[Ignoramus16954]

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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[David Billington]

Ignoramus16954 wrote:
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?


Unless your lathe has absolutely no backlash anywhere then you are going
to need to withdraw the tool prior to reversing as it will take a
different path in the reverse direction and probably ruin your piece. It
is how I cut many threads especially metric as although the Harrison
M300 has a universal thread cutting gearbox the leadscrew is inch.

[Paul K. Dickman]

If you are talking about using the tumbler reverse in the gear train, the
answer is, "no". It disengages the gears and looses position.

If you are talking about reversing the motor, the answer is' "yes it is
possible"
You still have to back the cutter out of the cut, however. Reversing the
motor swings all the backlash in the system the other way and the tool will
drag over the threads.

Paul K. Dickman

"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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inattention
to spammers, I and many others block all articles originating
from Google Groups. If you want your postings to be seen by
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[Pete Snell]

Ignoramus16954 wrote:
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?


Sort of right. You will need to withdraw the cutter to reverse, but
that just means backing it out a set amount with the cross-slide and
then setting it back when making the cut. Usually you would only use
this method when cutting an odd thread, such as a metric thread on a
machine with a standard leadscrew. Normally the threading dial would be
used as a reference to restart the thread on each return. It's pretty
tedious to reverse the lathe at the end of each pass, and then switch to
forward. Much quicker to use the handwheel on the carriage to return for
each pass.

Pete

--
Pete Snell
Department of Physics
Royal Military College
Kingston, Ontario,
Canada
-----------------------------------------------------------------------
All truths are easy to understand once they are discovered;
the point is to discover them.

Galileo Galilei (1564-1642)

[David Harmon]

On Thu, 10 Jul 2008 09:44:56 -0500 in rec.crafts.metalworking,
Ignoramus16954 wrote,
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?

Yes, you can do that. If your lathe has no half-nuts, like my Emco
Compact 5, you pretty much have to do it that way.

[Ignoramus16954]

On 2008-07-10, Paul K. Dickman wrote:
If you are talking about using the tumbler reverse in the gear train, the
answer is, "no". It disengages the gears and looses position.

If you are talking about reversing the motor, the answer is' "yes it is
possible"

I am talking about reversing the motor, if I only reversed the
carriage, it would try to cut the opposite thread (left handed).

You still have to back the cutter out of the cut, however. Reversing the
motor swings all the backlash in the system the other way and the tool will
drag over the threads.

I see. The backlash would screw up the thread. However, keeping the
carriage engaged at all times, would keep it along the thread when
running in the right-to-left direction.

i


Paul K. Dickman

"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?




--
Due to extreme spam originating from Google Groups, and their inattention
to spammers, I and many others block all articles originating
from Google Groups. If you want your postings to be seen by
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posting on Usenet.
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[Jim Wilkins]

I do threading like a state machine. Each starred state is
uninterruptible and leaves the machine in a distinct condition, so i
know where I am after measuring or answering the phone. The cross
slide and compound dials are set to zero when the tip barely scratches
the work.

*At the end of the cut disengage the half nuts and back out the slide
exactly 0.100, ie to the next 0 at this point.

*Move the carriage back past the end of the work. Turn the slide in
one turn.

*Advance the compound a few thousandths. Engage the half nuts when the
proper line on the threading dial matches, or move the carriage to
meet it.

The last few fine cuts to adjust the fit are done straight in with the
slide, to smooth both thread flanks. Turning the dial exactly one turn
preserves its setting if I'm interrupted.

I added the threading dial line and the 29 degree infeed depth to the
quick-change gearbox chart.

Jim Wilkins

[Dave August]

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.

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?

--
Due to extreme spam originating from Google Groups, and their
inattention
to spammers, I and many others block all articles originating
from Google Groups. If you want your postings to be seen by
more readers you will need to find a different means of
posting on Usenet.
http://improve-usenet.org/

[Robert Swinney]

Good advice David, Iggy's probably has no nuts.

