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Scotch yoke: slotted yoke and crank disc, 20 and 30 mm stroke
How do I make a Scotch yoke with 3D printed parts? · Hardware · basis: Textbook Scotch yoke: slider displacement = r·sin θ, stroke = 2r; slot sized to a 623 bearing (OD 10) on a Ø3 crank pin, Ø5 shaft
Long Earth Society build part. Displacer drive without a wrist pin, used on the LES rigs. The engines
Exact dimensions. Every file is drawn at true size with no printing tolerance. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your printer's or process's clearance before making the part. Mating features
- sizes
- 2 in table
Notes
- A crank pin rides in a slot across the yoke, so the yoke moves as a pure sine of crank angle with no connecting rod and no rod angularity.
- Stroke is twice the pin offset: the 20 mm crank has its pin hole at 10 mm, the 30 mm crank at 15 mm.
- The slot is 10 mm wide for a 623 bearing (OD 10) on a Ø3 pin through the crank disc; the rod end has a Ø3 hole for the next link.
- Shorter than a crank and con-rod for the same stroke; used to drive displacers and pumps.
Sizes
| stroke | parts | slot | crank pin offset |
|---|---|---|---|
| 20 mm | yoke + crank disc | 10 × 30 mm | 10 mm |
| 30 mm | yoke + crank disc | 10 × 40 mm | 15 mm |
Mating features
Drawn at the exact size. Open press, slide, run and socket features by your process's clearance; leave designed gaps and clamp fits as drawn.
| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| yoke slot width | 10 | 623 bearing OD 10 (rolls in it) | run | scotch-yoke-* |
| crank bore | Ø5 | Ø5 shaft | press | scotch-yoke-* |
| crank pin hole | Ø3 | Ø3 pin | press | scotch-yoke-* |
| rod-end hole | Ø3 | Ø3 pin (turns in it) | run | scotch-yoke-* |
Where the files are
Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.
| Wikipedia | Scotch yoke | web | CC BY-SA 4.0 (text) |
| Long Earth Society | Engine and rig builds on extrusion frames | web, video | LES site |
Free files
★ Free files 4 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json
| scotch-yoke-20-yoke | Scotch yoke slider, 20 mm stroke, 10 mm slot for a 623 bearing on the crank pin, 8 mm rod with a Ø3 end hole | STEP · STL |
| scotch-yoke-20-crank | Scotch yoke crank disc, Ø3 pin hole at 10 mm (20 stroke), Ø5 bore | STEP · STL |
| scotch-yoke-30-yoke | Scotch yoke slider, 30 mm stroke, 10 mm slot | STEP · STL |
| scotch-yoke-30-crank | Scotch yoke crank disc, Ø3 pin hole at 15 mm (30 stroke), Ø5 bore | STEP · STL |
Plain text: sheet.txt · JSON: /api/geometry?object=scotch-yoke
How it fits
Goes in or on
Stirling shafts and rodscrank disc on a Ø5 shaftConnects to
Four-bar linksØ3 hole in the rod endAlternatives
Swash platemulti-cylinder from one shaft
Eccentric and straprotary to linear, no slot
Crank discs, connecting rods and flywheels for…crank and con-rodAlso needed
Ball bearings, 683 to 6210 and flanged F6xx623 on the crank pin, in the slot
Dowel pins, 2–6 mmØ3 crank pinQuestions
What is a Scotch yoke and when is it better than a con-rod?
A pin in a slot: the slider moves as a pure sine of crank angle with no connecting rod, so it is shorter and has no rod angularity. The pin takes the side load, so it carries a 623 bearing in the slot.
How do I get the stroke I want?
Stroke = 2 × the crank pin offset. Pick the 20 or 30 mm crank disc, or move the pin hole to half the stroke you need.