Make lathe gears easily

How to cut spur gears on a metal lathe

lathe change gears

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Gears for lathes are hard working parts which can easily be damaged, and are subject to a lot of wear and tear.  A lathe that gets used a lot is bound to crunch a gear at some stage.

You may need a replacement change gear, want to fit a reverse tumbler, or a different sized gear to cut a thread pitch not included in the standard set.

You might just want to make a gear to slow down the leadscrew for a finer cut.

Spare parts for lathes can be hard to get, or non-existant locally.  If a gear has to be made in a machine shop or imported from overseas it can be an expensive exercise.

You can try and cut your own gears, but that requires lots of skill and equipment, right?

Cutting gears is portrayed as a black art, only experienced machinists need apply, and only those with expensive milling machines, fancy dividing heads, gear hobbs, and mysterious formula to calculate pressure angles and the like can do it.

But that's not so.  Spur gears are easy to make, and all you need is a lathe and a few pieces of basic equipment.

I made the two smaller gears below - examples of the quality possible.

home made gears

Both are 30 tooth gears approx 31 mm in diameter.  An original factory gear is shown on the left for comparison.

I used a home made fly cutter for the brass one, and a commercially made involute cutter for the cast iron gear on the right.  The cast iron gear is near perfect.

All this was done on my cheap Chinese lathe and without spending much money.

The quality of the gear will depend upon the amount of care and accuracy taken.

After accidentally damaging some lathe gears, and finding that replacements were either unavailable locally or hideously expensive from overseas suppliers, I researched the subject thoroughly to see if I could make my own.

After a bit of head scratching over what I could do with my limited amount of equipment, I  eventually made my first useable gear out of some scrap aluminum.

I then moved on to make the brass ones below, using the system described in the following pages.

brass gears

These turned out very well, and have less run out than the Chinese factory originals.

Since then I've also made gears from cast iron, without a problem. 

While cutting gears may seem a bit daunting to the average hobbyist, it's really not that difficult, and it's quite satisfying to see your homemade gears in action.

This is the sort of quality you can easily achieve with a bit of care.

Provided you're willing to spend time to set up the lathe to do this, there is no reason why you can't cut your own gears. 

You must however be absolutely precise.  There is NO room for error.

An accurate indexing system is essential to get correct tooth spacing.

I didn't have a dividing head, but no problem, you can easily make an indexing disc out of a printed pie chart glued onto cardboard to get the job done.  This is described further on.

This will index a gear equally as well as any expensive dividing head, if used correctly.

Combined with an accurately profiled cutter, you should be able to produce a good quality gear every time.

Here's a recent video showing how easy it is.

Plus an older one.

You WILL need a vertical mill slide attached to the cross slide to use this method.

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