Short Barrel Chambering Fixture

[epanzella]

I had put this in another thread but thought it would be better here. I'm starting a short barreled smokeless muzzle loader build that won't reach my outboard spider. My son had a 4 inch hunk of solid 6061 laying around so I decided to build a fixture like I've seen elsewhere on line. I have 3 rows of holes. The first 2 rows are 2 1/2 inches apart for bolt work and barrel stubbing. The first and last rows of holes are 7 inches apart for holding rifle barrels. My outboard spider on my Grizzly G4003G requires at least a 22 inch barrel length or it can't be used. As this is going to be a stub job, I also needed a fixture that would allow me to dial in something only 3 inches long. The bolts are made from allthread 1/2 x 20 rod. The bolt heads are nuts TIG'd on and the brass tips are pressed in. I love 20 pitch because each complete turn is .050 inches.

 

[derf]

So how do you set it up to chamber? Looks like a nightmare to indicate.

 

[epanzella]

So how do you set it up to chamber? Looks like a nightmare to indicate.

You indicate it the same way you would if you used the outboard spider and a 4 jaw. The bolts are all at 90 degree increments and lined up with each other. You don't use all 3 rows of bolts at the same time, you just pick any 2. For a rifle chamber you would use the front rom and the last row, essentially giving you a pair of 4 jaw chucks 7 inches apart. For a barrel stub I use the first 2 rows that are 2 1/2 inches apart. I don't have any long reach TI's so I use a long piece of music wire in a toolholder and indicate that. By running the carriage back and forth I can check the piece at any depth without changing the setup.

 

[killswitch505]

Nice!!!!! I wish I would have built mine I have the viper similar to what you built. I mounted a bald eagle spider to a face plate I can do a 20” barrel through the headstock of mine now

 

[epanzella]

Nice!!!!! I wish I would have built mine I have the viper similar to what you built. I mounted a bald eagle spider to a face plate I can do a 20” barrel through the headstock of mine now

I always wanted to speak to someone with a Viper! On your unit the flats for the 4 jaw line up with the brass tipped bolts. I always wondered what the reason for that was. On mine I put the flats for the 4 jaw in between the rows of bolts to give me a bit wider span. In use I have to reach in between the jaws to adjust the last row of bolts. So far I don't see a problem but since i recently completed mine I haven't used it much. Do you see any downside to the way I built mine?

 

[Tozguy]

Very good work epanzella. I'm betting that it will work out fine.

so I use a long piece of music wire in a toolholder and indicate that.

Would you elaborate on how the music wire is used to indicate at depth please. I have an idea but would like to be sure.
Thanks

 

[epanzella]

Very good work epanzella. I'm betting that it will work out fine.

Would you elaborate on how the music wire is used to indicate at depth please. I have an idea but would like to be sure.
Thanks

Sorry I wasn't clear. The music wire is not indicating depth but concentricity. I'm trying to emulate a long reach test indicator. On the stub job I need to bore out a 3 inch piece of barrel and thread it for the tenon I'll machine onto the new barrel blank. The barrel piece contains the 12 gauge chamber which is tapered so I have to indicate it in 2 places to insure it's aligned with the barrel centerline. It's similar to indicating in a whole barrel for chambering but it's only 3 inches long. I put a piece of 3/16 music wire in a tool holder and run the carriage down until the end is in the chamber. I turn the xfeed until its rubbing the side of the chamber. Now as the fixture turns the music wire will oscillate with any runout in the chamber. I indicate the wire between where it exits the barrel and the tool holder. The mag base is on the xslide so I can sweep the chamber with the carriage handwheel without disturbing the setup. I just keep going back and forth indicating one end then the other end of the chamber until it's dead nutz concentric.

 

[Tozguy]

Got it, thanks for the explanation.

 

[epanzella]

Just a followup. It's been 2 weeks since my knee replacement and I'm able to hobble into the shop for brief periods. Here are some pix of dialing my stub barrel into my chambering fixture.