K. H. Moltrecht in his book Machine Shop Practice advises: " . . . The
left-hand side-cutting tool should have a 10- to 17-degree relief angle on
the flank below the right side-cutting edge, and an 8- to 12-degree relief
angle below the left-hand cutting edge. . . . ".

Can someone please explain why the 2 respective relief angles should not be
the same ?

Bob Swinney

On Sat, 26 May 2012 09:58:16 -0500, wrote:

K. H. Moltrecht in his book Machine Shop Practice advises: " . . . The
left-hand side-cutting tool should have a 10- to 17-degree relief angle on
the flank below the right side-cutting edge, and an 8- to 12-degree relief
angle below the left-hand cutting edge. . . . ".

Can someone please explain why the 2 respective relief angles should not be
the same ?

Bob Swinney

What the heck is a "left-hand cutting edge" on a left-hand
side-cutting tool?

--
Ed Huntress

wrote:
K. H. Moltrecht in his book Machine Shop Practice advises: " . . .
The left-hand side-cutting tool should have a 10- to 17-degree relief
angle on the flank below the right side-cutting edge, and an 8- to
12-degree relief angle below the left-hand cutting edge. . . . ".

Can someone please explain why the 2 respective relief angles should
not be the same ?

Bob Swinney
To take into account the helix angle of the thread.

On Sat, 26 May 2012 16:10:29 +0100, David Billington
wrote:

wrote:
K. H. Moltrecht in his book Machine Shop Practice advises: " . . .
The left-hand side-cutting tool should have a 10- to 17-degree relief
angle on the flank below the right side-cutting edge, and an 8- to
12-degree relief angle below the left-hand cutting edge. . . . ".

Can someone please explain why the 2 respective relief angles should
not be the same ?

Bob Swinney
To take into account the helix angle of the thread.

And how do you thread with a side-cutting tool?

--
Ed Huntress

"Ed Huntress" wrote in message
...
On Sat, 26 May 2012 16:10:29 +0100, David Billington
wrote:

wrote:
K. H. Moltrecht in his book Machine Shop Practice advises: " . . .
The left-hand side-cutting tool should have a 10- to 17-degree relief
angle on the flank below the right side-cutting edge, and an 8- to
12-degree relief angle below the left-hand cutting edge. . . . ".

Can someone please explain why the 2 respective relief angles should
not be the same ?

Bob Swinney
To take into account the helix angle of the thread.

And how do you thread with a side-cutting tool?


By setting the compound at 30 degrees.

On Sat, 26 May 2012 08:39:02 -0700, "PrecisionmachinisT"
wrote:


"Ed Huntress" wrote in message
.. .
On Sat, 26 May 2012 16:10:29 +0100, David Billington
wrote:

wrote:
K. H. Moltrecht in his book Machine Shop Practice advises: " . . .
The left-hand side-cutting tool should have a 10- to 17-degree relief
angle on the flank below the right side-cutting edge, and an 8- to
12-degree relief angle below the left-hand cutting edge. . . . ".

Can someone please explain why the 2 respective relief angles should
not be the same ?

Bob Swinney
To take into account the helix angle of the thread.

And how do you thread with a side-cutting tool?


By setting the compound at 30 degrees.

My point is that a side-cutting tool has had a specific meaning for
over 100 years. It will not thread. The end relief will not allow it.
A left-hand *facing* tool might allow it, but the point would likely
be too rounded, and the side relief on the left side of the tool is
not likely to be 60 degrees to the cutting edge.

What I was getting at is that there is a terminology problem here, and
it's confusing. What the book probably was talking about is a
left-hand threading tool, not a left-hand side-cutting tool.

--
Ed Huntress

On Sat, 26 May 2012 09:58:16 -0500, wrote:

K. H. Moltrecht in his book Machine Shop Practice advises: " . . . The
left-hand side-cutting tool should have a 10- to 17-degree relief angle on
the flank below the right side-cutting edge, and an 8- to 12-degree relief
angle below the left-hand cutting edge. . . . ".

Can someone please explain why the 2 respective relief angles should not be
the same ?

Bob Swinney

FWIW, my hand ground HSS thread cutting tool has a bit more than ten
dgree relief on both sides. I've used it for both left and right hand
threads.

