I need to make a 12 tooth 20DP 14.5 degree involute spur gear.
I've cut plenty of low tooth count cycloidal clock gears, but this is the first time I've tried to make an involute gear. I started with a blank (12 + 2)/20 = 0.700 inch diameter, and mounted this on a mandrel on my dividing head. I then cut 12 teeth 0.108 inch deep with a new No 8 B&S type 14.5 degree involute gear cutter.
The resulting gear is not satisfactory, and does not mesh properly with other 20 DP gears I have (e.g. the change gears for my Myford lathe). The gear also looks odd compared to my Myford gears, in that instead of having flat-topped teeth, the teeth have sharp points rather like cycloidal clock pinions. It also looks for all the world as if the teeth on my gear would need to be undercut at the bases in order to mesh correctly, but clearly this can't be done with plunge- cutting cutter.
I'd be most grateful for some advice. The No 8 cutter is supposed to be suitable for gears with 12 or 13 teeth, but looking through some books just now I read that gears with so few teeth do need to be undercut. How is this possible?
TIA
Mike