A couple threading questions

H

Hal

New member
What's a good way to end the threads on a barrel tenon when threading up to the shoulder?

Do you stop the lathe in the same spot and end up with an abrupt stop or is it better to stop the lathe .001 farther away from the shoulder on each threading pass. Ending up with a thread that tapers out?

When cutting threads with the compound set at 29 1/2° , do you cut to full thread depth or stop a couple thousands short and feed the cross slide in and clean up the shouder of the threads to a true 60° thread?

Thanks

Hal
 
Hal said:
What's a good way to end the threads on a barrel tenon when threading up to the shoulder?

Do you stop the lathe in the same spot and end up with an abrupt stop or is it better to stop the lathe .001 farther away from the shoulder on each threading pass. Ending up with a thread that tapers out?

When cutting threads with the compound set at 29 1/2° , do you cut to full thread depth or stop a couple thousands short and feed the cross slide in and clean up the shouder of the threads to a true 60° thread?

Thanks

Hal
Click to expand...

One way to do it is to cut a thread relief to stop the tool in. The way many do it is to position the tool where you want to stop the thread, about 1/16" or so from the shoulder then with a felt tip pin, make a mark on the way where the left carriage wing is. Then instead of watching the tool, watch that mark and then in a coordinated move, back off the cross slide and disengage the half nut at the same tile. Practice this for a few dozen times with the tool backed away from the tenon enough to miss the shoulder. You will be amazed as to how near the same spot you can stop the tool using this method.
 
I use two methods. Sometimes I cut a 1/8" thread relief groove and disengage the half nut when the tool reaches the groove then back off the cross slide one full handle revolution and move the carriage back for another pass.
Other times I cut the first pass up within about 1/8" from the shoulder, disengage the half nut, and leave the tool cutting for a full revolution to cut a thread groove then move a carriage stop and lock it down against the carriage. On subsequent passes I watch the carriage approach the stop and disengage the half nut just as it's about to touch, let the tool cut the groove deaper on each pass before backing off the cross slide.
I don't trust my co-ordination enough to back off the cross slide and disengage the half nut at the same time. (Can't walk and chew gum anymore)
Dave
 
As you disengage the carriage with one hand, back the tool out with the other. I thread in slow back gear & use a 1" indicator on the carriage to show when to stop. Set the indicator so it has one full revolution before you kick the tool out & stop the carriage. Works for me. Your mileage may vary!

Regards,
Ron
 
RJM said:
As you disengage the carriage with one hand, back the tool out with the other. I thread in slow back gear & use a 1" indicator on the carriage to show when to stop. Set the indicator so it has one full revolution before you kick the tool out & stop the carriage. Works for me. Your mileage may vary!

Regards,
Ron
Click to expand...

That is pretty much the way I do it, I can usually get within .005" on the indicator with each stop, MUCH more accurate than with a felt tip mark on the ways. On a mauser, or other with the receiver threads running all the way to the face of the receiver.

Jim
 
I gutted a micrometer stop for the mount, and I have a 2" travel dial indicator on it, via a mag mount. For threading, I set the tool a tad away from the shoulder, set the indicator to zero, then thread to "zero", disengage and back out.

I also use the same thing for cutting the tenon or anything else I need to measure, by touching the tool to the barrel breech, "preload" the indicator for the length of cut, and stop at zero. Works just like a trav-a-dial, but much cheaper.

Can't watch the numbers on a DRO threading, at least I can't.
 
My routine is to have the crossfeed zeroed with the handle top dead center. Then as I get to the shoulder I disengage the half nut and with my thumb hooked on the cross feed handle a quick twist of the wrist is all that's required to pull the tool out. I've threaded up to 300 RPM's that way. 200+ is walk in the park. Knock on wood I've never hit the shoulder yet.

Dave
 
RJM said:
As you disengage the carriage with one hand, back the tool out with the other. I thread in slow back gear & use a 1" indicator on the carriage to show when to stop. Set the indicator so it has one full revolution before you kick the tool out & stop the carriage. Works for me. Your mileage may vary!

Regards,
Ron
Click to expand...

Holey Cow, you just made my day!

Zero to Zero......!!!

duhhh


I've been just running up an indicator, finding my "stop point" and rotating my dial to zero. Sometimes my zero is near the top but not always and in any case I've never STARTED on zero, I just kinda let it start wherever, maybe 3/4 turn away, maybe even a turn and a half.... and I'm always all tense about "zero"....


"One Full Revolution" just make me smile. It's a definable thing, a finite time, a repeatable/learnable THING, like three seconds or something....

Ba-da-BING! Thank you :)

al
 
Al,
If you've every let your mind wander while threading, when that needle starts moving it will wake you up! Not that I ever day dream, so I'm only talking hypothetically of course. ;)
Regards,
Ron
 
RJM said:
Al,
If you've every let your mind wander while threading, when that needle starts moving it will wake you up! Not that I ever day dream, so I'm only talking hypothetically of course. ;)
Regards,
Ron
Click to expand...

