Pinion between a fixed and a free rack (travel doubler) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/pinion-between-racks-doubler-mechanism/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Xem Studio design following Brown No. 118 (1868)
Catalog version: 2026-10-20

Sizes: see table below
- A pinion turns on an axle carried by a rod. Below it is a fixed rack, above it a rack free to slide. Moving the axle a distance d rolls the pinion on the fixed rack, and its top, moving at twice the axle's speed, carries the free rack 2d: the stroke is doubled with no gearing ratio.
- Module 1, 20-tooth pinion, racks with pitch lines 20 mm apart (one pitch diameter); drawn with the axle 6.28 mm (two pitches) along and the free rack 12.57 mm along. The free rack's own guide is not drawn.
- Brown's No. 118 (pinion on the connecting rod between a fixed and a movable rack).
- Parts (each has its own page): gear-rack-m1-120-full-depth, spur-gears-module-1, pinion-carrier-rod-100-bore6, dowel-pins-metric.
- Brown's movement No. 118 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

parameter  value
pinion  20 T, module 1
racks  2 × 120 mm, pitch lines 20 mm apart
ratio  free rack = 2 × axle travel
rod  100 mm

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. 118: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_118.html

Free files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/pinion-between-racks-doubler-mechanism/index.json
API: https://xemstudio.com/api/geometry?object=pinion-between-racks-doubler-mechanism