Threading Barrel

L

Larry Wilkins

Guest
OK,Gents, Here is the task.
Have a new barrel in 40x chambered for 7 Mag and wish to set same back and chamber for 7 WSM.
Question? Cut off .550, pick up the thread and re-chamber for 7WSM.?
Is ther a problem picking up the existing thread??

Thanks

Cheers, Larry
 
Picking up an existing thread is easy. First item is to get the old barrel running true by indicating it in. Then set your lathe up to thread 16 TPI. Back out on the crossfeed until the threading tool cannot touch anything then engage the half nut so the lathe is in gear. Let it run until it's to where the threading tool is where the threads would be if it were touching. Turn off the lathe but leave the half-nut engaged. When the lathe stops run the crossfeed in until the threading tool almost touches the thread then by working the compound set at 30 degrees and the cross feed as needed the point of the threading tool is in the bottom of a thread. Set the crossfeed at '0' and the compound at whichever number you choose. Then disengage the half-nut and back out on the crossfeed so you can move the saddle away from the headstock.

This making any sense to you? I don't know if I've done a good job of explaining it but I learned to do this while in machine shop class just by looking at it and it just came to me how to do it. It will become apparent to you when you study it for a minute or two.

Holler if you need help.
 
MColeman said:
. . . Then disengage the half-nut and back out on the crossfeed so you can move the saddle away from the headstock. . .
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Mickey

Don't you mean back out the compound?? If you back out the crossfeed the point of the tool will be at the center of the V when you start to extend the thread.

Ray
 
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W

My head was hurting too.:D

If you backed out the crossfeed you COULD cut the new part of the thread with a straight-in cut but that usually causes chatter. But, if you did it that way there would be no need for the compound to be set at 30 degrees (or any other angle) and you needn't zero the dial because you won't be touching the compound.

PS - It looks like we were posting at the same time and said the same thing. Great minds really do think alike.

Right???

Ray
 
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Cheechako the compound needs to be set at 291/2 or 30 degrees. If you don’t you can’t pick up, chase and extend the thread. It is best in my opinion to use the compound to cut the tread to depth. The cross slide feed method results in a V shaped chip that is hard to control or break and tends to lead to more tearing of the finish on the thread. Set the cross slide to zero so that you can roll out of the cut as you disengage the half nut. This results in a very professional looking trail out and the end of the thread instead of a thread relief. If you leave a thread relief you should remove it when you set back the barrel which means you loose the whole tenon in stead of just the throat section of the chamber.

Mickey was correct. You can set the cross slide to zero, back it out, run the carriage to the right, roll out one half or the double thread depth as listed on your threading gauge from the compound and get the job done from there. This is assuming that you engaged your thread chasing dial and then the half nut on the correct number when you started.

Nic.
 
Nic

I'm not advocating that you cut the thread with a straight in cut with the cross slide. In fact, just the opposite. I was saying that if you wanted to do it that way there was no need to set the compound at any particular angle since you would not be using it anyway.

It seems to me that setting up as Mickey said but backing out the compound is the quicker way. You then feed with the compound as per a normal thread cut, returning the cross feed to "0" each time.

I think we simply have a different way of expressing how we get there.:)

And having a relief cut doesn't necessarily mean that you lose the entire tenon with a setback. You can thread right over the relief cut. It does look like hell but nobody but you knows that it's there when the barrel is screwed into the action.

Ray
 
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Let me clarify this a bit......

If you're going to set the shoulder back say, 1/2 inch, then you have to cut the tenon to size but the 1/2 inch is not threaded. To pick up the thread follow the first post but when you back out on the crossfeed to move the carriage to the right to clear all threads you then move..........you guys are making my head hurt. :)

After you have chased the existing threads and have the crossfeed set at '0' you obviously can't cut the new threads in one pass so you move the carriage to the right and set the crossfeed at '0' and then you have to back out on the compound enough to keep from cutting the new threads in one pass.

I always zero out my compound and crossfeed when cutting new threads and by the time the compound gets close to .040 the threads are almost done. If I were chasing threads and had the point of the threading tool in the bottom of the threads I would zero out the crossfeed and set the compound on .040 and then back it all out and start the new threads with the compound set first at .005 and then advance it as needed but always have the crossfeed set at '0'.

Reckon we oughta give him the suicide hotline number? It's a lot easier than we've made it sound so take heart.
 
MColeman said:
After you have chased the existing threads and have the crossfeed set at '0' you obviously can't cut the new threads in one pass so you move the carriage to the right and set the crossfeed at '0' and then you have to back out on the compound enough to keep from cutting the new threads in one pass.
Click to expand...

Mickey that's what Ray and I were discussing but we each had a different way of saying it. This is something that you do almost without thinking about it but to try to explain in words, well that's the difficult part.
 
WSnyder said:
Mickey that's what Ray and I were discussing but we each had a different way of saying it. This is something that you do almost without thinking about it but to try to explain in words, well that's the difficult part.
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Exackly!
 
The threaded tenon on a Rem is normally only .700" long. Why would you go to the trouble of picking up the existing thread to save .150" of barrel length? Am I missing something?
 
J. Pendergraft said:
The threaded tenon on a Rem is normally only .700" long. Why would you go to the trouble of picking up the existing thread to save .150" of barrel length? Am I missing something?
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He might have to set it back 1/2 inch to get the WSM reamer to clean up the 7 mag chamber....
 
MColeman said:
He might have to set it back 1/2 inch to get the WSM reamer to clean up the 7 mag chamber....
Click to expand...

Larry said he was taking off .550" so my point is why not take off .150" more (.700" total) and have an entirely new thread. Actually I would look at what it takes to give an entirely new neck and throat in the rechamber and do that if possible.
 
J. Pendergraft said:
Larry said he was taking off .550" so my point is why not take off .150" more (.700" total) and have an entirely new thread. Actually I would look at what it takes to give an entirely new neck and throat in the rechamber and do that if possible.
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Valid point.
 
The thread portion may only be .700 but the length of the tenon is about .880
 
Jkob said:
The thread portion may only be .700 but the length of the tenon is about .880
Click to expand...

The original question was about picking up the existing thread. The unthreaded portion of the existing tenon can remain as part of the new threaded tenon.
 
Picking at nits here, but the tenon length also depends on the thickness of the recoil lug and whether or not a lug is actually used.

Also, the original question was "how to pick up an existing thread". It's not for us to tell him how he should do his project differently than what he proposed.

JMHO

Ray
 
Picking up thread

To all, Thank you or all the imput.
MColeman, Am maybe more Senior, but am trying to learn metal work at the Local Jc. All given has been printed out and will see what comes of all your efforts. Didn't have info on tenion, so will have to look up same. Maybe one of you have a direction to such.
Thanks all.
Cheers

Larry
 
Larry Wilkins said:
To all, Thank you or all the imput.
MColeman, Am maybe more Senior, but am trying to learn metal work at the Local Jc. All given has been printed out and will see what comes of all your efforts. Didn't have info on tenion, so will have to look up same. Maybe one of you have a direction to such.
Thanks all.
Cheers

Larry
Click to expand...
Troy Newlon of Newlon Precision (Benchrest Central advertisor) has a book of most, if not all, common rifles you'll encounter. He gives all dimensions of barrel tenons, threads and headspace measurements. It's not free but it's not outrageous, either.
 
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