Gearing help needed

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Cogsy

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I've just received my plans for the Upshur farm engines and I'm planning my build before I start making chips.

The plans call for a set of 30 tooth and 60 tooth cam gears in either brass or steel, but in very small diameters (roughly 17mm and 32mm ~ 0.625" and 1.25"). As I will be constructing my own 'hob' cutter to cut these gears, I'd prefer to use a larger module, for ease of making the cutter. A module 1 would give me the correct diameters (close enough) and the same ratio, but with only 15 and 30 teeth.

I'm thinking each tooth will have increased load because less teeth will be engaged, but the teeth are bigger and I assume stronger. I'm wondering if my selection has a chance of working, or if I really need the 30 and 60 tooth gears.

Any advice greatly appreciated. Thanks.
 
I don't think I'd go as low as a 15t gear for it - your best bet would probably be to try and work a 20/40 pair in. Or even a 19/38.

In fact the 19/38 might work out very close in 40 dp

2388859950105506259S500x500Q85.jpg
 
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As tel says 15T is a bit chunky

20/40 would suit 32dp
25/50 would suit 40dp and both keep the same PCD.

J
 
Nice looking gears Tel. I wish I had a couple ;)
 
Being that you're going to make your own hob/cutter why not just make it to what the drawing calls for. That would make life simpler for the fact that you wouldn't have to change center spacing or adjust pushrod lengths to accommodate different pitch gears. As far as the size of the pitch 32, 48, 64, these engine don't required a lot of power transfer so I prefer to use a finer pitch that way you can change your timing in smaller increments by moving one tooth at a time.
gbritnell
 
Those gears look about perfect for the job - I'll PM you my address shall I? :p

If I've done my calcs right (and my little bit of knowledge isn't wrong), I think a 20/40 combo in 0.8 module or 31.75DP, should give me PCD's of 16mm and 32mm, for a shaft centre distance of 24mm. The plans have a centre distance of 23.81mm, which I can easily change, so that seems to be the way to go.

The hob would be a heck of a lot easier for me to make in 31.75DP than in 48, so that works out as well.

Thanks for the great responses. I didn't want to waste 3 or 4 days making a hob and gears to find out they wouldn't work.
 
Being that you're going to make your own hob/cutter why not just make it to what the drawing calls for.

What you're saying makes perfect sense, it's just that I don't think I've got the skills necessary to make a hob that fine. I might be fooling myself, but I think I can get closer to correct working in the slightly larger scale of 32ish DP rather than 48.

I'm now thinking I might start by making the hob and gears first. If they work out, I might as well have a go at making a 48DP set too. I'll just make sure I have a working set before I lock in shaft centre distance.
 

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