Bob Swinney
"David Harmon" wrote in message
m...
On Thu, 10 Jul 2008 09:44:56 -0500 in rec.crafts.metalworking,
Ignoramus16954 wrote,
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?

Yes, you can do that. If your lathe has no half-nuts, like my Emco
Compact 5, you pretty much have to do it that way.

** Posted from http://www.teranews.com **

[David Billington]

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?

--
Due to extreme spam originating from Google Groups, and their
inattention
to spammers, I and many others block all articles originating
from Google Groups. If you want your postings to be seen by
more readers you will need to find a different means of
posting on Usenet.
http://improve-usenet.org/

[DoN. Nichols]

On 2008-07-10, Ignoramus16954 wrote:
I am trying to recall some 20 year old high school memories.

Were those high school memories here int eh US, or in Russia?
If the latter, then you were probably cutting metric threads, and the
machine may have been different enough to add to the confusion.

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?

Wrong -- because there is backlash in the leadscrew/half-nuts
connection, so it does not return along the same path that it took when
cutting.

And stop/reverse requires a very fast reverse if you are cutting
towards a shoulder.

Better to cut a runout groove to the depth of the thread, and
wide enough to allow for your reaction time with the half nuts, use that
to disengage the half nuts, crank the cross-slide back far enough to be
*sure* to clear the threads, and hand crank back to off the start end of
the thread, then wait for the threading dial to reach the right point
(what is the right point depends on the thread pitch being cut -- for
some pitches, any mark on the dial will do. For others, every numbered
mark. For others every *even* numbered mark, and for yet others only
the same mark as was used the first pass. (Where you are doing every
even mark -- if you start on an odd mark, it can be every odd mark
instead.) Check the manual for the lathe -- it will tell you which
selection of marks to use for a given thread. Basically, if the pitch
can be evenly divided by four you can use any mark on my lathe, but
yours may be different.

Oh yes -- also start with the cross slide set to 0 on the dial
and the cutting tool touching the workpiece, and with the compound set
to zero as well, and with an angle of 29.5 degrees for US/Metric
threads. Then for each cut -- you stop in the runout groove (using the
half nuts), leave the spindle running forwards, withdraw the cross slide
by one full turn (or two or more if necessary for a deep coarse thread),
crank back to the starting point, crank the cross-slide back in the same
number of turns, stopping on zero, and then advance the compound-slide
to set the depth of cut of the next pass, and re-engage the half-nuts
when the threading dial reaches the right point. There are stops made
for the cross-slide which allow you to simply crank back in until you
hit the stop each time which can save you a bit of time and fiddly work,
but you still feed the depth of cut using the compound -- at least for
US practice.

Enjoy,
DoN.

--
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 ---

[[email protected]]

On Jul 10, 8:38*pm, "DoN. Nichols" wrote:

...


* * * * Better to cut a runout groove to the depth of the thread, and
wide enough to allow for your reaction time with the half nuts, use that
to disengage the half nuts,

In such situations I sometimes turn the cutter upside down and run
the lathe in reverse. Usually when there's not much left on the
left. :-)

DOC

[clare at snyder dot ontario dot canada]

On Thu, 10 Jul 2008 09:44:56 -0500, Ignoramus16954
wrote:

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 guess you COULD - but that's NOT the right way to do it. You will be
wubbing the cutter backwards in the thread as you reverse the lathe.
The thread dial is your FRIEND. Figure out how to use it.

I do not need to withdraw the cutter, move it back, find the proper
spot to restart, etc. Right or wrong?

** Posted from http://www.teranews.com **

[Jim Wilkins]

On Jul 10, 3:38*pm, "Dave August" wrote:
...
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.
.....
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

Interesting. When there isn't room for an end groove I stop the lathe
short and pull the belt to finish the pass, then chisel and file out
the stack of chips at the end of the thread afterwards. Maybe the tip
never has broken because the cut is only 2-3 thousandths, or the old
South Bend 10L is -so- springy it doesn't have enough force to break
the tip. I keep the belt loose enough that the cutoff bit can jam
without breaking.