Your text is getting at allowing for the slant of the theads. I could
see this being a problem on huge diameter threading.

Karl, still waiting on your apple pick up visit.

wrote in message
...
K. H. Moltrecht in his book Machine Shop Practice advises: " . . .
The left-hand side-cutting tool should have a 10- to 17-degree
relief angle on the flank below the right side-cutting edge, and an
8- to 12-degree relief angle below the left-hand cutting edge. . . .
".

Can someone please explain why the 2 respective relief angles should
not be the same ?

Bob Swinney

You don't need to obsess about proper angles in a home shop where the
tools do relatively little cutting, aren't left unattended and can be
reground whenever you want without messing up a long repetitive job.

An HSS lathe bit cutting edge wears by developing a flat below the
edge. Once that flat grows to ~1/32" or so high it skates over the
work, according to some old books from Lindsay. Look at a dulled edge
with a magnifier.

If the angle is too shallow, or vertical, only a little metal has to
rub off to grow the flat. If it's too acute the tool can dig in or the
edge can chip. The condition of your lathe affects how likely that is.
Mine's bad so I keep the front relief angle moderate and sharpen more
often.

You soon learn what cuts easily and lasts long enough by
experimenting. The top can be left horizontal to avoid chasing two
interacting variables.

When you regrind a threading bit part way through the job you can
bevel the starting end with hand feed to confirm that it will still
cut.

jsw

On 2012-05-26, wrote:
K. H. Moltrecht in his book Machine Shop Practice advises: " . . . The
left-hand side-cutting tool should have a 10- to 17-degree relief angle on
the flank below the right side-cutting edge, and an 8- to 12-degree relief
angle below the left-hand cutting edge. . . . ".

Can someone please explain why the 2 respective relief angles should not be
the same ?

Because they are cutting a groove which is slanted relative to a
vertical. And which way they are slanted is based on whether the
threads are right-hand or left hand. Right hand threading tools are
about the same, except that the angles swap sides.

What *I* do is calculate the basic angle by calculating from the
pitch and the circumference. Then I add what feels right (I've used
just 5 degrees to the angle on one side and subtract it on the other
side to produce consistent clearance. This results in a tool which is
just right for a specific pitch and diameter, and *might* work well for
another combination of pitch and diameter, as long as they calculate to
the same angle. The values given in Moltrecht's book are more general
purpose values -- should work with most things, except perhaps if you
are cutting a triple lead thread or something similarly strange which
results in an extreme thread angle.

The time I did this, I was cutting a replacement nut for a log
splitter. Acme, and pretty aggressive cut, so I minimized the clearance
in favor of strength.

Good Luck,
DoN.

--
Remove oil spill source from e-mail
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 ---

"Ed Huntress" wrote in message
...
On Sat, 26 May 2012 08:39:02 -0700, "PrecisionmachinisT"
wrote:


"Ed Huntress" wrote in message
. ..
On Sat, 26 May 2012 16:10:29 +0100, David Billington
wrote:

wrote:
K. H. Moltrecht in his book Machine Shop Practice advises: " . . .
The left-hand side-cutting tool should have a 10- to 17-degree relief
angle on the flank below the right side-cutting edge, and an 8- to
12-degree relief angle below the left-hand cutting edge. . . . ".

Can someone please explain why the 2 respective relief angles should
not be the same ?

Bob Swinney
To take into account the helix angle of the thread.

And how do you thread with a side-cutting tool?


By setting the compound at 30 degrees.

My point is that a side-cutting tool has had a specific meaning for
over 100 years. It will not thread. The end relief will not allow it.
A left-hand *facing* tool might allow it, but the point would likely
be too rounded, and the side relief on the left side of the tool is
not likely to be 60 degrees to the cutting edge.

What I was getting at is that there is a terminology problem here, and
it's confusing. What the book probably was talking about is a
left-hand threading tool, not a left-hand side-cutting tool.


Im not confused at all by it.

The side of a threading tool that is properly designed for use in a
threading process where the depth of cut for each sucessive pass is
controlled by dialing the compound feed inward at an angle equalk to 1/2 of
the vee thread angle, is the only portion of the tool that is ever going to
be in contact with the workpiece, pure and simple.

Hopefully you can parse the above...

