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Nut-weighted flywheels: Ø100–200 with hex pockets for M8, M10, M12, 3/8 and 1/2 in nuts
How do I make a 3D-printed flywheel heavy enough for a Stirling engine? · Hardware · basis: Hex nut envelopes from ISO 4032 (M8 13 × 6.8, M10 16 × 8.4, M12 18 × 10.8) and ASME B18.2.2 finished hex (3/8 in 9/16 × 21/64, 1/2 in 3/4 × 7/16 in); pockets drawn at the nut's nominal across-corners (press fit; nut masses computed from the hex envelope in steel, weigh yours
Long Earth Society build part. Flywheels you load with hardware-store nuts. The engines
- sizes
- 8 in table
Notes
- A printed flywheel is too light to carry a Stirling through its cycle; Each wheel has a ring of hex pockets with one flat facing outward, so every nut sits the same way, flush with the face, and the rim holds it against centrifugal load.
- Pockets come in multiples of six, so you can fill all of them (maximum inertia, balanced), every other one (half the weight, still balanced), every third, or only one half (a counterweight: the half opposite the crank pin). Press the nuts in; a drop of CA or a strip of tape over the face holds them for good.
- Hub: Ø3 (Ø100 and Ø120 only: can engine, LTD and crank-head Ø3 shafts), Ø5 (625 crank stands, rhombic gears, the gamma and alpha crankshafts) or Ø8 (tri-clamp crank frame), with an M3 grub on the shaft's D-flat; no adapter needed.
- Sizing: a 2 in tri-clamp gamma on a tea light runs well on Ø150 with a full set of M10 nuts (18 nuts, ~190 g, about +7.6 kg·cm² at the rim); the can engine on Ø100 M8 half-filled; LTDs want the lightest wheel that keeps them turning (start half-filled and add). Print flat, 4 walls, 30 % infill; the nuts are the mass.
- LES: the flywheels on the engines.
- Fits are designed in: every hole is the mating part's size plus the clearance for the joint (press 0, slide +0.2, running pin +0.3, bearing / magnet / nut pocket +0.2, large sleeve +0.3 mm on diameter), so the parts print and go together as they are, in any material. Tapped holes are 2.5 mm for M3.
Sizes
| od_mm | nut | pockets | pocket_radius_mm | rim_mm | nut_g_each | full_set_g | added_inertia_kg_cm2 | bores |
|---|---|---|---|---|---|---|---|---|
| 100 | M8 | 12 | 40.5 | 8.3 | 5.6 | 67 | 1.1 | 3 / 5 / 8 |
| 120 | M10 | 12 | 49.0 | 9.9 | 10.3 | 124 | 3.0 | 3 / 5 / 8 |
| 120 | 3/8 in | 12 | 49.9 | 9.8 | 7.8 | 93 | 2.3 | 3 / 5 / 8 |
| 150 | M10 | 18 | 64.0 | 9.9 | 10.3 | 186 | 7.6 | 5 / 8 |
| 150 | M12 | 12 | 63.0 | 12.3 | 16.0 | 192 | 7.6 | 5 / 8 |
| 150 | 1/2 in | 12 | 62.5 | 12.6 | 18.5 | 221 | 8.6 | 5 / 8 |
| 200 | M12 | 18 | 88.0 | 12.3 | 16.0 | 288 | 22.3 | 5 / 8 |
| 200 | 1/2 in | 18 | 87.5 | 12.6 | 18.5 | 332 | 25.4 | 5 / 8 |
Where the files are
Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.