Jim Wilkins

[Stealth Pilot]

On Thu, 10 Jul 2008 09:49:48 -0700 (PDT), Jim Wilkins
wrote:

I do threading like a state machine. Each starred state is
uninterruptible and leaves the machine in a distinct condition, so i
know where I am after measuring or answering the phone. The cross
slide and compound dials are set to zero when the tip barely scratches
the work.

*At the end of the cut disengage the half nuts and back out the slide
exactly 0.100, ie to the next 0 at this point.

*Move the carriage back past the end of the work. Turn the slide in
one turn.

*Advance the compound a few thousandths. Engage the half nuts when the
proper line on the threading dial matches, or move the carriage to
meet it.

The last few fine cuts to adjust the fit are done straight in with the
slide, to smooth both thread flanks. Turning the dial exactly one turn
preserves its setting if I'm interrupted.

I added the threading dial line and the 29 degree infeed depth to the
quick-change gearbox chart.

Jim Wilkins

thats the way to do it.
reversing the motor is awfully slow. on mine if I flip the switch into
reverse it just keeps running in the same direction.
If I stop it, then flip the switch I get reverse.
the stopping takes a while.

Stealth Pilot

[Ignoramus16038]

On 2008-07-11, DoN. Nichols wrote:
On 2008-07-10, Ignoramus16954 wrote:
I am trying to recall some 20 year old high school memories.

Were those high school memories here int eh US, or in Russia?
If the latter, then you were probably cutting metric threads, and the
machine may have been different enough to add to the confusion.

Russia.

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?

Wrong -- because there is backlash in the leadscrew/half-nuts
connection, so it does not return along the same path that it took when
cutting.

And stop/reverse requires a very fast reverse if you are cutting
towards a shoulder.

Better to cut a runout groove to the depth of the thread, and
wide enough to allow for your reaction time with the half nuts, use that
to disengage the half nuts, crank the cross-slide back far enough to be
*sure* to clear the threads, and hand crank back to off the start end of
the thread, then wait for the threading dial to reach the right point
(what is the right point depends on the thread pitch being cut -- for
some pitches, any mark on the dial will do. For others, every numbered
mark. For others every *even* numbered mark, and for yet others only
the same mark as was used the first pass. (Where you are doing every
even mark -- if you start on an odd mark, it can be every odd mark
instead.) Check the manual for the lathe -- it will tell you which
selection of marks to use for a given thread. Basically, if the pitch
can be evenly divided by four you can use any mark on my lathe, but
yours may be different.

Oh yes -- also start with the cross slide set to 0 on the dial
and the cutting tool touching the workpiece, and with the compound set
to zero as well, and with an angle of 29.5 degrees for US/Metric
threads. Then for each cut -- you stop in the runout groove (using the
half nuts), leave the spindle running forwards, withdraw the cross slide
by one full turn (or two or more if necessary for a deep coarse thread),
crank back to the starting point, crank the cross-slide back in the same
number of turns, stopping on zero, and then advance the compound-slide
to set the depth of cut of the next pass, and re-engage the half-nuts
when the threading dial reaches the right point. There are stops made
for the cross-slide which allow you to simply crank back in until you
hit the stop each time which can save you a bit of time and fiddly work,
but you still feed the depth of cut using the compound -- at least for
US practice.

Enjoy,
DoN.


Exciting. Thanks to all. In the best scenario I can actually try all
this quite soon.

