Cutting Spur Gears

Having turned, milled, annealed and hardened and tempered, I now need to add cutting some spur gears to my CV.
I have a mill and decent rotary table, so I'm assuming that I just need to
buy the appropriate gear cutter and work out the "angle of dangle". This, like most of the things I do, will be fairly rare event. The design I'm currently working on suggests I need to make two 12 tooth and two 24 tooth module 1 gears cut with a 20deg pressure angle (that is to say bog standard stuff - but given my hobby is learning to make things, buying them misses point!).
However, one question I'd like some help with is the material to use - the gear chain of events is a 12 tooth spur cut in EN8 and hardened will drive a 24 tooth gear on a countershaft. The countershaft also has a 12 tooth gear which then drives the final 24 tooth gear, to achieve a 4:1 reduction. This is being used to drive the valve timing cam in a 15 cc model engine (don't worry about 4:1 and four stroke -it's a trick I found on t'internet). Given I want minimum weight and to minimise gear noise what materials can I use in the gear chain after the driver spur (typically running at 5000rpm)?
Steve
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Only from what I have read about gears, I think you might want to rethink your tooth counts. A quiet high speed 12 tooth pinion might be difficult to make. I think I would consider using more teeth.
Don Young (USA)
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Firstly, the tooth count will lead to the same teeth on the gears engaging with eachother, this is not good practice and it would be better to get away from 12/24 tothe ratio, secondly I agree that 12 teeth is a little low for a tooth count for a reliable set up, so look at altering the module (or DP) to give a minimum of 14 teeth on the pinion. As to material, I would go for hardened steel for the smaller gears and possibly for the larger. If I can help any more PM me Peter
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wrote:

Firstly, the tooth count will lead to the same teeth on the gears engaging with eachother, this is not good practice and it would be better to get away from 12/24 tothe ratio, secondly I agree that 12 teeth is a little low for a tooth count for a reliable set up, so look at altering the module (or DP) to give a minimum of 14 teeth on the pinion. As to material, I would go for hardened steel for the smaller gears and possibly for the larger. If I can help any more PM me Peter
Thanks Peter. I'll jig around with the design and see how I can apply these comments.
Steve
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How do you avoid this with a 1:2 ratio?
Henry
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Dragon wrote:

The overall two-stage gear ratio should be 1:4. This can be done for instance with a 17 tooth gear driving a 28 tooth gear and that axle a 14 tooth gear driving a 34 tooth gear.
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Erik Olsen
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wrote

Thanks Erik - I can stop banging my head on the wall now, I just couldn't spot the trick and there it is!
Steve
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wrote

Thanks Eric. I missed the fact that Peter was probably considering the two stage arrangement. Henry
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If you want lightweight, quiet gears how about tufnol? Russell.
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If you want lightweight, quiet gears how about tufnol?

Excellent stuff, British motorbikes used to use it for magneto drive gears, but it would need to be *big* to cope with spring operated valves. Maybe OK for desmo?
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The 1930 Talbot sports car I used to own used tufnol gears for the camshaft drive, although I must admit that the racing team used steel gears when they won their class at Le Mans.
Russell.
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wrote:

Didn't the old flathead Morris Minor engine use a Tufnol timing gear on the camshaft? Perhaps it was the Oxford, or both models??
Steve R.
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wrote:

The Ford V4 & V6's in the 1960 had a camshaft Tufnol gear. Ben

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The cylinders are only 5cc each and the spring will be wound from 24swg to give you an idea of loading. Current design has the gears at 6mm wide.
Steve
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