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Threading barrels

Dusty Stevens said:
Everything is soooo simple.
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It was funny because guys in the shop, including my boss, were trying to give me an out. I finally told them it was 100% my fault. The belted mag go gauge hung up on the belt during my check before my final cut. I should have caught it but didn't. Had I not blindly cut the relief groove I could have easily fixed it.

Chambering barrels does require focus and thinking.........
 
You guys with all your fancy stuff. I've got a SouthBend Heavy 10. Older than I am and I'll not be competing with anyone when it comes to completion times but it works just fine. And I have the satisfaction of doing it myself.
To each his own reward.

It did come from the Des Moines Army Ordinance plant, so that's kinda cool. :cool:
 

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I turn tenons down with this.
22-12-21 18-03-13 9269.jpg
Once I get to my finished diameter I clean up the shoulder and then plunge enough to reach the minor diameter of what will be the thread. It gives me a small "chicken groove" but enough room to get the threading tool out.

I always clock my barrels to 12 o'clock so the shoulder will get a little more work when the threading is done.

If I need to set it back later, I'll move the shoulder up a thread. Total chicken groove ends up being small enough to not worry about.


1671664278639.png
 
INTJ said:
I have a Mark Jacobs control board and micrometer stop for the PM1340 GT I have at home. I don't use it much. I don't if it stops fast enough to thread into a groove. I should try it though.....
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If your vfd braking is set up good itll stop on the same degree of rotation running as fast as your spindle can turn
 
LVLAaron said:
I turn tenons down with this.
View attachment 1394191
Once I get to my finished diameter I clean up the shoulder and then plunge enough to reach the minor diameter of what will be the thread. It gives me a small "chicken groove" but enough room to get the threading tool out.

I always clock my barrels to 12 o'clock so the shoulder will get a little more work when the threading is done.

If I need to set it back later, I'll move the shoulder up a thread. Total chicken groove ends up being small enough to not worry about.


View attachment 1394192
Click to expand...
That looks real good, but like me and jackie is saying to clean up a throat to make a good barrel last longer we may only extend it out .050-.100 so any chicken groove will start getting into your threads. On a muzzle do whatever, but ive never seen an action that needed a thread relief so i dont do it. May crash the shoulder tonite but i havent in many years
 
I feel ya. That one was set back a thread (55 thou) - the groove is just shy of the minor diameter so it fits into the threaded part of the action.

Knock on wood, don't crash it!
 
Ksracer said:
Relief grooves serve another (probably more important) purpose other than a place to stop the tool.

Most muzzle devices simply have a chamfered starting thread. If you thread a muzzle without a relief groove, you'd better get really close to that shoulder or it's going to run out of thread and bind before it hits the shoulder. I've had to turn galled suppressor mounts off before because somebody else thought it looked cool to skip the thread relief.

You'll find a few devices with a counterbored female thread, but it's the exception, not the rule.

The same applies to actions with integral recoil lugs, although there is usually more wiggle room. It's not an issue with individual lugs because you can simply thread far enough that the lug covers your stopping point.
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This.
Harrell's only recently started counterboring their brakes- prior to that, thread relief in the tenon was mandatory.

Since this is for the inexperienced OP...
The 60 degree shape of the threading tool/insert obviously means it gets wider as you move away from the tip. With finer thread pitches, the depth of thread is not very deep- meaning, you can get closer to the shoulder- and perhaps not need a relief cut. With coarser threads, like common 16 TPI for barrels- the depth of thread is much deeper, and you cannot get right up to a shoulder without the left side of the cutter crashing into the shoulder and ruining your work. With HSS, you can grind away some of the left side of the cutter beyond the point that's needed for the depth of thread being cut allowing you to get closer. Full profile inserts get you very close to the shoulder, but that's another ballgame...