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Due to extreme spam originating from Google Groups, and their inattention
to spammers, I and many others block all articles originating
from Google Groups. If you want your postings to be seen by
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[Ignoramus16038]

On 2008-07-11, Stealth Pilot wrote:
On Thu, 10 Jul 2008 09:49:48 -0700 (PDT), Jim Wilkins
wrote:

I do threading like a state machine. Each starred state is
uninterruptible and leaves the machine in a distinct condition, so i
know where I am after measuring or answering the phone. The cross
slide and compound dials are set to zero when the tip barely scratches
the work.

*At the end of the cut disengage the half nuts and back out the slide
exactly 0.100, ie to the next 0 at this point.

*Move the carriage back past the end of the work. Turn the slide in
one turn.

*Advance the compound a few thousandths. Engage the half nuts when the
proper line on the threading dial matches, or move the carriage to
meet it.

The last few fine cuts to adjust the fit are done straight in with the
slide, to smooth both thread flanks. Turning the dial exactly one turn
preserves its setting if I'm interrupted.

I added the threading dial line and the 29 degree infeed depth to the
quick-change gearbox chart.

Jim Wilkins

thats the way to do it.
reversing the motor is awfully slow. on mine if I flip the switch into
reverse it just keeps running in the same direction.
If I stop it, then flip the switch I get reverse.
the stopping takes a while.

Stealth Pilot

you must have a single phase motor
--
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from Google Groups. If you want your postings to be seen by
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[John Husvar]

In article ,
Stealth Pilot wrote:


thats the way to do it.
reversing the motor is awfully slow. on mine if I flip the switch into
reverse it just keeps running in the same direction.
If I stop it, then flip the switch I get reverse.
the stopping takes a while.

Stealth Pilot

Now from someone nearly totally clueless about threading:

How does one cut a left-hand thread?

I've somehow got the idea that if you cut from right to left, you get a
right-hand thread.

If you cut from left to right with the machine turning the same
direction, do you get a left-hand thread?

The only experience I have with a lathe is turning to a diameter. My kid
knows more than I. He made nice signaling cannon during a summer work
experience program, tapered barrel and all, but has forgotten threading
procedures since it was 20 years ago.

[Dave August]

You are "essentially" correct about cutting left to right to get a left
handed thread, but what you forgot to say is with the spindle turning in the
"normal" clockwise direction.

What you need to do is reverse the direction the lead screw turns in
relationship to the spindle what ever direction it's turning. Most good
lathes have what's called a "tumbler" that set's the direction of the lead
screw relative to the spindle.

Now you get to decide which way you want the carriage to move when you cut
the thread.

If you want to the carriage move TOWARDS the headstock, you have to run the
spindle counterclockwise and put your cutting tool upside down on the back
side.. most people don't like this since the cutting force is now LIFTING
the carriage not pressing it down... but for shallow cuts this will work..

If you run the spindle it's "normal" direction and the carriage moves away
from the head stock, you'll have to cut the equivelent of the "run out"
groove but use that as a "starting" groove.

FYI one of the issues with the 9x20 I'm selling (and other cheap imports) is
that they have no tumbler so you can only cut right hand threads.

--.- Dave


"John Husvar" wrote in message
...
In article ,
Stealth Pilot wrote:


thats the way to do it.
reversing the motor is awfully slow. on mine if I flip the switch into
reverse it just keeps running in the same direction.
If I stop it, then flip the switch I get reverse.
the stopping takes a while.

Stealth Pilot

Now from someone nearly totally clueless about threading:

How does one cut a left-hand thread?

I've somehow got the idea that if you cut from right to left, you get a
right-hand thread.

If you cut from left to right with the machine turning the same
direction, do you get a left-hand thread?

The only experience I have with a lathe is turning to a diameter. My kid
knows more than I. He made nice signaling cannon during a summer work
experience program, tapered barrel and all, but has forgotten threading
procedures since it was 20 years ago.

[DoN. Nichols]

On 2008-07-11, Jim Wilkins wrote:

[ ... ]

Interesting. When there isn't room for an end groove I stop the lathe
short and pull the belt to finish the pass, then chisel and file out
the stack of chips at the end of the thread afterwards.

