Formula to predetermine length growth from thread rolling

[Patrick618]

Is there a formula to predetermine the linear growth from rolling a thread? I have a part made from 4340 steel that will have a 3/8-24 thread rolled for a length of 1-3/4" and I only have .006" tolerance on the overall length which I am afraid will get longer after the thread is rolled. The thread roll will be sublet and obviously be done after the blank has been produced so I must compensate for any growth on the blank.

 

[rob768]

With regards to the rolling process: There is some plastic deformation just below the threads surface, the rest is mostly elastic deformation, which means material is displaced, not compressed. The minor hardness difference in the shank compared to the threaded area at sufficient distnace from the actual threads suppoorts this.
My guess is that there will be lenghtening, since the total volume stays the same. The difference in volume being the basis foro the length change?
I'd go for a test. Roll a few and measure them before and after the rolling process. All others methods are educated geusses imo, and if this is so critical, a test is the only way to be sure.