sun/planet gears

[peter warnerParticipant @peterwarner63189]

At the risk of looking stupid,how do I calculate the diameter of a gear with the teeth on the inside diameter?I have cut small gears before-where you add 2 to the DP to get the outside diameter of the blank,how does it work when the teeth are on the inside?

[peter warnerParticipant @peterwarner63189]

how to calculate diameter

[Brian WoodParticipant @brianwood45127]

Hello Peter,

Not silly at all. To find inside diameter for the blank, subtract 2 and divide by DP.

Regards

Brian

[Sub MandrelParticipant @submandrel]

Brians formula is correct. I'm not sure how you design the cutter profile, however. I do know that you will have to plane the ring gears unless they are very big.

If it helps, the general principle is to design gears just by drawing the pitch circles (each of which should have a diameter of number of teeth/DP. If designing with a compass or moving circles around in a cad program the pitch circles should be set out so they touch each other with no gaps or overlaps. If doing it the 'scientific way' the centre distance between gears is (teeth in gear 1 + teeth in gear 2)/(2 x DP).

For sun and planet gears inside an internal ring gear, the PCD of the ring gear is:

PCD ring gear = PCD sun gear + 2*PCD planet gear = (teeth in sun gear + 2*teeth in planet gear)/DP

My head hurts now…

Neil

[peter warnerParticipant @peterwarner63189]

Thanks Neil,I think I will need to plane the ring gear.

Pete.

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