I've been slowly retrofitting a MaxNC mini mill that was all clapped out and had V screws over to acme screws with anti-backlash nuts. Of course nothing is easy about it. I just finished milling the Z axis slide for a mounting block for the nut and making the mounting block. Due to limited space I find myself having to use 6-32 cap screws for a couple things. I just happen to have a box of 6-32 stainless screws leftover from another project. Some of the holes tapped perfectly the first time, but that nice little mounting block I spent most of the day figuring out how to make and cutting between real work grabbed ahold of the tap and snapped it over its proverbial knee like a pretzel stick.
It only took me an hour to make another mounting block.
Now I'm paranoid about snapping another tap. I know 6-32 is tough to do by hand so I was wondering about options. Maybe going with a forming tap instead of a cutting tap. I looked up a table or two and there is a big difference. #36 drill bit for a regular cutting tap at .1065" diameter vs .125" according to one table when using a forming tap. That's a lot more material removal. I know. I know. Its just aluminum threads, but what kind of difference in strength are we talking about for the finished threads?
The holes that mount the block to the slide are done, now I need to tap the holes that mount the nut to the block.