In article ,
Vincent Coppola wrote:
Hello,

I am rehousing a webcam for use in astronomy and I turned down on my
minilathe a simple adapter tube out of aluminum to fit the standard
1.25" diam eyepiece holder.
I now have to turn an inside thread to hold
a standard filter. The filter requires a 1.125" x 40tpi thread. I am
trying to grind my own highspeed steel tool and having some difficulty
getting the threads to look right. They are there but look flattened.

Hmm ... at a first guess, you don't have enough relief below the
point. Remember that your workpiece is curving towards the tool, so you
need to grind away enough (a curve) below the point so it stays clear of
the workpiece. The smaller the ID, the more the curve needed to clear.

Personally, I would use laydown insert tooling for this. I find
tooling for that made in Israel (ISCAR is the brand, IIRC) for very
small inside threads. I think almost small enough to handle
single-pointing a 1/4-20 thread, and at least small enough for a 5/16"
thread.

Does someone have a dimension or procedure for grinding such a
tool to work with aluminum? Would the same tool work for delrin? I

What lube are you using for aluminum? The easiest to use is a
spray can of WD-40 -- it makes a nice aluminum cutting lube.

For the Delrin, you should not need any lube (or coolant) unless
you are turning *way* too fast.

have searched the web many times and I can turn up very little on this
subject.

Please advise,

You have my thoughts above.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---