On Nov 1, 10:17*pm, "Bob La Londe" wrote:
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.

One of these: http://www.use-enco.com/CGI/INSRIT will greatly improve
your results over doing it entirely by hand. Last week, I busted a
6-32 in a piece because I was too lazy to pull out the tapping machine
for just one hole. Then I got to make the widget* over from scratch.
Tapped it with the machine, no problem.

* said widget is an adapter for my Pace desoldering station to hold
the smaller tips. Pace wants $70 bucks (+ shipping) for something that
took me maybe 15 minutes (the second time) and a couple of inches of
7/16" drill rod. It's very nice to be able to make this stuff.