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
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)
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
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
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.
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?
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.
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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