Dave August wrote:
Iggy,
Besides the backlash issues everyone has raised there is another problem.
If you stop the work from turning while the tool bit is cutting, either by
turning off the motor or disengaging the clutch, you'll most likely break
the tip of the cutter. Typically you disengage the halfnut and leave the
work turning, and yes it leaves a ring at the end of your threads.
Normally when thread cutting the first thing I do is cut a run out
groove at the end of the thread to the minor diameter of the thread, or
major in the case of internal threads. I can't consistently stop at the
same place each time to avoid possibly taking a heavy cut if I stop a
little to far in towards the end of the htreading, now if I ran at the
lowest speed, 40 RPM, maybe but for what I do a small runout groove
allows me to thread faster.
FWIW I had an old time machinist prove this to me one afternoon. We were
discussing threading and he told me this and I didn't believe him so I
chucke up a piece of stock, did a quick gring on a threading bit and cut a
few threads, disengaged the cluths and.. nothing happend no problem.. the
old guy laughed and said try it again so i did, and... snap, there went the
tip of the cutter.. I re-ground it and tried again and .. snap.. same thing
broke off the end.. I did it about 10 times and 8 out of the 10 snapped the
tip off.. It was a great object lession :-)
IIRC his explanation was that the tool holder, tool and work piece DO
deflect and when you stop the work with the tool engaged the "spring back"
force drives the workpiece backwards against the tool and snaps the tip
off...
--.- Dave
"Ignoramus16954" wrote in message
...
I am trying to recall some 20 year old high school memories. If I am
cutting a thread on a lathe, and the lathe is reversible, then I can
cut the thread one way, stop/reverse the lathe, return, set the cutter
deeper, and repeat, right?
I do not need to withdraw the cutter, move it back, find the proper
spot to restart, etc. Right or wrong?
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