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Worm and Worm Wheel: a Steel Screw and a Hobbed Bronze Wheel
Thorsten Hartmann · CC BY-SA 3.0
Martin

Created by

Martin

14. October 2026NO
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Worm and Worm Wheel: a Steel Screw and a Hobbed Bronze Wheel

A worm is a screw that drives a toothed wheel at right angles; with a single-start worm each turn moves the wheel one tooth, so a 30-tooth wheel gives 30:1. Cut the worm on a screw-cutting lathe, make a hob that is a copy of it with cutting edges, gash the bronze wheel on the dividing head, then run the hob through it to finish the teeth. The picture: a worm shaft with its bearings and a hobbed bronze worm wheel from a gearbox.
Advanced
Three to four days

Instructions

1

Cut the worm

Turn the steel bar to the worm's diameter and set the lathe's change gears to the axial pitch (π × module). Cut the single-start thread with a tool ground to the tooth form, checking it with the gauge.

Materials for this step:

Mild Steel Round BarMild Steel Round Bar1 piece

Tools needed:

Metal LatheMetal Lathe
Turning Tool Set HSSTurning Tool Set HSS
Thread GaugeThread Gauge
Vernier CaliperVernier Caliper
Cutting OilCutting Oil
2

Make the hob

Cut the same thread a little oversize on tool steel, file four or more lengthwise flutes across it to make cutting edges, back off behind each edge, then harden and temper it.

Materials for this step:

Octagonal Tool Steel BarOctagonal Tool Steel Bar1 piece

Tools needed:

Metal LatheMetal Lathe
Metal FileMetal File
Blacksmith ForgeBlacksmith Forge
Quench BucketQuench Bucket
Safety GlassesSafety Glasses
3

Cast and turn the wheel blank

Melt bronze in a crucible, cast a round blank, and turn it on a mandrel to the wheel's diameter with a hollow rim to wrap the worm.

Materials for this step:

Bronze IngotBronze Ingot1 kg
CharcoalCharcoal1 as required

Tools needed:

Blacksmith ForgeBlacksmith Forge
Clay Crucible - RefractoryClay Crucible - Refractory
Crucible TongsCrucible Tongs
Ingot MouldIngot Mould
Metal LatheMetal Lathe
Mandrel RodMandrel Rod
Welding GlovesWelding Gloves
4

Gash the teeth

Mount the blank on the dividing head with the cutter path set at the worm's lead angle and cut a slot for every tooth, nearly to depth.

Tools needed:

Milling MachineMilling Machine
Dividing HeadDividing Head
Cutting OilCutting Oil
5

Hob to shape

Run the hob in mesh with the gashed blank, free to turn, feeding it in gradually to full depth: it drives the blank round and generates the true tooth form.

Tools needed:

Milling MachineMilling Machine
Worm HobWorm Hob
Cutting OilCutting Oil
6

Sizes for a 30:1 set

Loading Jupyter Notebook...
7

Limits

Worm drive principles, gashing and hobbing are as Wikipedia describes them; the module, tooth count and making the hob from the worm's own thread are ours. A single-start set like this is usually self-locking, which depends on lead angle and friction.

Materials

4

Tools Required

17

This blueprint makes

Thumbnail
Placeholder

Worm and Worm Wheel Set (Steel/Bronze)

Free

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CC0 Public Domain

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