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
Reply to
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)
Reply to
Don Young
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
Reply to
petercolman45
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
Reply to
Steve
wrote
How do you avoid this with a 1:2 ratio?
Henry
Reply to
Dragon
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.
Reply to
Erik Olsen DK
Thanks Erik - I can stop banging my head on the wall now, I just couldn't spot the trick and there it is!
Steve
Reply to
Steve
If you want lightweight, quiet gears how about tufnol? Russell.
Reply to
russell
Thanks Eric. I missed the fact that Peter was probably considering the two stage arrangement. Henry
Reply to
Dragon
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?
Reply to
newshound
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.
Reply to
russell
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.
Reply to
Steve R.
The Ford V4 & V6's in the 1960 had a camshaft Tufnol gear. Ben
Reply to
Ben
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
Reply to
Steve

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