I'm trying to thread mill a 4-pitch ACME thread with a 5-pitch tool (on a horizontal machining center). The program is correct. I'm wondering if the gage is. The angle is there on the tool (29 deg included), but the width of the tool is just smaller than a 4-pitch would be. I'm cutting to the theoretical major diameter, then taking a couple passes at different Z-depths to widen the thread, which I thought would be easy and make it into a 4-pitch just like that. I was wrong. What is happening using this method is the NO GO gage goes before I can get the GO gage to go. How is this possible? And is there any reversing the NO GO from going to not going, once it goes? Or is that it? Once it goes, the thread is forever going to be over size?

This is very frustrating, as it seems like it would be such an easy thing to do (making a 4-pitch out of a 5-pitch ground tool), but it's not working and I don't have any idea why. So, thanks for any help.

Btw, I hope I'm in the correct forum. There are so many, I didn't know if I should be on the tooling part or programming part or what. So I picked this one lol.

Thanks.