Lathe chuck setup

[ScottMcc]

I assume gunsmiths use a 4 jaw chuck for precise runout control, right? What about cutting soft jaws for each particular barrel with a 3 jaw chuck? I have both chucks available, but dialing in a 4 jaw is a bit of a pain. Also, getting low runout at the end in the chuck is no problem, but what about the opposite end? I mean say you are chucked up nice and straight on the chamber end, but how do you know the muzzle end is still true along the bore axis? thanks, scott.

Edit: I just realized I have a collet chuck available too. Not sure if it will go to 1.25, but I will find out.

 

[ScottMcc]

Come to think of it, you need to zero in on the bore centerline, rather than the ouside dia of the blank. So the 4 jaw is really going to be the best way to go, right?

 

[Erik Cortina]

Come to think of it, you need to zero in on the bore centerline, rather than the ouside dia of the blank. So the 4 jaw is really going to be the best way to go, right?

Yes, indicate on the bore, never on the outside diameter.

Some use an outboard spider to indicate the muzzle end as well. Some do it through the headstock, some on a steady rest, and some use a combination of both.

There are different ways to remove the outer flesh from a feline! ;D

 

[ScottMcc]

Great, thanks. The spider basically holds the loose end of the barrel cantered in the headstock? I often use plastic bushings in the end of the headstock to control whipping. Does it need any additional truing other than holding the material centered in the headstock?

 

[Erik Cortina]

This will give you an idea of how it works.

You use the outboard spider to indicate the barrel as well as the 4 jaw.

 

[STS]

Here is another little issue for you to loose sleep over. If you grip your barrel directly in the jaws of any chuck the flat to flat contact will not allow the barrel to pivot enough to align the muzzle without flexing the barrel. You can dial in the muzzle end all you want and the bore ahead on the chamber will still have some runout. I use a heavy piece of copper wire (#10 I think) positioned on the barrel right where the throat will be. I allows me to get the blank in the spindle straight and without flexing. You can also use a catshead type holder on the chamber end of the barrel and achieve the same thing. I use a catshead on short barrels.

 

[ScottMcc]

Erik, I looked up a vid and figured it out - tube with 4 tapped holes with bolts to center the barrel bore. Now what is the proper way to indicate off the bore? My thought is to centerless-grind a brass rod until it fits the id perfectly, long enough to go in a few inches and sticks out enough to get the indicator on.

STS, you use a single turn of copper wire around the outside so it clamps between the barrel and jaws? Do you use a lathe dog for torque?

 

[Erik Cortina]

Sorry, forgot to post link to video earlier.

http://www.youtube.com/watch?v=5TrcgvFEtTE&list=UUyikBF6Tklx_dP8ENRFhRYg&index=8

You need range rods to indicate bore.

But if you have $200.00 you are better off sending it to an experienced gunsmith.
My $.02

 

[X Ring Accuracy]

If you have a lathe, which I assume you do. You can make your own brass "range rods". The trick is tapering / stepping them for different bores in the same caliber.

 

[GNERGY]

Watch these and it will give you a good idea how to do it. I watched these before I did my first chambering job, it was a Krieger barrel chambered to 6.5 WSM and it came out perfect the first time. Those are the 2 best chambering videos out there.
Hope this helps.
http://www.youtube.com/watch?v=ErVOUVszFjY
Tarey

 

[ScottMcc]

Thanks guys! I watched over 2 hours of videos, mostly around Erik's link to suar08-something's vids on threading and chambering and truing the 700 action. I take away several lessons: 1, I wasted about $100 on gunsmithing books including "accurizing the factory rifle" and none of them showed the proper way to jig and index a barrel or action. 2, It takes so much work to true a 700 action that custom actions of $1000+ seem pretty darn reasonable. And 3, I like the hard way, and this was just what I needed. I work at a job shop with 6 cnc machines and several manual machines. I'm going to find a cheap 700 on backpage, and order a barrel and some tools, and have a great time building a rifle.

 

[Erik Cortina]

With a CNC lathe, you can just do this! ;D

http://www.youtube.com/watch?v=fjWHcO3Gq_w

 

[STS]

Scott, No lathe dog is needed. There is enough friction between the copper wire and the barrel to keep things from slipping. I usually chamber 2 barrels with one piece of wire and then throw it away as it gets flats on it from griping the barrel. I make ten or twelve rings at a time so I have one when I need to do a barrel.

 

[STS]

With a CNC lathe, you can just do this! ;D

http://www.youtube.com/watch?v=fjWHcO3Gq_w

I have seen that chuck before. It's a portion of a sphere mounted to a mating surface back plate. About as slick of set up as I have ever seen and if I did this stuff for a living I'd get one. I don't recall the price but $1600 rings a bell. The other top end method is thread milling. A CNC mill can whip out a perfectly trued action in minutes.

 

[ScottMcc]

Daaang Erik, that was slick. A regular 3 jaw scroll chuck is $2-3K so I would guess that swivelly angular one is $5k+. Very cool, thanks guys!