Dialing in bore for threading and chamber?

[Jeffrthehunter]

I plan on threading and cutting the chamber in my first barrel in a few weeks. Barrel is on its way (27" Bartlein 7mm #3b 5r). I plan on using a 4 jaw independent chuck and outboard spider assembly. I have seen several videos where they use a long pin with a bushing to remove bore run-out. I get the concept of checking different positions from muzzle to confirm the barrel is true. My question is why cant I use a test indicator (I have two that have .0001" graduations) and just confirm that the rifle lands are true (less than .0002" tir) at both ends? The chamber end at the chuck would be pretty easy and the spider end I may need a long mag base to reach. Not sure why it needs anything more than that? Am i missing something?

Thanks, Jeff

 

[shortgrass]

To begin with, the bore of a rifles barrel is not absolutely a straight line. Some are closer than others, with the Bartlien being very close. The critical part of 'dialing in' is to insure that the chamber is in line with the rifling where the bullet will enter. There are as many ways to accomplish this as there are gunsmiths.

 

[Danny1788]

This is overly exaggerated but the top picture shows why "I" don't dial in on the bore of both sides of the barrel.

The bottom picture shows why you only dial in on the breech and the I like to go another 2"+ further in and dial this area in. You have no control of what the bullet does when it is in the barrel it will follow the bore. All I want is the bullet to leave the case strait and strait lined up with the rifling.

On another side note make sure to use some type of shim or I use small brass rods in the four jaw chuck to the barre can pivot in the four jaw when dialing the bore in. I start at the chuck with the dti as far in as I can go. Then pull it back and adjust the outboard side. It takes practice but it's alot of fun to chamber your own rifles

 

[Jeffrthehunter]

View attachment 84363
This is overly exaggerated but the top picture shows why "I" don't dial in on the bore of both sides of the barrel.

The bottom picture shows why you only dial in on the breech and the I like to go another 2"+ further in and dial this area in. You have no control of what the bullet does when it is in the barrel it will follow the bore. All I want is the bullet to leave the case strait and strait lined up with the rifling.

On another side note make sure to use some type of shim or I use small brass rods in the four jaw chuck to the barre can pivot in the four jaw when dialing the bore in. I start at the chuck with the dti as far in as I can go. Then pull it back and adjust the outboard side. It takes practice but it's alot of fun to chamber your own rifles

Thanks for the pictures, makes perfect sense. So i just checked and there is a 1.750" X .080" stylist for my indicator. I would probably leave 2.00" of barrel exposed for cutting tenon and chamber. My indicator tip would not reach the area of what would be the throat, but I could at least true the breech end of barrel in two spots. Is this better that my original plan.
Thanks, Jeff

 

[Danny1788]

Thanks for the pictures, makes perfect sense. So i just checked and there is a 1.750" X .080" stylist for my indicator. I would probably leave 2.00" of barrel exposed for cutting tenon and chamber. My indicator tip would not reach the area of what would be the throat, but I could at least true the breech end of barrel in two spots. Is this better that my original plan.
Thanks, Jeff

Jeff I use an interapid Horizontal model 312B-15 with 2.75" long contact point

I usually set may jaws on my homemade barrel chambering fixture at the point where the contact point will be reading right where the pivoting feet of my fixture are. Then pull back and use the outboard spider.

 

[shortgrass]

In the big picture of things, chambering is nothing more than employing good machining practice. It is just careful thought procedures . It all starts before ever picking up a barrel. Lathe leveled to remove as much twist to the ways as humanly possible? Admittedly, the 'work', happens right up next to the head (if you chamber thru the head stock), but it is just good machine practice to have all straight as possible. Is the tail lined-up as close as you can get it, to the head? Type of tool holder. Is the chuck a direct mount or mounted to a back plate? Is that chuck a cheap piece, or a "real" piece of equipment? Cutting tool selection is equally important. These are all important considerations when setting-up any lathe, and not just for chambering. After all of that, there is no "right way" or "wrong way" to dial-in, as long as you get the desired result in the end is what matters.

