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Bob La Londe[_7_]

On 8/25/2018 11:10 AM, wrote:
I have had to relieve the diameter of tap shanks many times in order
to tap deep holes or to cross a bore and the like. This morning I
needed to reduce the shank of a 5/16-18 tap. The job required that all
but about 3/8" of the shank diameter needed to be turned down. This
meant that in order to do the turning in one chucking the end of the
tap needed to be supported. The tap in question was a spiral point
tap. So I used a live center for support. I put a .25 thick piece of
aluminum between the point of the center and the tap. Then, with the
spindle turning, I cranked the tailstock quill forward until the
center and the tap points had both made pretty deep depressions in the
aluminum piece. I used a coated threading insert to turn down the tap.
255 RPM and .004" feed. The material was removed in one pass. I
plunged the tool into the work where the cut would not be an
interrupted cut. Then fed away from the chuck by hand to remove the
incomplete threads. This part of the cutting was an interrupted cut so
I wanted to feel the cutting. After removing the incomplete threads
the cut was reversed so that the tool was feeding towards the chuck.
The operation worked quite well and the threading insert still looks
good. HSS taps are hard but coated carbide is much harder.
Eric

I had to turn down the shank on a reamer not to long ago, and wrote
about it here I think. Used a bright shiny solid carbide TNMG insert.
The cut screamed, but the finished looked really good. I thought about
using a similar coated insert, but I didn't have one at the time. A
coated one might not have been "quite" as sharp though so who knows how
it would work out. Now, thanks to your post... I might try a coated one
next time around.

Nice to have some metal working content. Thank you.