"Paul K. Dickman" wrote in message
...

"Ed Huntress" wrote in message
...

"Robert Swinney" wrote in message
...
That worry kinda goes away if you grind an accurate Acme profile and
feed straight in, slowly.

Bob Swinney
"Ed Huntress" wrote in message
...

"BillMe" 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?
Friends have not heard of an acme tap. Thought someone might know.

Thanks,

Bill A

There are such taps. I have one, 1/2" x 10 Acme.

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.

--
Ed Huntress

I've never seen an explanation of what you do that, Bob. Why plunge
straight in, nearly doubling the chip load, rather than feeding in on an
angle and cutting on one flank, as with conventional threads?

There must be some simple reason that I've just never come across.

--
Ed Huntress


The fallacy in the argument is the assumption that feeding straight in
would double the chip load. This is true with vee threads because you are
in fact cutting twice as many sides.

I am too lazy to do the trig, but I drew the acme thread on a cad program
and found that the difference in chip load between the two methods is
pretty small.

Feeding at 14.5 deg for each unit of depth of cut at the root of the
thread, I get .499 units on one flank and 0 units on the other.
1+.499+0=1.499

Feeding straight in, I get .252 units on each flank
1+.252+.252=1.504

Paul K. Dickman

I don't do math on Sundays g, but are you measuring "chip load" in terms
of metal volume being removed? That's the common definition of the term, and
I shouldn't have used it. What I meant was cutting force, rather than chip
load.

I'm rusty on that but the primary factor determining cutting force in
turning, IIRC, is the depth of cut, with the feedrate being a relatively
minor issue. The depth of cut, or the effective equivalent in terms of
cutting force, in the case of a turning insert plunged straight in, is twice
the actual depth, multiplied by the secant of the flank angle. Add the
length of the flat at the tip of the cutter, if you want to get it all.

Right? I'll try it again on Monday. d8-)

--
Ed Huntress