# How to scale up a gear's diameter, increasing number of teeth and keeping teeth size constant?

I'm trying to use a gear system to run a rotating circuit board which will be attached to the larger of two gears.

I have a set smaller gear for the rotation which has 0.350" diameter gear with 15 teeth and Pitch Diameter of 0.312". Obviously I need to keep the teeth and gaps the same.

My gear which will have a circuit board seated onto it has an outer diameter of 2.7"

What I have been doing has resulted in the tooth thickness being too large, or the width of space being too large, resulting in gear slap or gear slippage. Suggestions?

• What exaclty have you been doing?
– mart
Mar 16, 2021 at 20:55
• I've been sketching the teeth from the gear I am using to rotate the heatsink. I then have been putting that onto the heatsink and then doing a circular pattern. I'm wondering if there is mathematical way to do it since I can't find anything on Google. Mar 16, 2021 at 21:18
• Any gear pair with the same diametral pitch (module for ROW) will have the same size teeth. You can scale up the diameter from that.
– jko
Mar 17, 2021 at 12:34
• If you have a set tooth size, then the circumference of the new gear is the old circumference times the new tooth count ratio to the old tooth count. Are you trying to create software to do this, or free-hand a drawing? A machinist can make a gear with any proper integer count of gears for a set diameter and doesn't need an accurate to scale drawing to do it. Mar 19, 2021 at 17:42