Gear cutting basics help needed.

I have made two regulators in the past and I made my own fly cutters from broken centre drills and mounted in a cutter bar made from stock.This cutter bar can be mounted in the mill.In my case I had two revolving centres with the cutterbar mounted between centres with a pulley attached driven from a motor at the rear, as the lathe is not fast enough for a fly cutter.The Myford dividing head was set at an angle on a adjustable milling slide and driven over the cutter.I never bought any cutters for either clock.

Frank

Thanks John yes I have ER32 imperial and metric collets, 6mm bolt it will be, my old Acorn lathe doesn't do metric threads.

In response to Simon Williams 3, for involute gears using standard hobs (20 PA) the minimum number of teeth for satisfactory meshing is 10. However as for all gears with less than 20 teeth, the gear diameter would need to be increased above the usual (T+2)/DP.

I was told by an ex Smiths employee that, at one time, they made clocks using involute gears.

To accomodate the limitation on tooth numbers imposed by the involute system most clock gear trains would of course need to be redesigned.

As an aside, gear pumps have been made using gears with only 8 teeth but these were made using special involute hobs of 25 PA (?) with non-standard cutting depths.

Although clock and watch gears are referred to as Cycloidal, I believe they are only approximately so. For example, it seems unlikely to me that the inner part of the contact faces of 6 leaf pinions (the hypocycloids), which are straight in practice, are theoretically so.

But I'm no expert so please feel free to put me right.

Actually, the straight dedenda of both pinions and wheels are the only part of the so-called cycloidal tooth forms that actually are parts of hypocycloids! The addenda curves are circles or segments of circles.

If you use Mike Cox's spreadsheet for designing button cutters it's relatively easy to find non standard pressure angles that permit small tooth counts without undercut.

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True

… as noted in Mr Sparks’ essay, to which I referred earlier.

MichaelG.

Hi Ian

In horology a leaf is a tooth.

If you click on Wheel Cutters instead of pinion cutters you will be able to select what you need. Pinion cutters vary in shape according to the number of leaves (teeth) on the pinion. Wheel cutters will cut any number of teeth. As you are making latern pinons you do not require any pinion cutters. I've put a link to wheel cutters below if that helps.

I know there is a trend to advocate involute tooth shape for clocks but as you will deduce from the above there are practical advantages in using cycloidal not least that you only require ONE cutter for all wheel counts from 17 to infinity. Another is that fly cutters are simple to make.

**LINK**

regards Martin

For those curious about the Lantern Pinion: **LINK**

https://www.tec-science.com/mechanical-power-transmission/cycloidal-gear/lantern-pinion/

MichaelG.

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Edit: __ I’ve just found this : https://youtu.be/dCeBCR0-lr0

Part 4 is about making the lantern pinion

Edited By Michael Gilligan on 04/04/2022 09:20:40