another chambering question

[boltman223]

What I am wondering is, when chambering a barrel is it ok to chuck it up in a four jaw chuck and not use a spider on the rear spindle? I hope this is not to vague of a question as my knowledge of machining and the terms are limited. I know there is other methods (not to familiar with all methods) but this is what is available to me. I have a machinist that is willing to help me and teach me what he can, free of charge.

If you need any clarification please ask.

Any and all suggestions/input will be much appreciated.

 

[X Ring Accuracy]

It is best to support both ends of the barrel and be able to dial both ends in as well. Kinda playing with fire letting the muzzle end find its own path. There are many ways to skin a cat in this regard. Your machinist buddy will help you find a way to get the muzzle running true.

 

[Preacher]

If a barrel is long enough to stick out of both ends, there is no reason not to use a spider.
On the other hand, if the barrel is to short (think 16" XP-100 barrels ) you have no choice but to use the steady rest, or just chuck it in the 4 jaw and get to it.... To me the steady rest is a PITA...

 

[jscandale]

+1 on Preacher's comment.
Nate at Straight Shot Gunsmithing has something called the True Bore Alignment System that is just the cat's meow for this very application. Not a bad price either for what you get.

JS

 

[Lapua40X]

http://www.straightshotgunsmithing.com/

 

[Larryh128]

If the barrel won't go thru the tailstock, you can make a center that holds the muzzle end of the barrel. It still is attached by snugging down the spider. The center needs to be as tight as possible to the tailstock diameter. Mine is made out of turned aluminum with a brass center attached.

 

[eddief]

You could also use an action truing jig to chamber a barrel. This would limit you to the Gordy method though.

Lots of rifle rifles chambered both ways.

 

[boltman223]

Thanks guys.

I talked to my machinist today, he said he has no problem making a spider for thr rear spindle. He seems hesitant to clamp down on the taper though. He mentioned puting it in the check about 4 inches back where it is straiter. He also mentioned doing it on the cnc. He said he wants to think things over and figure out how he wants to do it. Hour this is mot his way of saying he is not intdrested.

I have seen the true bore alignment system, in fact nate just did a rifle for me a few months ago. If I could afford it I would buy one.

 

[hogpatrol]

Any comments on using these methods? Am getting ready to do a 17 and a 20.

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

http://www.youtube.com/watch?v=1d989VrW_70

 

[jscandale]

That is a very effective way of skinning the cat. Bob Pastor's results speak for them self.

JS

 

[Erik Cortina]

The thing that worries me about Bob Pastor's method is how far away from the chuck he chambers. I would be worried about flex on the work piece.

You could do what Bob does, but support the other end of his fixture in the steady rest. That should take care or any flex.

 

[jscandale]

Supporting one end of the fixture would completely defeat the purpose of indicating the center line of the bore. Everything flexes all the time, even in the chuck. I would be more worried about catching malaria on a trip to Alaska in November.

JS

 

[Erik Cortina]

Supporting one end of the fixture would completely defeat the purpose of indicating the center line of the bore. Everything flexes all the time, even in the chuck. I would be more worried about catching malaria on a trip to Alaska in November.

JS

I don't see how it would defeat the purpose of indicating the center line of bore.
You put fixture in chuck, support it in steady rest, then indicate barrel after you have it supported, not before.

 

[jscandale]

Not saying that it's not entirely possible, but I'd like to a video of the process of trying indicate off the OD and the ID of something in the same rotation. I think it would an "R" rated video.

JS

 

[jscandale]

Erik,

Question: How would you ensure that the center line of the fixture is spinning true prior to inserting the barrel in order to indicate that? If you just indicate the OD on both ends or the ID of one end, it seems to me that it would be very difficult to be sure that the axis of the spindle is spinning on the exact same axis of the fixture if it is being supported from the OD. Then, how would you control the inevitable flex o the fixture once the bolts are snugged up on the work inside the fixture?
I realize how impractical my questions is, but it's a good exercise to keep the brain active. How you don't mind.

JS

 

[Erik Cortina]

I think you are over thinking it.
Set up the fixture in 4 jaw and steady rest (it doesn't have to be indicated perfect, just close). Then insert the barrel and indicate barrel using the 8 fixture bolts to indicate it perfectly. The barrel will be running perfectly true even of the fixture is not.

 

[jscandale]

I would respectfully, but strongly disagree. If you are going to support the fixture at both ends on the OD, it would have to be absolutely perfect, or the result would be the fixture acting as a ball joint in the chuck, constantly readjusting to meet the pressures that the steady rest would impose. Now you would introducing even greater pressures on the fixture than if the steady rest were never introduced into the equation.

JS

 

[Erik Cortina]

I would respectfully, but strongly disagree. If you are going to support the fixture at both ends on the OD, it would have to be absolutely perfect, or the result would be the fixture acting as a ball joint in the chuck, constantly readjusting to meet the pressures that the steady rest would impose. Now you would introducing even greater pressures on the fixture than if the steady rest were never introduced into the equation.

JS

Then indicate fixture in 4 jaw and steady rest, then indicate barrel inside of fixture. It would be more rigid.

 

[hogpatrol]

I think you are over thinking it.
Set up the fixture in 4 jaw and steady rest (it doesn't have to be indicated perfect, just close). Then insert the barrel and indicate barrel using the 8 fixture bolts to indicate it perfectly. The barrel will be running perfectly true even of the fixture is not.

That fixture isn't hanging out far enough to warrant a steady rest. In addition, a steady rest introduces another variable in the setup, i.e. you are using something that can wear while in contact with the fixture, either the fixture (aluminum) or the steady rest pads.

 

[jscandale]

Erik,

I agree about the rigidity to some degree, but I debate the concentricity of multiple axes and the considerable opposing pressures of one end of the fixture vs. the other.

JS