Dialing in bore for threading and chamber?

[bigngreen]

I'm running a PM 1340GT, think you'll like it, I've been very pleased with mine and the support was excellent, it's a sweet lathe for gunsmiths!!
I made a steel ring that is curved on one side to allow the barrel to gimbal along with the 4 jaw, copper wire wrapped works but if you watch it it'll move through the job and takes minor tweaking. I'm going to remake a chambering Chuck using a thick back plate and making a spider that uses small v blocks, my buddy uses this set up and it puts no stress on the barrel and allows easy dial in yet holds it extremely secure.
I have played and tested all the popular methods of dialing in and the range rods are only repeatable to a couple thousand, the direct read is the only method that is really a known and can't be influenced, when chambering longer cases I use the Grizzly rod in the throat and in testing I found it very accurate and repeatable WITH experience, though I check with a dti to assure I'm dialed.
Gunsmithing is just BASIC machining that goes bang in the end!!!

 

[Jeffrthehunter]

I'm running a PM 1340GT, think you'll like it, I've been very pleased with mine and the support was excellent, it's a sweet lathe for gunsmiths!!
I made a steel ring that is curved on one side to allow the barrel to gimbal along with the 4 jaw, copper wire wrapped works but if you watch it it'll move through the job and takes minor tweaking. I'm going to remake a chambering Chuck using a thick back plate and making a spider that uses small v blocks, my buddy uses this set up and it puts no stress on the barrel and allows easy dial in yet holds it extremely secure.
I have played and tested all the popular methods of dialing in and the range rods are only repeatable to a couple thousand, the direct read is the only method that is really a known and can't be influenced, when chambering longer cases I use the Grizzly rod in the throat and in testing I found it very accurate and repeatable WITH experience, though I check with a dti to assure I'm dialed.
Gunsmithing is just BASIC machining that goes bang in the end!!!

Thanks for the info, after much reading I will purchase a Grizzly rod with the .284" bushing set. I also will also order the Bison 4 jaw chuck from Grizzly (looks better that the China stuff). I am planning on making a aluminum sleeve 1/4" long that will clamp between jaws and barrel, if it wont dial in I will try something else. Can I go to tight on the 4 jaw chuck?
Thanks, Jeff

 

[bigngreen]

How tight you go is by feel but you can get them tight enough that when you remove the barrel you end up with a distorted chamber but with your experience I doubt you'll have an issue. Believe it or not a 1/4 sleeve will not allow the movement you need, you will be forcing the barrel and putting a bend in it to get it aligned then during operation it will relieve and move, even with my radiuses ring I have to watch it. If you use a strategy to hold the barrel that in parts no stress to dial in you'll find dialing them in is quick and easy and it stays.

 

[J E Custom]

I made my self a 4 screw Spider with brass inserts in the screws for the tail of the spindle and dial the muzzle in the same way I dial the shank end of the barrel but it does take two rods at the same time and two dial indicators.

Once I get the barrel dialed in on both ends it never comes out of the lathe until all threading and chambering is done. the spider seems to hold the barrel very well and stays in alignment.

While I'm set up I also check the od of the barrel, and if it is not true to the bore, I re-contour between centers so that everything is symmetrical
and true to the bore. Some say this is not necessary, but I don't mind the extra time in order to end up with everything as near as perfect as "I" Am capable of.

Just the way I do it

J E CUSTOM

 

[Danny1788]

here is my headstock cat head that I machined the 3/8x16 cap head screws with a 1/4" ball bearing.

Then I made some small steel v blocks and machined a 1/4" seat with a ball end mill. This way the v blocks pivot but apply a rock solid holding force.

this is the setup holding a barrel.

Like BIGNGREEN said this has help my chambering out a lot, I got this idea from Alex Wheeler he is an awesome gunsmith and super nice guy.

 

[bigngreen]

That's awesome, Alex is a good friend of mine and I was amazed when we played with that kind of chucking strategy how well it allowed the barrel to move yet when tight how secure it is, the outboard spider really doesn't have to force the barrel like most other methods.

 

[Jeffrthehunter]

here is my headstock cat head that I machined the 3/8x16 cap head screws with a 1/4" ball bearing. View attachment 84421

Then I made some small steel v blocks and machined a 1/4" seat with a ball end mill. This way the v blocks pivot but apply a rock solid holding force.
View attachment 84422

this is the setup holding a barrel.
View attachment 84423
View attachment 84424

Like BIGNGREEN said this has help my chambering out a lot, I got this idea from Alex Wheeler he is an awesome gunsmith and super nice guy.