I don't let it wander, it does it all on it's own

not hypothetically
 
It has been suggested to me by a gunsmith that I have a lot of respect for to use your DRO and zero it at the shoulder and then read it metrically. The numbers jump a lot slower.
 
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Gents,

I use the Sharpie mark on the ways method and haven't crunched one yet. I've spun it up to 250 rpm's with my carbide insert tool and it wasn't that difficult. I was a bit twitchy, though. I've since bought one of the Warner HSS insert tools for threading. I feel a lot better spinning 60 rpm's threading into a shoulder...and the threads turn out beautiful.

For the relief groove crowd. If your going to have a relief groove, why wouldn't you flip the tool and thread out from your groove? Is there some disadvantage I'm not seeing?

Justin
 
I'm still practicing on stubs - -

A friend, who is a tool & die maker, suggested that I use the relief groove method and turn my tool upside down then run the lathe in reverse, which I have been doing. I am running around 200 rpm. (South Bend 10L) This method keeps one away from crashes. Works slick, as far as I can tell, so far.
 
Pete,
The problem with any relief cut is when you need to extend the thread a bit more, the relief cut will be in the middle of the threads. Relief cuts force you to cut the whole thread off & start over which can be a problem when barrel is already short.

Flipping the tool over & threading in reverse put the forces trying to unscrew the chuck. Not a problem if you don't use a chuck with a threaded back.
Regards,
Ron
 
RJM said:
Pete,
The problem with any relief cut is when you need to extend the thread a bit more, the relief cut will be in the middle of the threads. Relief cuts force you to cut the whole thread off & start over which can be a problem when barrel is already short.

Flipping the tool over & threading in reverse put the forces trying to unscrew the chuck. Not a problem if you don't use a chuck with a threaded back.
Regards,
Ron
Click to expand...

With all the thread on a tenon, how could extending things a bit hurt anything? I surely would not cut the entire tenon off. These rifles aren't that ferocious, considering the size of their threads, are they? Regarding spinning a chuck off; As slow as one goes and as little as each cut takes, I don't see how one could loosen the fit between the face of the chuck backing plate and the spindle face. I tighten the chucks up tight to the spindle and the threads in my backing plates are a tight fit with the spindle's threads as well. Not had a hint of a problem yet, me.

Pete
 
I extended a tenon on a 338 Lapua Mag where the original relief cut ended up right in the middle of the threads. I would never do this on a customer's rifle but I did it on my own because I was playing with indexing. Barrel shot better and no issues.........Mechanically I can't visualize any issue except looks.

There are no support issues, no stretching/bulging/unequal loading issues.

It just looks funny

al
 
alinwa said:
I extended a tenon on a 338 Lapua Mag where the original relief cut ended up right in the middle of the threads. I would never do this on a customer's rifle but I did it on my own because I was playing with indexing. Barrel shot better and no issues.........Mechanically I can't visualize any issue except looks.

There are no support issues, no stretching/bulging/unequal loading issues.

It just looks funny

al
Click to expand...

One pointer on having thread reliefs in the thread body on a tenon, make sure to remachine the notch from a square one to "Vee" sided, 60 degrees, so you don't have that thin "feather" where the threads run out into the old notch. Those feather threads can wedge and lock up a thread joint.
 
JerrySharrett said:
One pointer on having thread reliefs in the thread body on a tenon, make sure to remachine the notch from a square one to "Vee" sided, 60 degrees, so you don't have that thin "feather" where the threads run out into the old notch. Those feather threads can wedge and lock up a thread joint.
Click to expand...

I have been cutting the relief cut deeper than the thread "root", if you will, to avoid that. I have seen several barrels over my BR career not lock up because of this, more so those that did not have a relief cut. They're hell on cases and seem to be teasers, accuracy wise. I have had a few barrels set back over the years and have come to the conclusion that it is not worth doing so, in that case, a relief cut, within reason, can be on the large side.
 
Pete Wass said:
I have been cutting the relief cut deeper than the thread "root", if you will, to avoid that. I have seen several barrels over my BR career not lock up because of this, more so those that did not have a relief cut. They're hell on cases and seem to be teasers, accuracy wise. I have had a few barrels set back over the years and have come to the conclusion that it is not worth doing so, in that case, a relief cut, within reason, can be on the large side.
Click to expand...

Pete, I'm not sure you and I are talking about the same thing. Think of the thread relief notch as a U and a thread profile as a V. The thread relief should have V sides regardless the grooves bottom shape or width.

As to whether these setbacks are worth it or not depends on the current barrel condition, is it slightly eroded or badly eroded, and, it also depends on the intended future use of the barrel being set back.
 
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