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CDs, DVDs and hard-drive platters as flywheels
What are the dimensions of a CD and its centre hole? · Standard part · basis: ECMA-130 / ISO 9660 physical disc: Ø120 × 1.2 mm, Ø15 mm hole; hard-drive platters per the 3.5 in (95 mm) and 2.5 in (65 mm) form factors
Long Earth Society build part. Flywheels for the can engines; the hubs in the kit fit them to 5 and 8 mm shafts. The engines · all LES parts
- sizes
- 4 in table
Notes
- CD/DVD/Blu-ray: Ø120.0 mm, 1.2 mm thick, Ø15.0 mm centre hole, 16 g polycarbonate. Mini CD Ø80. The hole is held to +0.1 mm, so a printed Ø14.9 hub press-fits.
- 3.5 in drive platter: Ø95 × 1.27 mm (some 0.8–1.0), Ø25 mm hole, aluminium (older, 30 g) or glass (newer, do not drill). 2.5 in platter: Ø65 × 0.8, Ø20 hole. Mirror-flat, perfectly balanced: a stack of three 3.5 in platters on the printed hub is a 90 g, Ø95 flywheel.
- The hubs in the can-engine kit take a CD (Ø15 bore) or a 3.5 in platter (Ø25) onto a 5 mm or 8 mm shaft with a set screw. Two CDs glued with a 1 mm spacer are stiffer than one.
- A CD flywheel is 16 g at Ø120: it stores as much energy as a Ø60 × 10 mm steel disc, which is why the can engine runs on it.
Sizes
| disc | dia_mm | thickness_mm | hole_mm | mass_g |
|---|---|---|---|---|
| CD / DVD | 120 | 1.2 | 15 | 16 |
| mini CD | 80 | 1.2 | 15 | 7 |
| 3.5 in HDD platter | 95 | 1.27 | 25 | 30 |
| 2.5 in HDD platter | 65 | 0.8 | 20 | 7 |
Where the files are
Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.
| Wikipedia | Compact disc | web | CC BY-SA 4.0 (text) |
| Wikipedia | Hard disk drive platter | web | CC BY-SA 4.0 (text) |
| Long Earth Society | Engine builds (videos and write-ups) | 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
| cd-dvd-120 | CD / DVD / Blu-ray: Ø120 × 1.2, Ø15 hole (Ø15.0 +0.1) | STEP · STL |
| mini-cd-80 | Mini CD: Ø80 × 1.2, Ø15 hole | STEP · STL |
| hdd-platter-3-5in | 3.5 in hard-drive platter: Ø95 × 1.27, Ø25 hole (aluminium or glass) | STEP · STL |
| hdd-platter-2-5in | 2.5 in platter: Ø65 × 0.8, Ø20 hole | STEP · STL |
Plain text: sheet.txt · JSON: /api/geometry?object=cd-dvd-and-drive-platters
Fits with
Questions
What is the diameter of a CD centre hole?
15.0 mm (+0.1); the disc is Ø120 × 1.2 mm. A printed Ø14.9 mm hub press-fits.
What are hard drive platter dimensions?
3.5 in drives: Ø95 mm, 25 mm hole, about 1.27 mm thick (aluminium) or 0.8–1.0 (glass). 2.5 in drives: Ø65, 20 mm hole, 0.8 mm.
Is a CD a good flywheel?
For a can or test-tube Stirling, yes: 16 g at Ø120 mm beats a small solid disc; stack two for stiffness and glue a coin at the rim to balance.