Thanks for the write up and pictures, very nice fixture! Have you had any slippage?

 

[Danny1788]

Thanks for the write up and pictures, very nice fixture! Have you had any slippage?

Havent had any issues with the barrels slipping at all, the reason I ended up changing my setup was because I came to the conclusion I was bending the barrel and forcing it into what I thought was true, once the clamping force was released I would have a small amount of chamber runout, These pivoting vblocks fixed my setup issues.

Like BigNGreen wrote above I don't even use my outboard spider to move the barrel I get the throat running true and use small amounts of push and pull on the muzzle by "hand" to get the back breech running true then just snug up my outboard spider and check my throat again. Usually I have to make small adjustments back and forth but I'm not force the barrel into place anymore.

 

[Canadian Bushman]

Calhunter805,

How are you holding your reamers?

 

[TwoMore]

Thanks for the info, after much reading I will purchase a Grizzly rod with the .284" bushing set. I also will also order the Bison 4 jaw chuck from Grizzly (looks better that the China stuff). I am planning on making a aluminum sleeve 1/4" long that will clamp between jaws and barrel, if it wont dial in I will try something else. Can I go to tight on the 4 jaw chuck?
Thanks, Jeff

I am Far from a Master but I am in the same group a lot of us are in ,, I tried an aluminum sleeve that I tapered both sides to a point in the center inside for the barrel to pivot in but it only fits certain blanks, I use the copper wire mainly now, I use range rods to rough in the bore then move to the Interapid 312b-15 indicator. I used to indicate the bore at the wire on the 4 jaw then move out to the end and use the rear spider to adjust there but I changed to indicating in the throat area and then the neck area to try to get a straighter chamber entering the bore. ( I would love to hear others indicating methods) This usually leaves a bit of run out at the end but I pre-bore the chamber and that takes care of that. and the 2 hours of reaming lol. dont forget to time the muzzle high side up with the action I really like the way that v block system looks, I need to try that for sure here is a pic of the aluminum pivot bushing I use , like I said i like that v-block system. thanx for showing us that

 

[TwoMore]

I Dial in my tail stock and use a center on my reamer holder that I modded , I dont care for floating reamer holders. I have tried a couple different ones and just didnt like the feel and the ability for the rear of the reamer to shift and bite.

 

[TwoMore]

here is my headstock cat head that I machined the 3/8x16 cap head screws with a 1/4" ball bearing. View attachment 84421

Then I made some small steel v blocks and machined a 1/4" seat with a ball end mill. This way the v blocks pivot but apply a rock solid holding force.
View attachment 84422

this is the setup holding a barrel.
View attachment 84423
View attachment 84424

Like BIGNGREEN said this has help my chambering out a lot, I got this idea from Alex Wheeler he is an awesome gunsmith and super nice guy.

thats a beautiful finish on that breech are you threading with a brake?

 

[Jeffrthehunter]

I am Far from a Master but I am in the same group a lot of us are in ,, I tried an aluminum sleeve that I tapered both sides to a point in the center inside for the barrel to pivot in but it only fits certain blanks, I use the copper wire mainly now, I use range rods to rough in the bore then move to the Interapid 312b-15 indicator. I used to indicate the bore at the wire on the 4 jaw then move out to the end and use the rear spider to adjust there but I changed to indicating in the throat area and then the neck area to try to get a straighter chamber entering the bore. ( I would love to hear others indicating methods) This usually leaves a bit of run out at the end but I pre-bore the chamber and that takes care of that. and the 2 hours of reaming lol. dont forget to time the muzzle high side up with the action I really like the way that v block system looks, I need to try that for sure here is a pic of the aluminum pivot bushing I use , like I said i like that v-block system. thanx for showing us that

To make sure I understand??? If the bore has a bow (they all will to some degree) you should time the action so the the barrel shoots up 12 o'clock. Another question, PTG is the only company the has a rotating piloted reamer in stock (for 7mm RM), is that the way I should go?

Thanks,

Jeff

 

[Danny1788]

thats a beautiful finish on that breech are you threading with a brake?

No I thread on a manual lathe with HSS inserts. no foot brake or anything like that. holding the barrel rigid and having the right threading tool makes a big difference in surface finish