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Problem Cutting 12 tooth Spur Gear

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

Reply to
mikecb1
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Hi Mike

On the face of it, It sems that you have it all done correctly, I can only suppose that you have made an error somewhere. Lets go through it all, firstly check the blank OD , if OK then check the dividing head, is it set for the right number of teeth, as this could lead to the results you have got, Alternatively, have you gone deeper than 108",again you an check this on the gear you have cut. If all this checks out OK you need to look at the cutter, offer it up to a similar cout wheel from the Myford chain and see if it could have cut the teeth. I am happy to have a look at it all if you get them to me Peter

Reply to
petercolman45

Peter

Thank you for your advice. I went through everything today, and as you predicted I made a mistake. Somehow I managed to cut the gear too deeply. Only .010" or so, but enough to ruin the meshing. I've just cut another gear to the correct depth (in my caution it's actually a couple of thou under), and it meshes fine with my Myford gears. It also looks right, with flat tops on the teeth!

Thanks again

Mike

Reply to
mikecb1

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