# double-check my numbers, please!



## wawoodman (Sep 14, 2012)

I'm going to try to make a back plate for my 10K. The spindle thread is 1-1/2 x 8. 

I measure the major diameter of the threaded portion at 1.497. I don't have thread wires, but I read that you can also check the pitch (? size?) with a single pin. With a .077 pin (a drill bit shank) I measure 1.519. I'm not even sure what this measurement means. I measure the distance from the tip of the spindle to the front of the shoulder at .875.

Any comments or help will be appreciated!~


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## Tony Wells (Sep 14, 2012)

The way to do this is to do all the calculations as though you were using a standard 3 wire measurement, then subtract the over-wire measurement from the actual major diameter. This divided by 2 will give you the addendum for using a single wire. Add this back to the actual major and you will get the single wire target. When I get out to the shop in just a bit, I'll run the numbers to see what I come up with. There will be a high and low range.


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## Bill Gruby (Sep 14, 2012)

Basic Pitch Diameter for 1 1/2-8 is 1.4188.

"Billy G" )


http://www.portlandbolt.com/Documents/Portland-Bolt-Thread-Pitch-Chart.pdf


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## Tony Wells (Sep 14, 2012)

1.500-8 UNC 2A thread should have a major between 1.4978/1.4828 

With 0.077 wires, the over-wire dimension should be 1.53935/1.53205

So, using those dimensions we come up with an addendum for one wire of 0.0227 using mid tolerance for the major and the PD.

So to get pretty close to the actual PD of your spindle, measure the actual major diameter and single wire and subtract 0.0227 and you will get the PD for the thread. Not sure why you need it unless you are making a dummy spindle copy for a gage.

Keep in mind that this is a rather indirect way to get there, and is subject of small errors, probably insignificant for what you are doing.


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## wawoodman (Sep 16, 2012)

Thanks!


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