Advice on number of pinion leaves

[margolisd]

Hi guys. I’m trying to think this through. I’m restoring a vintage IWC. It has a tiny power gauge works which is hard to describe, but, long story short, two tiny identically sized pinions have broken against each other. Replacements aren’t available. I don’t have the right tools to cut pinions yet. But in my scrap I’ve found a couple I can use that are the exact same diameter. Only difference, they have 10 leaves rather than 12 as the originals have. Is there going to be any disadvantage to swapping them out to 10 leaf pinions if the diameters are the same and they mesh okay? What dictates the decision to make a pinion a certain number of leaves? Is it just the size of the pinion and the ease of cutting them?

[CaptCalvin]

Pictures would give us more to help form an opinion. But from what I can gather if they fit fine and they're 1:1 gear ratio I would think it would still function.

[nickelsilver]

A 10 leaf pinion the same diameter as a 12 leaf pinion means they are different modules. The 12 is a smaller module.

You're saying the two 12 leaf pinions were meshing with each other? That's odd, was this part of the differential? It would be lucky if two 12 leaf pinions had the same center distance as 10 leaf even if they are the same diameter, it could be though, or close enough to still work. The 12 leaf pinions would be weaker than 10 leaf for the same diameter.

If either or both pinions are mounted to a wheel as well no way it will work, as the gear ratio will be changed. If they are just transmitting motion from another gear, through each other, to another gear, the ratio won't change.

A pic or two or three would help.

[margolisd]

Thanks. This is probably the clearest thing to show what’s happening. I have marked both points where there are broken teeth. Both wheels are 1.39 with 12 leaves. And I propose replacing with wheels 1.39 with 10 teeth.

Just to clarify, on the right, I’m pointing at the wheel underneath that is a bit hidden in this picture.

 

Edited July 30, 2020 by margolisd

[nickelsilver]

Ah so it is 12 to 12, so the ratio won't change. If the 10l do mesh correctly it could work.

[margolisd]

Awesome! I’ll report back!

[nickelsilver]

Bear in mind though that a pinion is usually designed to mesh with a gear of several to 7,8, or more times its number of teeth. For pinions this small to mesh together the profiles are quite modified from "normal". Even so, this is a low power situation so things are more forgiving.