What I have Recently Learned About Chambering

[LVLAaron]

That setup will always bind. I will explain. As the the barrel pivots, the contact point changes. They are no longer straight across from each other. Even with the radius on the pads the contact points move off center and naturally want to straighten the barrel again. I dont like the ring but since the radius is smaller it will bind less. I hope you can picture what I am saying. I am not cutting down methods. I am just sharing what I have learned and hopefully its not taken the wrong way.

You're correct. Not taken the wrong way at all. The further from perpendicular the barrel is from the jaws the more binding there is.

The only way to totally eliminate that is with something like a true bore alignment system. 6 jaw and copper ring might do it less, but similar pressure in similar ways would apply. Same thing with an inboard spider. If the barrel is crooked, the inboard fixture is going to bend it.

This winter when things slow down I will do some tests with various setups and see if I can feel a difference by feeding pilots or slugs through the bore in situ and see if there is any measurable effect on the bore in it's setup.

 

[tac284]

@LVLAaron, what lathe do you have?

 

[Dusty Stevens]

@LVLAaron, what lathe do you have?

Harbor freight. I think its the bauer brand one.

 

[tac284]

Harbor freight. I think its the bauer brand one.

Eddie is really diversifying his portfolio these days..

 

[LVLAaron]

Harbor freight. I think its the bauer brand one.

@tac284 - PM1440GT 3 phase.

 

[boltfluter]

Really good thread guys, many ways to do this job. Always nice to see the creative things guys come up with. Carry on. Lol!
Paul

 

[Machinist John]

D1-4, direct mount to the spindle. Eliminates that thick 4 jaw chuck. The pads tilt & swivel. Pads are soft copper.

Started with a D-4 backplate.

 

[INTJ]

You're correct. Not taken the wrong way at all. The further from perpendicular the barrel is from the jaws the more binding there is.

The only way to totally eliminate that is with something like a true bore alignment system. 6 jaw and copper ring might do it less, but similar pressure in similar ways would apply. Same thing with an inboard spider. If the barrel is crooked, the inboard fixture is going to bend it.

This winter when things slow down I will do some tests with various setups and see if I can feel a difference by feeding pilots or slugs through the bore in situ and see if there is any measurable effect on the bore in it's setup.

I am not sure the TBAS would eliminate all the issues. Also, I can tell you from personal experience that having the barrel under a little tension doesn't mean it still won't shoot. It took me a while to figure out how to get the tension out, and some of my early barrels were chambered with tension but still winning group aggs.

You can often snug up an inboard spider or a 4-Jaw, then completely unload the outboard spider. You can then dial in the muzzle by hand and get it tension free. Then you can fine tune with the outboard spider re-engaged.

I don't think that is optimum, but it does greatly mitigate bending barrels.

I am still undecided on my chuck for work. The company will buy me any chuck I want to include TBAS. Right now the inboard spider is working well enough. I am leaning toward the inboard spider with the gimbal "jaws" that are pictured earlier in the thread.

 

[Machinist John]

Most of my work has been big bore hunting stuff where minute of Cape Buffalo is adequate.

Occasionally I strayed into longer range stuff:

So sometimes I will post about big bore applications, not the 1000 yarders.

And I am a retired old guy, quit building for hire some 25 years ago.

Current project (for me) is a 338 Win Mag, tang safety Ruger, for a horse back hunting rifle that will spend a lot of time in the scabbard packing into the Snake River Wilderness area.

 

[Machinist John]

Outside of the barrel needs TLC also.

 

[tac284]

I am not sure the TBAS would eliminate all the issues. Also, I can tell you from personal experience that having the barrel under a little tension doesn't mean it still won't shoot. It took me a while to figure out how to get the tension out, and some of my early barrels were chambered with tension but still winning group aggs.

You can often snug up an inboard spider or a 4-Jaw, then completely unload the outboard spider. You can then dial in the muzzle by hand and get it tension free. Then you can fine tune with the outboard spider re-engaged.

I don't think that is optimum, but it does greatly mitigate bending barrels.

I am still undecided on my chuck for work. The company will buy me any chuck I want to include TBAS. Right now the inboard spider is working well enough. I am leaning toward the inboard spider with the gimbal "jaws" that are pictured earlier in the thread.

What concerns do you have about the TBAC?

I have been using one for 5-6 years now and it has treated me very good. I do recommend you put it on as heavy a lathe as you can.

 

[Machinist John]

Back and forth, inside to outboard spider, eggshell touch, all the time keeping your eyes on the dial indicators.

Did this a few times but for the average elk rifle, not necessary. Different story for you gents shooting for money.

Made this 30 years ago for working with barrels that were too big for the spindle bore. Ball bearing on each end of the spindle. Works like a 4 jaw chuck.

Handy for a lot of things. Grinding the muzzle for a barrel band.

 

[xr650rRider]

I'm using an inboard and outboard spider. The aluminum pads are simply the result of using an annular hole saw. I have 0.200" thick .475" diameter on outboard side and 0.24" thick .562" diameter on inboard side. Spotted with 5/16" ball end mill, then drilled out with annular cutter. Ball is 5/16" and is 200 amp, very fast pulse tig tacked to end of 3/8"-24 set screw. They gimbal easily and I always part barrels and never had it slip. I didn't invent, just copying what I saw somewhere else. Wish I could give credit to original.

 

[INTJ]

What concerns do you have about the TBAC?

I have been using one for 5-6 years now and it has treated me very good. I do recommend you put it on as heavy a lathe as you can.

There are lots of complaints about chatter. Could be because it's really designed for a big lathe, not a 13-14" light/med duty lathe. Also, it's awfully long, meaning the length of barrel I can do without pre-threading the muzzle gets longer.

 

[tac284]

There are lots of complaints about chatter. Could be because it's really designed for a big lathe, not a 13-14" light/med duty lathe. Also, it's awfully long, meaning the length of barrel I can do without pre-threading the muzzle gets longer.

Yes, In my area we had a guy put one on a Jet 13x40 and he had chatter issues with his chambering. I never saw the setup only heard about it because a friend of mine bought it from him and put it in his Grizzly 14x40 gunsmith lathe, he has had no issues. I have mine on a 4800 pound machine so I haven’t had to worry about it.

I’m traveling right now but if I had to guess the TBAC will add around 10” from the spindle nose to the end of the jaws. Also depending on you’re maturity level (Age) it is a hand full. So if you’re taking it on and off that is something else to consider.

 

[Clark]

My chambering technique is devolving, but I am still getting great groups.