Reversing-screw drum and traverser (uniform to-and-fro traverse) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/reversing-screw-traverse-mechanism/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Xem Studio design following Brown No. 108 (1868)
Catalog version: 2026-10-20

Sizes: see table below
- A drum carries a right-hand and a left-hand helical groove that cross: a pin held in a block on a guide rod follows one groove up the drum and, at the end, is turned into the other and brought back. Uniform rotation gives uniform straight-line travel in both directions with no reversal of the drive.
- Here pitch 30 mm, two turns each way: 60 mm of travel per two drum turns. Drawn with the pin 150° into the right-hand groove, 12.5 mm up its traverse, in the 5 mm groove with its end 0.5 mm off the bottom.
- Brown's No. 108 (uniform reciprocating rectilinear motion from uniform rotary motion, by a cylinder with reversed threads); the same pair driven from the rod is his No. 167.
- Parts (each has its own page): reversing-groove-drum-30x90-p30, traverser-block-16x28-pin5-guide6, dowel-pins-metric, linear-shafts-h6.
- Brown's movement No. 108 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

parameter  value
drum  Ø30 × 90, Ø5 bore
grooves  RH + LH, pitch 30
traverse  60 mm per 2 turns, each way
pin  Ø5 dowel
guide rod  Ø6 × 150

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. 108: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_108.html

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