Gear DP Question

500mpxlcameraguy · Oct 16, 2020

Hi folks,
I have what should be an easy question for someone. I have a 9A which I occasionally use to make metric threads. I am in need of a 28 tooth gear and have seen one that is 21/32” in diameter putting it in between 18DP and 16DP. Does that sound like it will work on my 1962 lathe?
Thanks

johnoder · Oct 16, 2020

Something wrong there with the 21/32 - which is .656"

You add 2 to the 28 and get 30, and 30 divided by .656 = not quite 46 DP

An 18DP 28 tooth will be 1.667" OD

500mpxlcameraguy · Oct 16, 2020

Yup , 1 21/32” sorry about that.

500mpxlcameraguy · Oct 16, 2020

So I add 2 to the number of teeth before dividing? Then it comes out about right for 18DP.........Thanks!

bianiro · Oct 17, 2020

You have a few options for figuring out the diametral pitch, you can either measure the OD of the gear and divide the diameter by the number of teeth on the gear plus two.

Another option is to get a gear pitch gage, I picked up a Fowler gage from McMaster-Carr a few weeks back and it has helped me save time in figuring it all out, I'm rebuilding a 1941 heavy 10 and have a fair amount of gears I need to remake for it, so getting a gage seemed like a no brainer. Here's the gage I got: McMaster-Carr (Or if you wanted to order it elsewhere the Fowler model number is 52-470-140)

I also have a Solidworks gear generator file, if that's of any use to you I can send it to you.

Best of luck on your project!

500mpxlcameraguy · Oct 18, 2020

Thanks for your good information and kind offer. I think that I have the gears that I will need for now. (I know “That’s what they all say”) My SB usually has the threads on the QCGB that I need and with the “Plastic” conversion gear and a few extra from eBay, metric as well. The lathe is well warn but with a lot of tinkering and replacing the countershaft is fine for my needs.
I wish you the best in your heavy 10 rebuild.....sounds like a big project.

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