How to calculate pitch diameter of external threads

[Watco]

How do you calculate the minimum pitch diameter for external screw threads as listed in the machinists handbook table 3 in the threading section.

 

[chicopee]

To be exact, the pitch dia.= major dia. - 1/2(major dia-minor dia.). Having said that, there are tolerances for min. and max values for major and minor diameter of threads, therefore, there will be min and max values for the pitch dia.

Pitch dia.(max;min)=(1/2)( major dia.(max;min)-minor dia.(min;max). I just derived this last equation but you may want to carry it out with real numbers and see how it compares w/ your Machinist's Handbook. a

 

[Watco]

Ok, then how do you calculate the minumum minor diameter? So that I may apply it to your formula. The minumum minor diameter is not listed in the handbook.

 

[roseda]

For metric threads, the formulas are given on page 1765 (26th Edition)

Perhaps the Unified threads use similar formulas. I would suggest trying to get hold of a copy of the ANSI standard.

 

[cobb]

Are you using thread wire's if so what is the thread size?

Cobb

Scott Cobb
CSM Manufacturing, Inc
csm-mfg.com