Made a tip for my dial indicator this morning. This is the smallest thread I've ever cut! Research says that most indicators have a 4-48 thread. I couldn't even confirm this as my thread pitch gauge only goes up to 40! Or is it down to 40... Oh well, a little blind faith never hurts I guess.
Here's the blank, turned down from 1/4" steel to about 0.111".
Threading tool had to be smallened quite a bit. I tried to keep the 60 degree point as close as I dare to the left side. The threads are so small that I probably could have gone even closer to the left.
I elected to not make a thread run out groove because I thought it would make the part even more fragile than it already is.
After just a few passes at a very slow speed...
Tiny threads!
Originally I had planned to turn down the other end to a long narrow shaft, maybe 0.125 by 1.000", then heat/bend it into a dog leg shape so that the indicator would hit the carriage more squarely. Then I thought, I have some old Noga deburring tool blades. They're already a dog leg shape and hardened to boot. So I did this, bored a 0.125" hole in the opposite end...
And slid in a deburring tool blade
The finished part!
The dog leg allows the indicator to hit the carriage a little more squarely.
In this pic it looks like there's a slight misalignment between the indicator shaft and my part. Could the end of the indicator shaft not be square? This is a cheap Harbor Freight indicator.
Another view. Still looks to be very slightly not straight.
As far as keeping the deburring blade in the tip, I was considering just using a drop or two of Loctite. Alternatively I think I can drill/tap a cross hole for a 6-32 set screw. Any thoughts on that?