Proportional compasses (sliding pivot in slotted legs) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/proportional-compasses-mechanism/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Xem Studio design following Brown No. 409 (1868)
Catalog version: 2026-10-20

Sizes: see table below
- Two pointed legs cross on a pivot that sits in a slide block running in a slot in each leg: the points at the two ends open in the ratio of the arm lengths either side of the pivot, so a distance taken with one pair of points is copied at a fixed scale by the other.
- Drawn with the pivot 26.67 mm from the legs' centres: arms 106.67 and 53.33 mm, ratio 2 : 1, legs at 20°. Moving the slide to the centre gives 1 : 1; a set screw (not drawn) locks it.
- Brown's No. 409 (proportional compasses with a sliding pivot and scale).
- Parts (each has its own page): proportional-compass-leg-160-slot6, slide-block-12x6, dowel-pins-metric.
- Brown's movement No. 409 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

parameter  value
legs  2 × 160 × 14 × 5, slotted
pivot offset drawn  26.67 mm
ratio drawn  2 : 1
slide blocks  2 × 12 × 6.2 (catalog)

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. 409: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_409.html

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