It avoid the stack of chips, you can try doing it the way old
machinists used to do it. This calls for threading mounted between
centers so you can remove it and replace it to continue. Make a scratch
cut only, remove the workpiece and take it to the drill press or mill
and drill a hole right where you want the thread to stop and just deep
enough to receive the cutter, then you can hand feed it to the hole and
the chips break off cleanly. I've never yet done this, but I probably
will try it sometime.

Enjoy,
DoN.

--
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 ---

[DoN. Nichols]

On 2008-07-11, Stealth Pilot wrote:
On Thu, 10 Jul 2008 09:49:48 -0700 (PDT), Jim Wilkins
wrote:

[ ... ]

*At the end of the cut disengage the half nuts and back out the slide
exactly 0.100, ie to the next 0 at this point.

*Move the carriage back past the end of the work. Turn the slide in
one turn.

*Advance the compound a few thousandths. Engage the half nuts when the
proper line on the threading dial matches, or move the carriage to
meet it.

[ ... ]

thats the way to do it.
reversing the motor is awfully slow. on mine if I flip the switch into
reverse it just keeps running in the same direction.
If I stop it, then flip the switch I get reverse.
the stopping takes a while.

So you have a single phase motor. This is one of the places
where three phase wins -- you can "plug" reverse -- just switch into
reverse at the proper time (and quickly crank the cross-feed out during
the moment in which the spindle is stalled). Or -- if you have three
phase and a VFD, you can tune the ramp-down and ramp-up times to more
reasonably match the available power, and have a little more time to
crank out the cross slide -- if you *have* to run it in reverse instead
of disengaging the half nuts and cranking the carriage back. (You do
wind up in this situation when you're doing metric threads on an
imperial lathe, or vice versa.)

Enjoy,
DoN.

--
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 ---

[DoN. Nichols]

On 2008-07-11, John Husvar wrote:

[ ... ]

Now from someone nearly totally clueless about threading:

How does one cut a left-hand thread?

I've somehow got the idea that if you cut from right to left, you get a
right-hand thread.

If you cut from left to right with the machine turning the same
direction, do you get a left-hand thread?

Yes. Ideally you want to move the compound from the position of
29.5 degrees crank towards tailstock to the same angle towards headstock
instead so you can follow the flank of the trailing edge of the cut,
only making a very shallow cut there for each pass while making a deeper
cut on the leading edge.

And you don't do the full depth in a single pass -- unless it is
a very fine and shallow thread -- say something like 80 TPI or finer.

And also -- aside from setting the gearbox (or changing the
gears, depending on the lathe involved), you also want to use the
half-nuts to engage carriage motion -- not the power feed which works
through the handwheel. (Of course, some lathes don't have the power
feed, only the half nuts, so the question becomes moot.)

The only experience I have with a lathe is turning to a diameter. My kid
knows more than I. He made nice signaling cannon during a summer work
experience program, tapered barrel and all, but has forgotten threading
procedures since it was 20 years ago.

The main thing for the first threads is to make sure that you've
got plenty of space for reaction time to stop the cut -- don't make your
first threads cut to a shoulder. :-)

Easiest is if you have a reduced diameter both before and after
the area to be threaded. If you don't have that, cut a runout groove to
the depth of the thread at the end of your thread. The needed width
will vary with the coarseness of the thread, the speed of the spindle,
and your reaction time. Before you actually cut the thread, back the
tool out far enough so it will clear the increased diameter of the
workpiece at the end of the thread, and try some practice runs -- using
the dial to determine when to engage the half nuts, and seeing how
consistent you can be as to where you disengage the half nuts. That
will give you an idea how wide the runout groove needs to be for this
thread. Coarser threads move the carriage faster and require faster
reaction times. Really fine threads give you a lot more leeway in
reaction time.

Enjoy,
DoN.

