mm | 0.57 |  |
| height_mm | 28.03 | as printed |
| mount_holes | 3 × Ø3.4 | frame |

## Where the files are

- Xem Studio: [Print-in-place mechanism design (geometry computed in the generator)](https://xemstudio.com/) — web — Xem Studio design

## Free STEP/STL (3 parts, Xem Studio Design License, Xem Studio)

Index: https://xemstudio.com/files/hardware/print-in-place-ratchet-flexible-pawl/index.json · license: https://xemstudio.com/files/hardware/print-in-place-ratchet-flexible-pawl/LICENSE.md

- print-in-place-ratchet-flexible-pawl-assembly: [STEP](https://xemstudio.com/files/hardware/print-in-place-ratchet-flexible-pawl/print-in-place-ratchet-flexible-pawl-assembly.step) · [STL](https://xemstudio.com/files/hardware/print-in-place-ratchet-flexible-pawl/print-in-place-ratchet-flexible-pawl-assembly.stl) — The whole print as laid on the bed (2 bodies, already assembled); STEP keeps each moving body a separate solid
- print-in-place-ratchet-flexible-pawl-frame: [STEP](https://xemstudio.com/files/hardware/print-in-place-ratchet-flexible-pawl/print-in-place-ratchet-flexible-pawl-frame.step) · [STL](https://xemstudio.com/files/hardware/print-in-place-ratchet-flexible-pawl/print-in-place-ratchet-flexible-pawl-frame.stl) — Frame ring Ø76 with 12 internal teeth, 45° cone and V-ridge bearing, 3 × Ø3.4
- print-in-place-ratchet-flexible-pawl-wheel: [STEP](https://xemstudio.com/files/hardware/print-in-place-ratchet-flexible-pawl/print-in-place-ratchet-flexible-pawl-wheel.step) · [STL](https://xemstudio.com/files/hardware/print-in-place-ratchet-flexible-pawl/print-in-place-ratchet-flexible-pawl-wheel.stl) — Wheel with two flexible pawl arms, boss with 45° V-groove, knob with pointer slot

## Questions

**Which part flexes?**

The two pawls are thin arms (1.6 mm wide, 100° of arc) cut into the wheel; a 3.2 mm slot behind each lets it bend inward over the teeth.

**How much backlash does it have?**

0.77° in the locking direction — the 0.40 mm gap between pawl tip and tooth face, seen from the axis.

## Fits with

- [Print-in-place: captive wheel on a printed axle (Ø40 × 12)](https://xemstudio.com/objects/print-in-place-captive-wheel-axle/)
- [Print-in-place: barrel hinge, three knuckles, folds 180° (48.8 mm)](https://xemstudio.com/objects/print-in-place-barrel-hinge-180/)
- [Print-in-place: seven-knuckle hinge on a captive through-pin (58.4 mm)](https://xemstudio.com/objects/print-in-place-multi-knuckle-hinge/)
- [Print-in-place: captive turntable with V-ridge retention (Ø80 platter)](https://xemstudio.com/objects/print-in-place-captive-turntable/)
- [Print-in-place: linear slider on a dovetail rail with end stops (100 mm)](https://xemstudio.com/objects/print-in-place-dovetail-slider/)
- [Print-in-place: articulated chain, 6 links, 20 mm pitch](https://xemstudio.com/objects/print-in-place-articulated-chain/)
- [Print-in-place: captive ball joint, Ø24 ball, limited cone](https://xemstudio.com/objects/print-in-place-ball-joint/)