Chambering short barrels in the headstock

[LVLAaron]

PM1440GT owner. Shortest barrel I can get between the chuck and outboard spider is ~24" which is fine for most cases... But I plan on making custom AR barrels in the 18-22 inch range.

I'm sure this wheel has already been invented... But it doesn't seem unreasonable for me to be able to make some round stock with a clamping feature on one end to hold the short end of the barrel to extend it to the outer spider.

Am I crazy? Is there a better procedure?

 

[Jason812]

Use the receiver truing fixture you building.

 

[mickri]

Chamber your barrel between centers.

 

[LVLAaron]

Chamber your barrel between centers.

... No

 

[Firebrick43]

Chamber your barrel between centers.

You cant chamber between centers, the center would block the reamer!.

You can use a chuck and a steady rest. If your going to do a lot of short barrels, build a spider bearing steady rest. They steady uses a larger 2 bolt pillow block bearing. Locktite a heavy sleeve in the bore that is drilled and tapped for brass tipped set screws. Treat it just like any other spider but the barrel end will be in the chuck and the chamber end at the steady spider.

I think you will find anything that threads/clamps to the end of the barrel is going to have issues with axial alignment and radial runout.

Really short barrels like pistol barrels, you can place a center in the head stock bore and then the chuck on(if your lathe can do that) some cant. the barrel is held entirely in the chuck with shims at a small point. The muzzle pushed against the center.

 

[mickri]

It is common knowledge that the term "chambering between centers" refers to a process where the barrel is first held between centers to turn the shank to the proper diameter and is then threaded. The threaded portion of the barrel is next placed in a steady rest, the tailstock center is removed and replaced with the reamer. The reamer held in the tailstock effectively becomes the center as it cuts the chamber. Here is a link to a thread on PM where gunsmith Rod Henrickson aka spearchucker30x378 explains the process. https://www.practicalmachinist.com/vb/gunsmithing/chamber-reaming-between-centres-230343/ Rod is a highly respected gunsmith.

There is an ongoing debate over which way is better. Between centers or through the headstock. I personally do not have an opinion one way or the other. My lathe does not have a big enough spindle bore to chamber through the headstock. So I will be doing my chambering between centers following Rod's method.

There are many variations on how to thread and chamber a barrel. Too many to describe here. The consensus I have found seems to be to do what works for you with the equipment that you have. One variation that I have seem that may work for LVLAaron is to machine a long dead center held in the spider on the outboard end of his lathe to center the muzzle end of the barrel and then dial in the chamber end in the fixture that he has made.

 

[Ken226]

I used to use the chuck and steady method for shorter barrels.


As Jason mentioned:

Use the receiver truing fixture you building.

A receiver truing chuck is very handy for short barrels. You can indicate the bore to center with a range rod.



I milled some big slots in mine to clear the bolt handle, so I can use it for bolt work.

 

[LVLAaron]

I used to use the chuck and steady method for shorter barrels.


As Jason mentioned:


A receiver truing chuck is very handy for short barrels. You can indicate the bore to center with a range rod.



I milled some big slots in mine to clear the bolt handle, so I can use it for bolt work.

Any chance you have a drawing of that beautiful piece? What kind of material did you use?

 

[Ken226]

Any chance you have a drawing of that beautiful piece? What kind of material did you use?

I had an Inventor drawing for it, but last year I switched to Alibre Design for my CAD software, and have since lost many of my Inventor files.

Which is too bad, because I recently upgraded to Alibre Design Expert, which can open and use Inventor files.


The material was a 6" long piece of 4-3/4" diameter 8620 hot roll from eBay. I used a d1-4 back plate from Shars. I think I was into the whole thing for just over 120$

 

[LVLAaron]

I had an Inventor drawing for it, but last year I switched to Alibre Design for my CAD software, and have since lost many of my Inventor files.

Which is too bad, because I recently upgraded to Alibre Design Expert, which can open and use Inventor files.


The material was a 6" long piece of 4-3/4" diameter 8620 hot roll from eBay. I used a d1-4 back plate from Shars. I think I was into the whole thing for just over 120$

Last questions before I owe you a 6 pack!

1) Where does your fixture and backplate join? I am looking at a few of the photos you've shared of it and can't see a joint.

2) Do you remember your screw spacing?

I built my chuck mount jig like the below, but see that you have an extra set of holes. Just curious why.