On 2010-06-25, Tim Wescott wrote:
On 06/25/2010 08:12 AM, Robert Swinney wrote:
(top posting fixed)
Bob Swinney
"Ed wrote in message ...

wrote in message
...
I need to cut an acme thread in a steel block. Roughly 5/8" X 6. I
forget what I measured! Is that done with a tap or a boring bar?

[ ... ]

Boring a female Acme thread is something I've never tried. I still scratch
my head over single-point turning of *external* Acme threads. Some of the
old books tell you to cut both flanks at once, but I've never figured out
why. I made a couple of Acme threaded shafts in 1/2" x 10, and cutting on
one flank, just scraping the other, seemed to work Ok.

That worry kinda goes away if you grind an accurate Acme profile
and feed straight in, slowly.

Doesn't that mean then that you need a different threading bit for each
diameter and pitch of Acme thread you'll ever do? Or do you just need a
different bit for each pitch, with enough clearance for the smaller
diameters?

I fed in at an angle of 14 degrees (a little less than the
half-way point). But I ground a bit specifically for the thread I was
cutting, including side clearance angles calculated for 5 degree
clearance with the pitch and diameter I was working with for maximum
strength. A more general tip (more clearance to adopt to various
diameters and thus different thread angles) would have to be weaker.

And yes -- you make (or buy) a separate tool for each pitch you
cut. My 12x24" Clausing can handle insert tools for above 10 TPI, but
not up to the big bronze nut I was making -- so I had to make my own
tool bit from HSS there.

Enjoy,
DoN.

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