# Crankshafts Ø3, Ø5 and Ø8 with full-length D-flat

> What crankshaft sizes fit the 623, 625 and 608 bearings on a model Stirling engine?

- Category: Stirling engines › Drives & mechanisms
- Kind: Hardware
- Basis: Solid shafts at the 623 / 625 / 608 bore Ø; Ø5 and Ø8 with a 0.5 mm D-flat along the whole length
- Page: https://xemstudio.com/objects/stirling-crankshafts/ · JSON: https://xemstudio.com/api/geometry?object=stirling-crankshafts · Plain text: https://xemstudio.com/objects/stirling-crankshafts/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

**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.

## Notes

- Solid round shafts with 0.3 chamfers on both ends. Ø3 × 40, 44, 60 and 80 are plain round; Ø5 × 80, 100, 120, 150 and Ø8 × 80, 100, 120 have a D-flat 0.5 deep along the whole length (4.5 and 7.5 across the flat).
- The flat is where the M3 grubs in crank discs, webs and flywheel hubs bear, so the hubs cannot turn on the shaft. It also gives the shaft a flat face to lie on.
- Ø3: the crank head's 623 towers and the Ø3-bore crank discs. Ø5: the 625 crank stands, rhombic gears, crank discs and Ø5 flywheel hubs. Ø8: the tri-clamp crank frame's 608s, crank webs and Ø8 flywheel hubs.
- Lengths on the engines here: 2 in gamma Ø5 × 100 between two 625 stands with the flywheel outside; tri-clamp crank frame Ø8 × 80; rhombic gear shafts Ø5 × 80, one × 120 to carry the flywheel; can engine Ø3 × 44 and LTD Ø3 × 40 (a crank disc at each end, bearings and flywheel between).

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| shafts, rods, pins | Ø3 / Ø5 / Ø8 | the bores listed on each mating object | slide | all |
| D-flat | 0.5 deep | M3 grubs in hubs | designed | crankshaft-* |

## Sizes

| file | Ø | length | D-flat | fits |
|---|---|---|---|---|
| crankshaft-3x40 | 3 | 40 | — | 623; crank-disc-b3 |
| crankshaft-3x44 | 3 | 44 | — | 623; crank-disc-b3 |
| crankshaft-3x60 | 3 | 60 | — | 623; crank-disc-b3 |
| crankshaft-3x80 | 3 | 80 | — | 623; crank-disc-b3 |
| crankshaft-5x80-dflat | 5 | 80 | 0.5 full length (4.5) | 625; crank discs; Ø5 hubs |
| crankshaft-5x100-dflat | 5 | 100 | 0.5 full length (4.5) | 625; crank discs; Ø5 hubs |
| crankshaft-5x120-dflat | 5 | 120 | 0.5 full length (4.5) | 625; crank discs; Ø5 hubs |
| crankshaft-5x150-dflat | 5 | 150 | 0.5 full length (4.5) | 625; crank discs; Ø5 hubs |
| crankshaft-8x80-dflat | 8 | 80 | 0.5 full length (7.5) | 608; crank webs; Ø8 hubs |
| crankshaft-8x100-dflat | 8 | 100 | 0.5 full length (7.5) | 608; crank webs; Ø8 hubs |
| crankshaft-8x120-dflat | 8 | 120 | 0.5 full length (7.5) | 608; crank webs; Ø8 hubs |

## Where the files are

- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (11 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/stirling-crankshafts/index.json

- crankshaft-3x40: [STEP](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-3x40.step) · [STL](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-3x40.stl) — Ø3 × 40 solid crankshaft for the crank head's 623 towers and the Ø3-bore crank discs; can engine skewer replacement
- crankshaft-3x44: [STEP](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-3x44.step) · [STL](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-3x44.stl) — Ø3 × 44 solid crankshaft for the crank head's 623 towers and the Ø3-bore crank discs; can engine skewer replacement
- crankshaft-3x60: [STEP](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-3x60.step) · [STL](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-3x60.stl) — Ø3 × 60 solid crankshaft for the crank head's 623 towers and the Ø3-bore crank discs; can engine skewer replacement
- crankshaft-3x80: [STEP](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-3x80.step) · [STL](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-3x80.stl) — Ø3 × 80 solid crankshaft for the crank head's 623 towers and the Ø3-bore crank discs; can engine skewer replacement
- crankshaft-5x80-dflat: [STEP](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-5x80-dflat.step) · [STL](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-5x80-dflat.stl) — Ø5 × 80 crankshaft with a full-length 0.5 mm D-flat (4.5 across) for the grubs; 625 crank stands, rhombic gears, crank discs, nut flywheel b5.
- crankshaft-5x100-dflat: [STEP](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-5x100-dflat.step) · [STL](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-5x100-dflat.stl) — Ø5 × 100 crankshaft with a full-length 0.5 mm D-flat (4.5 across) for the grubs; 625 crank stands, rhombic gears, crank discs, nut flywheel b5.
- crankshaft-5x120-dflat: [STEP](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-5x120-dflat.step) · [STL](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-5x120-dflat.stl) — Ø5 × 120 crankshaft with a full-length 0.5 mm D-flat (4.5 across) for the grubs; 625 crank stands, rhombic gears, crank discs, nut flywheel b5.
- crankshaft-5x150-dflat: [STEP](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-5x150-dflat.step) · [STL](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-5x150-dflat.stl) — Ø5 × 150 crankshaft with a full-length 0.5 mm D-flat (4.5 across) for the grubs; 625 crank stands, rhombic gears, crank discs, nut flywheel b5.
- crankshaft-8x80-dflat: [STEP](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-8x80-dflat.step) · [STL](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-8x80-dflat.stl) — Ø8 × 80 crankshaft with a full-length 0.5 mm D-flat (7.5 across); tri-clamp crank frame 608s, crank webs, flywheels b8.
- crankshaft-8x100-dflat: [STEP](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-8x100-dflat.step) · [STL](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-8x100-dflat.stl) — Ø8 × 100 crankshaft with a full-length 0.5 mm D-flat (7.5 across); tri-clamp crank frame 608s, crank webs, flywheels b8.
- crankshaft-8x120-dflat: [STEP](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-8x120-dflat.step) · [STL](https://xemstudio.com/files/hardware/stirling-shafts-and-rods/crankshaft-8x120-dflat.stl) — Ø8 × 120 crankshaft with a full-length 0.5 mm D-flat (7.5 across); tri-clamp crank frame 608s, crank webs, flywheels b8.

