Wheel and Pinion Depthing

Ok, I've took some meshing pictures. It wasn't easy. I had to take dozens to get two adequate pics.

These ar at the tightest mesh that still allows free running. In practice, I'd probably increase it by a couple of thou.

By the way, 12T pinion, 73T wheel.

Steve

This close up photography does not flatter the finishing on my tools!

For scale, the runners are 2mm diameter.

By the look of those photos the wheel tooth form is all wrong for a clock

A good reference book is Michael Wild clock wheel and pinion cutting, it's expensive but the definitive book on the theory and practice of cutting wheels and opinions for clocks.

Good photos though !

Regards

Derek

Good photos, Steve … but I don’t like the look of that meshing

If you send me your eMail address by personal message here, I have a PDF of chapter1 of Gears for Small Mechanisms, which you might find of interest.

The book is excellent, but rather dated … grab a copy if you see it cheap, but I doubt you would need most of it.

MichaelG.

I should of made clear that these are for (slow) motion work. The 73 T wheel revolves one a year. I'm sure that involute is legitimate for this and not "all wrong for a clock".

I have had the Wild book for some time now and have copied quite a few of the fixtures and fittings featured. I also have the Gears for Small Mechanisms.

It's not so much the theory I'm so concerned with. I have a set of Mod 0.3 cutters and it's all about making the most of those.

I would love to do everything in cycloidal with Thornton cutters but £££.

Steve

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With the greatest respect, Steve … I think that may be what’s causing your depthing difficulty

MichaelG.

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Edited By Michael Gilligan on 12/09/2022 23:44:25

Have you tried this, Steve ?

**LINK**

http://www.hessmer.org/blog/2020/09/27/online-involute-spur-gear-builder-v2/

… from that very clever chap, Dr. Rainer Hessmer

MichaelG.

I have used that site before. Here's what it shows for the gears in question -

The thing is, I don't have a depthing difficulty as such. The gears run smoothly and freely with little backlash and I can live with the extra depthing distance.

But I don't like the look of the tooth profile on the pinion.

Steve

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I’m really sorry to labour this, Steve … and I will leave you in peace after this posting:

You do have ‘a depthing difficulty as such’ : Your pinion is not sitting at the right depth in the wheel.

Just compare your photo with the drawing.

If you are not bothered about the proper involute action, then the teeth could be any old shape you like, and you can run them at any depth you fancy. … but in that case, your opening question would seem irrelevant.

MichaelG.

No problem Michael, I appreciate it. I need all the help I can get!

What bothers me about the drawing is that there appears to be no clearance or play. There are 5 points of contact including one on the root of the pinions. It also seems that the tooth depth is only 2 x Mod.

I scanned the wheel and pinion again and overlaid the outline from the drawing to see how profiles compare -

They are a lot closer than I thought.

Steve

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Although in practice it is impossible to achieve, that is hypothetically correct : That’s what I had in mind when I wrote ‘the proper involute action‘ … in a perfect world the action would be pure rolling without scuffing.

Life, of course, is not perfect, but it should be possible to get closer than your current depthing.

MichaelG.