--
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--- Black Holes are where God is dividing by zero ---

[DoN. Nichols]

On 2008-07-11, Dave August wrote:
You are "essentially" correct about cutting left to right to get a left
handed thread, but what you forgot to say is with the spindle turning in the
"normal" clockwise direction.

He *did* say "with the machine turning in the same direction".
Here is the quoted text which you left below and which I have moved up
here to make it clear what refers to what.

If you cut from left to right with the machine turning the same
direction, do you get a left-hand thread?

Enjoy,
DoN.

--
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 ---

[Jim Wilkins]

On Jul 11, 10:54*pm, "DoN. Nichols" wrote:
On 2008-07-11, Jim Wilkins wrote:

* * * * It avoid the stack of chips, you can try doing it the way old
machinists used to do it. *This calls for threading mounted between
centers so you can remove it and replace it to continue. *Make a scratch
cut only, remove the workpiece and take it to the drill press or mill
and drill a hole right where you want the thread to stop and just deep
enough to receive the cutter, then you can hand feed it to the hole and
the chips break off cleanly. *I've never yet done this, but I probably
will try it sometime.

* * * * Enjoy,
* * * * * * * * DoN.

I did that once or twice by drilling at the end of the thread scratch
with a hand drill, since the stock was in a collet.

The point was that my belt-driven lathe doesn't seem to break bits
when stopped during a cut. Could it happen only on geared lathes?

[Stealth Pilot]

On 12 Jul 2008 03:18:33 GMT, "DoN. Nichols"
wrote:

On 2008-07-11, Dave August wrote:
You are "essentially" correct about cutting left to right to get a left
handed thread, but what you forgot to say is with the spindle turning in the
"normal" clockwise direction.

He *did* say "with the machine turning in the same direction".
Here is the quoted text which you left below and which I have moved up
here to make it clear what refers to what.

If you cut from left to right with the machine turning the same
direction, do you get a left-hand thread?

Enjoy,
DoN.

there is one other gotcha.
you need to position the tool so that the body of the tool below the
cutting edge is aligned to the helix angle of the thread that you are
cutting. ...otherwise the (what do you call it??? the base, the foot
of the tool???) bit of the tool below the cutting edge will tear the
thread as it graunches past it.
this is easily achieved by tilting the tool.

the gotcha is that for threads in different directions the tilt is
reversed. the tool is set up the opposite way to a right hand thread
for left hand threads.

Stealth Pilot

[Stealth Pilot]

On 12 Jul 2008 03:00:03 GMT, "DoN. Nichols"
wrote:

On 2008-07-11, Stealth Pilot wrote:
On Thu, 10 Jul 2008 09:49:48 -0700 (PDT), Jim Wilkins
wrote:

[ ... ]

*At the end of the cut disengage the half nuts and back out the slide
exactly 0.100, ie to the next 0 at this point.

*Move the carriage back past the end of the work. Turn the slide in
one turn.

*Advance the compound a few thousandths. Engage the half nuts when the
proper line on the threading dial matches, or move the carriage to
meet it.

[ ... ]

thats the way to do it.
reversing the motor is awfully slow. on mine if I flip the switch into
reverse it just keeps running in the same direction.
If I stop it, then flip the switch I get reverse.
the stopping takes a while.

So you have a single phase motor. This is one of the places
where three phase wins -- you can "plug" reverse -- just switch into
reverse at the proper time (and quickly crank the cross-feed out during
the moment in which the spindle is stalled). Or -- if you have three
phase and a VFD, you can tune the ramp-down and ramp-up times to more
reasonably match the available power, and have a little more time to
crank out the cross slide -- if you *have* to run it in reverse instead
of disengaging the half nuts and cranking the carriage back. (You do
wind up in this situation when you're doing metric threads on an
imperial lathe, or vice versa.)

Enjoy,
DoN.

yep, yep, yep

(i'm not a yes man :-) )
Stealth Pilot