 

[J E Custom]

In the big picture of things, chambering is nothing more than employing good machining practice. It is just careful thought procedures . It all starts before ever picking up a barrel. Lathe leveled to remove as much twist to the ways as humanly possible? Admittedly, the 'work', happens right up next to the head (if you chamber thru the head stock), but it is just good machine practice to have all straight as possible. Is the tail lined-up as close as you can get it, to the head? Type of tool holder. Is the chuck a direct mount or mounted to a back plate? Is that chuck a cheap piece, or a "real" piece of equipment? Cutting tool selection is equally important. These are all important considerations when setting-up any lathe, and not just for chambering. After all of that, there is no "right way" or "wrong way" to dial-in, as long as you get the desired result in the end is what matters.

What he said !!!!!!

J E CUSTOM

 

[Jeffrthehunter]

Jeff I use an interapid Horizontal model 312B-15 with 2.75" long contact point

I usually set may jaws on my homemade barrel chambering fixture at the point where the contact point will be reading right where the pivoting feet of my fixture are. Then pull back and use the outboard spider.

Thanks for the info, i use the same indicator for my CNC repair business. I will purchase that tip and give it a try.

 

[Jeffrthehunter]

In the big picture of things, chambering is nothing more than employing good machining practice. It is just careful thought procedures . It all starts before ever picking up a barrel. Lathe leveled to remove as much twist to the ways as humanly possible? Admittedly, the 'work', happens right up next to the head (if you chamber thru the head stock), but it is just good machine practice to have all straight as possible. Is the tail lined-up as close as you can get it, to the head? Type of tool holder. Is the chuck a direct mount or mounted to a back plate? Is that chuck a cheap piece, or a "real" piece of equipment? Cutting tool selection is equally important. These are all important considerations when setting-up any lathe, and not just for chambering. After all of that, there is no "right way" or "wrong way" to dial-in, as long as you get the desired result in the end is what matters.

Thanks for the thoughts. I just bought a Precision Mathews 1340 GT, my plan is to remove all twist and check all alignments (I repair CNC lathes for a living, aligning turrets, head stocks, and tail stocks after impact). At this point I am not sure whether to buy a good 3 jaw chuck and build a spider for both ends or use a 4 jaw. My concern is a spider fixture will not grip as firm as a four jaw, would hate to have something slip. Any thoughts?

 

[shortgrass]

With 40+ years of machining experience, I have made a few machine repairs/re-alinements myself. I've seen some horrendous crashes. That said, The spider some build to replace the chuck with worries me. Possible slippage. Some wrap a heavy copper wire around the barrel shank and this allows the barrel to pivot in the 4 jaw when dialing-in the bore. There are other ways of "getting there", if you think about it. In my way of thinking, some way over complicate the process, and are firmly convinced that "their way, is the only way". If a guy is a machinist to begin with, and takes the time to think it through......

 

[Edd]

.......... There are other ways of "getting there", if you think about it. In my way of thinking, some way over complicate the process, and are firmly convinced that "their way, is the only way". If a guy is a machinist to begin with, and takes the time to think it through......

How do you dial in a barrel?

 

[Pdvdh]

Tagging in because I enjoy these technical & trade secret threads. It's secret to me. Never run a lathe in my life...
Watched my brother run one. Makes me dangerous. I'd like to run one, but no way to justify the costs at this stage in life.

 

[shortgrass]

How do you dial in a barrel?

I use a Pratt Burnerd 4 jaw chuck and a dial indicator.

 

[Trickymissfit]

Thanks for the pictures, makes perfect sense. So i just checked and there is a 1.750" X .080" stylist for my indicator. I would probably leave 2.00" of barrel exposed for cutting tenon and chamber. My indicator tip would not reach the area of what would be the throat, but I could at least true the breech end of barrel in two spots. Is this better that my original plan.
Thanks, Jeff

just changing the stylus on a dial indicator will change the readings. That's why an indicator with a long stem will have a different part number. My suggestion would be to find one you can borrow that came with the long stem. I have a pair of Interrapids that look identical except for the wands, but if you change the stylus they read differently when checked over gauge blocks.

Lastly when dialing in the bore, never turn the indicator upside down unless your using an Interrapid or B&S Best Test. Rest will develop lag.
gary