Pitch Diameter on Custom Threads

I don't understand the question, the pitch is calculated by threads per inch, if you make a non standard, what do you need a program to do?

The thread pitch diameter I have, what I am looking for is the best fit wire for a modified buttres thread with a 45/90° angle.I was looking for some software that will calculate wire size for custom threads. I hope this is a bettr discription of what i am looking for and thank you for the response.

Ah-now I understand. This is a very easy matter for any CADD programme. Just draw the threaded section as perfect size and by trial draw circles (they represent the measuring wires) tangent to the flanks until they are above the major diameter and as near the pitch diameter line as possible. "Measure" over the circles and you have your perfect size. I would try to select a circle diameter of "even" size, say 0.100", 0.150", 1,0mm, 2,5mm etc.. And that's an easy way to determine a simple measurement for pitch diameter.

But in the real world, a quick "over the wires" measurement will not reveal whether you have accurate flank angles, and a flank angle shift of a degree or so will affect your indicated dimension a bit. I do not know what size of thread you are concerned with. That is where wire measurements alone will not tell the whole story. You could use an optical comparator or CMM to verify the angles. If you can easily verify that one (1) flank is indeed 90 degrees, then the other can be verified by using wires of different diameters after calculating what would be the shift per degree of error of the 45-degree flank.

In closing, this has an easy solution through use of any of the common 2D CADD programmes out there. Just make sure the CADD is set to the fine resolution that you need.

Best Regards,

Ing. Robert Forbus

If I understand your question correctly, the information you seek can be sourced from a handbook such as Machinery's Handbook. The pitch diameter of any given nominal size will depend on that nominal size, the chosen pitch, the class of fit, and lastly, the method of manufacture. All of that information is available there. If a particular pitch diameter (and its tolerance) is not listed for a certain nominal size, it can certainly be interpolated from the other values there.

I have a home-made MSExcel programme that I wrote long ago for calculating thread characteristics, but it is more for design use than practical application. I am not aware of any thread software or shareware that is available for your purpose-but it may well be out there.

Best Regards,

Ing. Robert Forbus

This program might be very useful to you, though it doesn't handle the modified buttress you describe. It will do calculations for 7 x 45 and 3 x 30 buttress, as well as many other thread types.

http://closetolerancesoftware.com/METhreadPal.html