Face spiral (scroll) disc, pitch 3.14 (module 1), r 20 → 46.39, Ø100 × 6 — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/face-spiral-disc-m1-r20-8-4turns-d100/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Xem Studio design following Brown's figure (1868); true size, no printing allowance
Catalog version: 2026-10-20

Overall (mm): length 100.0, width 100.0, height 8.25
- A Ø100 × 6 disc with one raised Archimedean spiral rib on its face: radial pitch p = π m = 3.14 mm, from radius 20 to 46.39 (8.4 turns), Ø8 bore. The rib's radial section is the basic rack of module 1 (20° flanks, πm/2 thick at its pitch height 1.25 mm above the face, top at 2.25 mm): seen by a toothed part standing over the face, the rib is a rack that advances p per turn of the disc — a worm unrolled onto a face.
- Swept along the spiral with the profile kept upright and normal to the path; the bottom of the rib runs 0.5 mm into the disc so it is one solid.
- Xem Studio design following Brown's figure; true size, no printing allowance (apply your own to the mating features).

dimension  value
pitch p  3.14 mm (module 1)
spiral  r 20 → 46.39, 8.4 turns
rib height  2.25 mm above the face
disc  Ø100 × 6
bore  Ø8

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Henry T. Brown (1868, public domain): Five Hundred and Seven Mechanical Movements — scan on archive.org — web — Publisher's page; dimensions are facts — https://archive.org/details/fivehundredseven00browiala
- 507movements.com: Brown's movement No. 99: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_099.html
- Xem Studio: drawing — web — Publisher's page; dimensions are facts — https://xemstudio.com/objects/face-spiral-rack-feed-mechanism/

Free files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/face-spiral-disc-m1-r20-8-4turns-d100/index.json
API: https://xemstudio.com/api/geometry?object=face-spiral-disc-m1-r20-8-4turns-d100