Need help on a project

Canus

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Mar 19, 2018
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176
Making a 5C collet holder for my 16" Southbend lathe. Can't figure out internal diameter to bore for threading this item. I know the spindle thread is 2-3/8"-6TPI. Best I have been able to come up with is approximately 2.196. Thanks in advance for any assistance.
 

Joe Pie

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Jun 17, 2020
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Making a 5C collet holder for my 16" Southbend lathe. Can't figure out internal diameter to bore for threading this item. I know the spindle thread is 2-3/8"-6TPI. Best I have been able to come up with is approximately 2.196. Thanks in advance for any assistance.
Calculating the bore diameter for internal threading is easier than you think. On most threads, metric and imperial, its the major diameter minus the pitch value. Metric example: M10 x 1.0 would require a 9.0mm bore. On imperial threads, such as your request, divide 1" by the number of threads for your pitch value, then subtract that from your major ( or outer ) diameter. This value puts you in the middle of the allowable range for your bore diameter for B class threads. To be safe, I always go a little bigger.
 

Bob Korves

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Jul 2, 2014
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Calculating the bore diameter for internal threading is easier than you think. On most threads, metric and imperial, its the major diameter minus the pitch value. Metric example: M10 x 1.0 would require a 9.0mm bore. On imperial threads, such as your request, divide 1" by the number of threads for your pitch value, then subtract that from your major ( or outer ) diameter. This value puts you in the middle of the allowable range for your bore diameter for B class threads. To be safe, I always go a little bigger.
Hey, Joe, Nice to see you on this forum. We hope you will be able to add lots more good posts to this useful forum. Thanks!
 
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