I created an M12 (pitch 1.75) threaded rod in Solidworks 2019. Originally, I needed to do a length of 350 mm and because I had chamfered the ends, my rod was threaded about 346 mm, essentially centered. I had to reduce the length by 15 mm, so I successfully reduced the length of the rod and the thread by 15 a piece. This often took many minutes to rebuild and sometimes it failed due to geometric errors. It only took me under 5 tries so I wasn't terribly worried, but notably all I was doing was changing numbers in the thread and boss extrude feature. To my estimation, there was no significant different to the action I was performing, just whether or not I would get the error. I had to do another drop of 15 mm so I went through the same process. This time I have been unlucky and have tried perhaps 20 times unsuccessfully to reduce the threading length. I tried a number of things that all failed.

1. Changing the length of the thread (as detailed above).

2. Removing the thread and remaking it.

3. Doing an extruded cut.

4. Doing an extrusion.

It seemed to have better performance at smaller thread lengths say 80 mm, but I'm not interested in having a file with 4 threads in it. My preference is to have it done once.

My question is why would geometric conditions prevent rebuild even though I am only changing the length of the thread? My greater question is how might I successfully complete this threaded rod?