# Reversing-screw drum and traverser (uniform to-and-fro traverse)

> How does a level-wind drum move a pin back and forth?

- Category: Mechanisms › Screws
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 108 (1868)
- Page: https://xemstudio.com/objects/reversing-screw-traverse-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=reversing-screw-traverse-mechanism · Plain text: https://xemstudio.com/objects/reversing-screw-traverse-mechanism/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files Xem Studio Design License (free to use and sell from, not to redistribute as files: https://xemstudio.com/license/)
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- 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.

## Sizes

| 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 |

## Where the files are

- Henry T. Brown (1868, public domain): [Five Hundred and Seven Mechanical Movements — scan on archive.org](https://archive.org/details/fivehundredseven00browiala) — web — Publisher's page; dimensions are facts
- 507movements.com: [Brown's movement No. 108: figure, his text and an animation](https://507movements.com/mm_108.html) — web — Publisher's page; dimensions are facts

## Free STEP/STL (1 parts, Xem Studio Design License, Xem Studio)

Index: https://xemstudio.com/files/hardware/reversing-screw-traverse-mechanism/index.json · license: https://xemstudio.com/files/hardware/reversing-screw-traverse-mechanism/LICENSE.md

- reversing-screw-traverse-mechanism-assembly: [STEP](https://xemstudio.com/files/hardware/reversing-screw-traverse-mechanism/reversing-screw-traverse-mechanism-assembly.step) · [STL](https://xemstudio.com/files/hardware/reversing-screw-traverse-mechanism/reversing-screw-traverse-mechanism-assembly.stl) — Assembled mechanism, all parts placed at one pose (STEP keeps each part separate)

## Questions

**How does a level-wind drum move a pin back and forth?**

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.

## Fits with

- [Reversing-groove drum Ø30 × 90: crossed right- and left-hand grooves, pitch 30, 5 wide](https://xemstudio.com/objects/reversing-groove-drum-30x90-p30/)
- [Traverser block 16 × 28 × 16: Ø5 pin hole (radial) and Ø6 guide-rod bore](https://xemstudio.com/objects/traverser-block-16x28-pin5-guide6/)
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/)
- [Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long](https://xemstudio.com/objects/linear-shafts-h6/)