## How it fits

### Parts that fit it
- [Scotch yoke: slotted yoke and crank disc, 20 and 30 mm stroke](https://xemstudio.com/objects/scotch-yoke/): crank disc on a Ø5 shaft
- [Geneva drive: 4 and 6 station wheels, R30, with drive discs](https://xemstudio.com/objects/geneva-drive/): Ø5 shafts for wheel and drive
- [Spoked flywheels Ø50 to Ø150 × 10](https://xemstudio.com/objects/spoked-flywheels/): Ø5 / Ø8 bore, M3 grub on the flat
- [Counterweighted crank discs, Ø5 bore, 10 to 30 mm stroke](https://xemstudio.com/objects/counterweighted-crank-discs/): Ø5 bore, M3 grub on the flat
- [Crank webs (bar cranks), Ø5 bore, 10 to 30 mm stroke](https://xemstudio.com/objects/crank-webs-5mm-bore/): Ø5 bore, M3 grub
- [Shaft adapter Ø5 to Ø8 × 20](https://xemstudio.com/objects/shaft-adapter-5-to-8mm/): Ø5 bore on the D-flat shaft
- [Crank discs Ø30 for a Ø3 crankshaft, 10 to 20 mm stroke](https://xemstudio.com/objects/crank-discs-3mm-bore/): Ø3 crankshaft in the bore

### Goes in or on
- [Crank stands with a 625 pocket, 40 and 60 mm axis height](https://xemstudio.com/objects/crank-stands-625/): Ø5 shaft in the stands' 625s
- [Tri-clamp power piston: ring-less full-bore pistons Ø34.8, Ø47.5 and Ø72.9](https://xemstudio.com/objects/tri-clamp-power-piston/): Ø8 shaft in the crank frame's 608s

### Connects to
- [Crank discs for a Ø5 shaft, 10 to 30 mm stroke](https://xemstudio.com/objects/crank-discs-5mm-bore/): Ø5 bore, M3 grub on the flat
- [Flywheels Ø100–Ø200 with hex-nut rim pockets](https://xemstudio.com/objects/nut-pocket-flywheels/): Ø3 / Ø5 / Ø8 hub, M3 grub on the flat

### Also needed
- [Shaft spacers for Ø3, Ø5 and Ø8 shafts, 1 to 5 mm](https://xemstudio.com/objects/shaft-spacers/): set the 1 mm gaps along the shaft
- [Ball bearings, 683 to 6210 and flanged F6xx (ISO 15)](https://xemstudio.com/objects/ball-bearings-metric/): 623 / 625 / 608

## Questions

**What diameter crankshaft does a model Stirling engine need?**

The bore of its bearings: Ø3 in 623s, Ø5 in 625s, Ø8 in 608s. The Ø5 and Ø8 files carry a 0.5 mm D-flat along their whole length.

**Why a D-flat?**

So the M3 grub in each crank disc, web and flywheel hub bears on a flat and the hub cannot slip round the shaft.

**How is this different from the metric shafts page?**

Those have a 20 mm motor-style flat 0.1 × d deep at one end; these have a 0.5 mm flat along the whole length so a hub can sit anywhere.

## Fits with

- [Metric shafts Ø3 to Ø10 with D-flats and clip grooves](https://xemstudio.com/objects/metric-shafts/)
- [Crank discs for a Ø5 shaft, 10 to 30 mm stroke](https://xemstudio.com/objects/crank-discs-5mm-bore/)
- [Crank stands with a 625 pocket, 40 and 60 mm axis height](https://xemstudio.com/objects/crank-stands-625/)
- [Flywheels Ø100–Ø200 with hex-nut rim pockets](https://xemstudio.com/objects/nut-pocket-flywheels/)
- [Shaft spacers for Ø3, Ø5 and Ø8 shafts, 1 to 5 mm](https://xemstudio.com/objects/shaft-spacers/)
- [Ball bearings, 683 to 6210 and flanged F6xx (ISO 15)](https://xemstudio.com/objects/ball-bearings-metric/)