--probably it will be an excercise in itself though--my having had a couple
beers earlier certainly didn't make my writing it out any easier than it
might have been, otherwise.

"Jim Wilkins" wrote in message
...

wrote in message
...
K. H. Moltrecht in his book Machine Shop Practice advises: " . . . The
left-hand side-cutting tool should have a 10- to 17-degree relief angle
on the flank below the right side-cutting edge, and an 8- to 12-degree
relief angle below the left-hand cutting edge. . . . ".

Can someone please explain why the 2 respective relief angles should not
be the same ?

Bob Swinney

You don't need to obsess about proper angles in a home shop where the
tools do relatively little cutting, aren't left unattended and can be
reground whenever you want without messing up a long repetitive job.

An HSS lathe bit cutting edge wears by developing a flat below the edge.
Once that flat grows to ~1/32" or so high it skates over the work,
according to some old books from Lindsay. Look at a dulled edge with a
magnifier.


THat is probably true where you have "built-up edge"., otherwise, there
develops a radius, whereas at some point the tool won't give a clean cut
unless your infeed amount is substantially larger than the radius.


If the angle is too shallow, or vertical, only a little metal has to rub
off to grow the flat. If it's too acute the tool can dig in or the edge
can chip. The condition of your lathe affects how likely that is. Mine's
bad so I keep the front relief angle moderate and sharpen more often.

You soon learn what cuts easily and lasts long enough by experimenting.
The top can be left horizontal to avoid chasing two interacting variables.

When you regrind a threading bit part way through the job you can bevel
the starting end with hand feed to confirm that it will still cut.

jsw

On Sat, 26 May 2012 21:55:47 -0700, "PrecisionmachinisT"
wrote:


"Ed Huntress" wrote in message
.. .
On Sat, 26 May 2012 08:39:02 -0700, "PrecisionmachinisT"
wrote:


"Ed Huntress" wrote in message
...
On Sat, 26 May 2012 16:10:29 +0100, David Billington
wrote:

wrote:
K. H. Moltrecht in his book Machine Shop Practice advises: " . . .
The left-hand side-cutting tool should have a 10- to 17-degree relief
angle on the flank below the right side-cutting edge, and an 8- to
12-degree relief angle below the left-hand cutting edge. . . . ".

Can someone please explain why the 2 respective relief angles should
not be the same ?

Bob Swinney
To take into account the helix angle of the thread.

And how do you thread with a side-cutting tool?


By setting the compound at 30 degrees.

My point is that a side-cutting tool has had a specific meaning for
over 100 years. It will not thread. The end relief will not allow it.
A left-hand *facing* tool might allow it, but the point would likely
be too rounded, and the side relief on the left side of the tool is
not likely to be 60 degrees to the cutting edge.

What I was getting at is that there is a terminology problem here, and
it's confusing. What the book probably was talking about is a
left-hand threading tool, not a left-hand side-cutting tool.


Im not confused at all by it.

The side of a threading tool that is properly designed for use in a
threading process where the depth of cut for each sucessive pass is
controlled by dialing the compound feed inward at an angle equalk to 1/2 of
the vee thread angle, is the only portion of the tool that is ever going to
be in contact with the workpiece, pure and simple.

Well, the standard compound setting for threading tools used to be
29-1/2 degrees, not 30 degrees, so the "back" side of the tool would
at least skive the other side of the V, if not actually cut it. I
realize that old standard is not observed in many cases, especially
these days.

As for what the OP meant by a "side-cutting tool," again, the
terminology is sort of burned into me and a standard side-cutting tool
has a cutting angle a few degrees less than perpendicular to the
direction of the cut, with an end-relief (back from the cutting
direction) of only a few degrees from parallel to the work. There also
are side-cutters with much more front relief, called "facing tools"
back in the day.

So I was trying to figure out if he was trying to thread with a
side-cutting tool, or maybe a facing tool, and I was getting
discumbobulated.

My word mess is probably harder to follow than your two-beer word
tangle. d8-)

I guess he meant a left-hand threading tool all along, and I should
have realized that from the header.

--
Ed Huntress


Hopefully you can parse the above...

--probably it will be an excercise in itself though--my having had a couple
beers earlier certainly didn't make my writing it out any easier than it
might have been, otherwise.