| ISO | ISO 4032 Hexagon regular nuts (style 1) | standard | ISO verify |
| ASME | ASME B18.2.2 Nuts for general applications | standard | ASME verify |
| Long Earth Society | Engine builds | web, video | LES site |
Free files
★ Free files 24 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json
| flywheel-100-m8-b3 | Ø100 flywheel, 12 pockets for M8 hex nuts at R40.5 (one flat facing out), Ø3 hub with M3 grub, 8.3 thick rim; full set ≈ 67 g of nuts, +1.1 kg·cm² | STEP · STL |
| flywheel-100-m8-b5 | Ø100 flywheel, 12 pockets for M8 hex nuts at R40.5 (one flat facing out), Ø5 hub with M3 grub, 8.3 thick rim; full set ≈ 67 g of nuts, +1.1 kg·cm² | STEP · STL |
| flywheel-100-m8-b8 | Ø100 flywheel, 12 pockets for M8 hex nuts at R40.5 (one flat facing out), Ø8 hub with M3 grub, 8.3 thick rim; full set ≈ 67 g of nuts, +1.1 kg·cm² | STEP · STL |
| flywheel-120-m10-b3 | Ø120 flywheel, 12 pockets for M10 hex nuts at R49.0 (one flat facing out), Ø3 hub with M3 grub, 9.9 thick rim; full set ≈ 124 g of nuts, +3.0 kg·cm² | STEP · STL |
| flywheel-120-m10-b5 | Ø120 flywheel, 12 pockets for M10 hex nuts at R49.0 (one flat facing out), Ø5 hub with M3 grub, 9.9 thick rim; full set ≈ 124 g of nuts, +3.0 kg·cm² | STEP · STL |
| flywheel-120-m10-b8 | Ø120 flywheel, 12 pockets for M10 hex nuts at R49.0 (one flat facing out), Ø8 hub with M3 grub, 9.9 thick rim; full set ≈ 124 g of nuts, +3.0 kg·cm² | STEP · STL |
| flywheel-120-3-8in-b3 | Ø120 flywheel, 12 pockets for 3/8 in hex nuts at R49.9 (one flat facing out), Ø3 hub with M3 grub, 9.8 thick rim; full set ≈ 93 g of nuts, +2.3 kg·cm² | STEP · STL |
| flywheel-120-3-8in-b5 | Ø120 flywheel, 12 pockets for 3/8 in hex nuts at R49.9 (one flat facing out), Ø5 hub with M3 grub, 9.8 thick rim; full set ≈ 93 g of nuts, +2.3 kg·cm² | STEP · STL |
| flywheel-120-3-8in-b8 | Ø120 flywheel, 12 pockets for 3/8 in hex nuts at R49.9 (one flat facing out), Ø8 hub with M3 grub, 9.8 thick rim; full set ≈ 93 g of nuts, +2.3 kg·cm² | STEP · STL |
| flywheel-150-m10-b5 | Ø150 flywheel, 18 pockets for M10 hex nuts at R64.0 (one flat facing out), Ø5 hub with M3 grub, 9.9 thick rim; full set ≈ 186 g of nuts, +7.6 kg·cm² | STEP · STL |
| flywheel-150-m10-b8 | Ø150 flywheel, 18 pockets for M10 hex nuts at R64.0 (one flat facing out), Ø8 hub with M3 grub, 9.9 thick rim; full set ≈ 186 g of nuts, +7.6 kg·cm² | STEP · STL |
| flywheel-150-m12-b5 | Ø150 flywheel, 12 pockets for M12 hex nuts at R63.0 (one flat facing out), Ø5 hub with M3 grub, 12.3 thick rim; full set ≈ 192 g of nuts, +7.6 kg·cm² | STEP · STL |
| flywheel-150-m12-b8 | Ø150 flywheel, 12 pockets for M12 hex nuts at R63.0 (one flat facing out), Ø8 hub with M3 grub, 12.3 thick rim; full set ≈ 192 g of nuts, +7.6 kg·cm² | STEP · STL |
| flywheel-150-1-2in-b5 | Ø150 flywheel, 12 pockets for 1/2 in hex nuts at R62.5 (one flat facing out), Ø5 hub with M3 grub, 12.6 thick rim; full set ≈ 221 g of nuts, +8.6 kg·cm² | STEP · STL |
| flywheel-150-1-2in-b8 | Ø150 flywheel, 12 pockets for 1/2 in hex nuts at R62.5 (one flat facing out), Ø8 hub with M3 grub, 12.6 thick rim; full set ≈ 221 g of nuts, +8.6 kg·cm² | STEP · STL |
