I am reading various sources for information on threading in the
lathe. A lot is said about external threads, but not near as much
about internal threading.

For the moment, I am interested in cutting right-hand internal v
threads.

Various sources say to turn the compound 29.5 - 30 degrees to the
left. Disadvantage: No room to enter hole. Or leave compound to the
right and turn tool upside down. Or put compound in rear right
corner. Disadvantage: Have to lean over lathe to adjust. Other
permutations of these exist when the lathe is run backwards.
Disadvantage: Danger of unscrewing the chuck.

Why can't you just leave the compound set the same way as when cutting
external threads (29.5-30 to the right) with the tool in the normal
right side up position? The tool is still only going to cut on one
side. This time it will be mostly cutting on the rear side of the
tool and not the front as when cutting external threads.

Any thoughts would be greatly appreciated. Thank You

I am reading various sources for information on threading in the
lathe. A lot is said about external threads, but not near as much
about internal threading.

For the moment, I am interested in cutting right-hand internal v
threads.

Various sources say to turn the compound 29.5 - 30 degrees to the
left. Disadvantage: No room to enter hole. Or leave compound to the
right and turn tool upside down. Or put compound in rear right
corner. Disadvantage: Have to lean over lathe to adjust. Other
permutations of these exist when the lathe is run backwards.
Disadvantage: Danger of unscrewing the chuck.

Why can't you just leave the compound set the same way as when cutting
external threads (29.5-30 to the right) with the tool in the normal
right side up position? The tool is still only going to cut on one
side. This time it will be mostly cutting on the rear side of the
tool and not the front as when cutting external threads.

Any thoughts would be greatly appreciated. Thank You



With the feed going the same way as the pressure from the cut, the tool may
tend to jump ahead a bit. Better to have the feed forcing the tool into the
cut.

The easiest way to thread is with a cross slide stop, but the only way you can
use one while internal threading is if you cut on the far side of the axis,
whether upside down or right side up.

John Martin

(JMartin957)

With the feed going the same way as the pressure from the cut, the tool may
tend to jump ahead a bit. Better to have the feed forcing the tool into the
cut.

And if you have loose gibs, loose carriage, there's even more bounce of the
tool bit out of the cut--the tool bit is forced to the center of the bore--is
what you are saying, if I read you right?

Frank Morrison

(JMartin957)

With the feed going the same way as the pressure from the cut, the tool may
tend to jump ahead a bit. Better to have the feed forcing the tool into the
cut.

And if you have loose gibs, loose carriage, there's even more bounce of the
tool bit out of the cut--the tool bit is forced to the center of the bore--is
what you are saying, if I read you right?

Frank Morrison



Not to the center of the bore, but toward the headstock. You want the cutting
force to be acting against the feed, not with it. Otherwise, the feed may not
be steady.

The same thing, really, as climb milling. OK if you have good leadscrews and
tight gibs, but pretty jumpy if you don't. With threading, the jumps wil give
you a wobbly thread.

John Martin

(JMartin957) wrote in message
...
I am reading various sources for information on threading in the
lathe. A lot is said about external threads, but not near as much
about internal threading.

For the moment, I am interested in cutting right-hand internal v
threads.

Various sources say to turn the compound 29.5 - 30 degrees to the
left. Disadvantage: No room to enter hole. Or leave compound to the
right and turn tool upside down. Or put compound in rear right
corner. Disadvantage: Have to lean over lathe to adjust. Other
permutations of these exist when the lathe is run backwards.
Disadvantage: Danger of unscrewing the chuck.

Why can't you just leave the compound set the same way as when cutting
external threads (29.5-30 to the right) with the tool in the normal
right side up position? The tool is still only going to cut on one
side. This time it will be mostly cutting on the rear side of the
tool and not the front as when cutting external threads.

Any thoughts would be greatly appreciated. Thank You



With the feed going the same way as the pressure from the cut, the tool may
tend to jump ahead a bit. Better to have the feed forcing the tool into
the
cut.

The easiest way to thread is with a cross slide stop, but the only way you
can
use one while internal threading is if you cut on the far side of the axis,
whether upside down or right side up.

John Martin

I use a cross-slide stop all the time while doing internal threading,
I don't use the stop screw, just the block. Move the bit until it
just touches the bore, zero everything, run the block up until it's
hard against the front of the cross-slide and have at it. I do have
to be careful when returning the cross-side after a cut that I don't
get carried away and bump the stop too hard, mine will shift a little
if I do that, I don't crank down hard on the dovetail lock. You do
have to get used to turning the cross-slide handle the opposite
direction, kind of like learning to drive on the other side of the
road. Works great, speeds up things a whole lot and I can make
repeated passes at the same setting without a lot of effort, improves
the finish a bunch. Takes a lot of the eyestrain out of threading,
you don't have to keep squinting at the dials to look for zero. One
of the better investments of time I've spent on the shaper. Made a
carriage stop at the same time, works great for threading.

Stan

Sorry 'bout that. My cross slide stop, which I made, works on the infeed
direction only. I'd temporarily forgotten that some can be set to work on
either infeed or outfeed. I agree with you about the usefulness of the stops
in threading especially.

John Martin

In article , John Albers
says...

Various sources say to turn the compound 29.5 - 30 degrees to the
left. Disadvantage: No room to enter hole. Or leave compound to the
right and turn tool upside down. Or put compound in rear right
corner. Disadvantage: Have to lean over lathe to adjust. Other
permutations of these exist when the lathe is run backwards.
Disadvantage: Danger of unscrewing the chuck.

Other approach for fine pitch threads, simply set the compound in
line with the lathe bed axis, and feed only with the crossfeed
screws. Disadvantage, the tool will be cutting on both
sides simultaneously. This works for finer pitch threads.

When I do this, I put the compound at the right rear quadrant.
You don't need to lean far to see what the dial is reading.

Jim

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(JMartin957)

Not to the center of the bore, but toward the headstock. You want the
cutting
force to be acting against the feed, not with it. Otherwise, the feed may
not
be steady.

The same thing, really, as climb milling. OK if you have good leadscrews and
tight gibs, but pretty jumpy if you don't. With threading, the jumps wil
give
you a wobbly thread.

I understand, and I like the comparison to climb milling.
What I was thinking (prompted by your post) was that the internal thread cutter
bounces not only ahead, but--because it's on a shaft behind it, rather than on
an arbor--moves also up and out of the cut.
But I like the comparison you've made.
FM