When I first started machining a decade ago- mostly self taught- I noticed there is often this "I don't need no stinking relief groove" mentality as though it's some sort of badge of honor. Bullshit... if I've got the room for one, I cut it. Sometimes on very short brake tenons I don't want to lose those couple of threads of engagement so I won't do it- but don't think that relief cuts are for "amateurs".
 
INTJ said:
I have a Mark Jacobs control board and micrometer stop for the PM1340 GT I have at home. I don't use it much. I don't if it stops fast enough to thread into a groove. I should try it though.....
Click to expand...

I bought the proximity sensor but never used it as I thread away from chuck and proximity sensor became unnecessary. Using the default carriage stop when you use an inboard spider, there isn't enough physical space to use it unless it was mounted on the carriage. You could if you use a chuck. If your using the Hitachi drive, I think the braking speed was frequency dependent, so the recommendation for faster stopping was to keep the drive at a lower frequency and adjust RPM with gearbox. Lower the HZ, the faster it stopped.
 
tobnpr said:
This.
Harrell's only recently started counterboring their brakes- prior to that, thread relief in the tenon was mandatory.

Since this is for the inexperienced OP...
The 60 degree shape of the threading tool/insert obviously means it gets wider as you move away from the tip. With finer thread pitches, the depth of thread is not very deep- meaning, you can get closer to the shoulder- and perhaps not need a relief cut. With coarser threads, like common 16 TPI for barrels- the depth of thread is much deeper, and you cannot get right up to a shoulder without the left side of the cutter crashing into the shoulder and ruining your work. With HSS, you can grind away some of the left side of the cutter beyond the point that's needed for the depth of thread being cut allowing you to get closer. Full profile inserts get you very close to the shoulder, but that's another ballgame...

When I first started machining a decade ago- mostly self taught- I noticed there is often this "I don't need no stinking relief groove" mentality as though it's some sort of badge of honor. Bullshit... if I've got the room for one, I cut it. Sometimes on very short brake tenons I don't want to lose those couple of threads of engagement so I won't do it- but don't think that relief cuts are for "amateurs".
Click to expand...

Instead of grinding a threading bit, I provided the requirement to ThinBit to thread closer to the tenon shoulder. After a few discussions, here is what we agreed on, made from carbide. They sold me just the minimum quantity order.

Screenshot_20210728-132133_Adobe Acrobat.jpg

Brother paid for them, use them exclusively on his VFS barrels
 
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I do ~29.5 using the compound and thread right up to the shoulder (no relief cut) with a carbide lay down style bit. I use the cross slide to withdraw the bit at the end of the cut at the same time the half nut is disengaged. Then take the bit back to the start, turn the cross slide back to zero, advance the compound slide and wait for the number to roll around to start the next pass. It takes a bit of practice to develop the muscle memory but the argument is that the relief cut is a weak point in the barrel. And yes, no doubt, there is a bit of snob appeal in threading right up the the shoulder. I use a plunge style dial that I setup to count down to zero where I end the thread. Takes a lot of focus. I do this based on advise from people who chamber their own barrels and who have won US Nationals. Can't argue with success.

Also when I'm cutting I do my scratch pass at about 5 thou. Then 10 though until I get within 20. At that point drop to 5 until I get within 5. Then 2 and finally 1. I also run the final passes twice at the same setting and start testing the thread when I'm about 3 thou off what it should be. I don't usually make it all the way to the depth that is recommended in the Machinery Handbook. I like a tight thread and find that I usually get what I'm looking for before I reach final depth.

The reason you do 29+ with the compound is that with a 60 degree thread, you are only cutting half of the thread and maybe just a tiny bit of the other half of the v. Why would you do this? Cut a deep thread by going directly in and look at the shape of the chip. Then look at the quality of the cut. Then consider the heat associated with plunging the cut so both sides are cutting at the same time. ~29 degrees creates a much better thread and chips that actually break cleanly without the heat. Never heard of anyone plunge cutting threads with the cross slide. That's what the compound is for.
 
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