| flywheel-200-m12-b5 | Ø200 flywheel, 18 pockets for M12 hex nuts at R88.0 (one flat facing out), Ø5 hub with M3 grub, 12.3 thick rim; full set ≈ 288 g of nuts, +22.3 kg·cm² | STEP · STL |
| flywheel-200-m12-b8 | Ø200 flywheel, 18 pockets for M12 hex nuts at R88.0 (one flat facing out), Ø8 hub with M3 grub, 12.3 thick rim; full set ≈ 288 g of nuts, +22.3 kg·cm² | STEP · STL |
| flywheel-200-1-2in-b5 | Ø200 flywheel, 18 pockets for 1/2 in hex nuts at R87.5 (one flat facing out), Ø5 hub with M3 grub, 12.6 thick rim; full set ≈ 332 g of nuts, +25.4 kg·cm² | STEP · STL |
| flywheel-200-1-2in-b8 | Ø200 flywheel, 18 pockets for 1/2 in hex nuts at R87.5 (one flat facing out), Ø8 hub with M3 grub, 12.6 thick rim; full set ≈ 332 g of nuts, +25.4 kg·cm² | STEP · STL |
| nut-m8 | M8 hex nut, 13 across flats × 6.8: the flywheel weight | STEP · STL |
| nut-m10 | M10 hex nut, 16 across flats × 8.4: the flywheel weight | STEP · STL |
| nut-m12 | M12 hex nut, 18 across flats × 10.8: the flywheel weight | STEP · STL |
| nut-3-8in | 3/8 in hex nut, 14.29 across flats × 8.33: the flywheel weight | STEP · STL |
| nut-1-2in | 1/2 in hex nut, 19.05 across flats × 11.11: the flywheel weight | STEP · STL |
Plain text: sheet.txt · JSON: /api/geometry?object=nut-weighted-flywheels
How it fits
Goes in or on
Stirling shafts and rodsØ3 / Ø5 / Ø8 D-flat shaftsConnects to
Stirling linkage fittingsgamma crankshaft in the 625 stands
Tri-clamp power pistons and crank linkagecrank frame's Ø8 shaft
Rhombic drive kitlong Ø5 gear shaft
Alpha V-twin frame for two 10 mL syringesbehind the boss
Can-engine printed kitØ3 hub on the skewerAlternatives
Crank discs, connecting rods and flywheels for…plain printed flywheels
CDs, DVDs and hard-drive platters as flywheelsCD flywheel for the can engineAlso needed
Hex nuts, M2–M8steel nuts for the pockets
Set screws, M3–M8M3 grub in the hubIn these build lists
Gamma Stirling, 2 in tri-clampSoda-can gammaCan, tea light, foam, syringe, skewer, CD: the first engine, no budget.Beta Stirling, rhombic drive, 2 in tri-clampDisplacer and piston in one bore, two counter-rotating gears: the balanced one.LTD coffee-cup engineRuns on a cup of coffee: wide thin displacer, tiny piston.Alpha V-twin, two 10 mL syringesTwo syringes in a 90° V on one crank pin: the alpha with no displacer, checked s…Ross yoke alpha, two parallel 10 mL syringesTwo syringes side by side, one crank, a Ross yoke solved for 90° and near-straig…You might also need
Questions
How do I add weight to a 3D-printed flywheel?
Fill all pockets for inertia, alternate pockets for half, or one half only as a counterweight.
How heavy should a Stirling flywheel be?
For a 2 in tri-clamp gamma, Ø150 with a full set of 18 M10 nuts adds about 190 g and 7.6 kg·cm² of inertia; start there and remove nuts until it still carries through a cycle. Lighter wheels start faster; heavier ones run smoother.
Metric or inch nuts?
Either: the Ø120, Ø150 and Ø200 wheels come in 3/8 in and 1/2 in versions for US hardware-store nuts as well as M10 and M12.