Dilaing in setbacks

Butch Lambert said:
You're wrong Jerry. I'm boring to the point in the grooves that I indicated. If it wanders beyond that point and the bushing follows it your chamber will be a larger diameter at the base.
Butch
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Think about it Butch. If your chamber comes out larger in the rear it is not because the little slim pilot nose is pushing the entire reamer off. The tail does not wag the dog!!

Edit- There is an old machine shop saying that "carbide does not bend". Well, nearly doesn't bend. So, if you were using a carbide reamer in a big bore cartridge, like a 416 Remington or such, then I would agree that a wandering bore at the reamer nose might oscillate the reamer base enough to create an oversize chamber base. But, something like a 6mm PPC, I would bet against it!!

If you have significant bore wandering where the pilot runs, or if you are getting oversize chamber bases, I;d recommend relooking your chambering process.
 
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OK Jerry,
In all of your infinite wisdom, tell me how you would straighten the rifle bore? If it wanders off a setup up ain't going to straighten the bore.
I don't have that problem, but would by letting the bushing wonder down a yawing bore.
Butch
 
Butch Lambert said:
OK Jerry,
In all of your infinite wisdom, tell me how you would straighten the rifle bore?
Butch
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Remember what the spy said, "if I told you I'd have to kill you"!!

I think you are over imagining how a bore curves. Probably 0.015" at the VERY most from a really bad barrel.

What we are trying to do is to not over correct for that wandering, just get the leade/freebore to merge symmetrically with the bore at that point.

Remember, we are dealing with concentricity error not cylindricity error.

http://www.emachineshop.com/machine-shop/Cylindricity/page606.html

http://www.emachineshop.com/machine-shop/Concentricity/page618.html
 
JerrySharrett said:
What we are trying to do is to not over correct for that wandering, just get the leade/freebore to merge symmetrically with the bore at that point.

Remember, we are dealing with concentricity error not cylindricity error.

Jerry,

It seems to me that what Butch is saying is exactly "concentricity," using median points at the neck and the leade. What you seem to be advocating is to achieve zero "runout" at the reamer bushing that is chasing the wandering bore. http://www.emachineshop.com/machine-shop/Runout/page607.html

I don't think either of these methods deal with "cylindricity."

Hope I don't get run over by a truck,
Jim
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I think we all can agree what we are after is the throat of the chamber to be as close to dead center of the bore/groove/hole as possible. We pick that particular place, and work to it. Granted, most barrels aren't terribly crooked (hole drill drifting) but it can happen.

We also have to set up a barrel, run the indicator in there, and decide what we will reference off of. I've seen the tops of lands that have some slants to them, lands that vary a little in their height, and even grooves that aren't exactly consistent in the arc they should be. So you decide on what will be the best thing to work to. You can only do so much. I guarantee either way being talked about here will produce a fine shooting barrel, if the barrel wants to shoot!
 
Jerry,
You straighten the bore by drilling and taper boring to the indicated leade-freebore. It will be straight to that point. What the bore does after that we have no control over.
Butch
 
Boys, boys, boys,,,,

Jerry and Butch, I love and respect both of you like my own brothers and would not do or say anything that might hurt your feelings, but sometimes we have to step in and separate you before things get out of hand. So consider it done and let's move on. :D

When it comes to dialing in barrels to two tenths etc., I am reminded of an old saying often heard concerning aircraft performance data. It goes something like this;,

"You measure it with a micrometer, mark it with a grease pencil and cut it with an ax!" :p :rolleyes:

And so it is with this chambering business. Whether you work thru the headstock or in the steady rest, you can measure much closer than you can cut. Regardless of how close we dial it in, I'll bet the chamber winds up in exactly the same place anyway. :rolleyes: What do ya' bet? :p

These little lathes we use are not capable of directing a reamer to the nearest tenth down a rifle barrel; it's gonna' go where it wants to go regardless. :rolleyes: Try this,, Extend the tailstock quill out about where you usually have it when chambering and place a dial indicator on it. Now push on the center with your finger. It moves back and forth a surprising amount ala floating reamer holder. I'll bet even Jackie's big Pratt and Whitney deflects a bit.

Later

Gene Beggs
 
Gene,
What difference does it make even if the tailstock is made of rubber? Jerry is going to buy me a drink at the Super Shoot, right Jerry?
Butch
 
Butch Lambert said:
Gene,
What difference does it make even if the tailstock is made of rubber? Jerry is going to buy me a drink at the Super Shoot, right Jerry?

Butch
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You got it Butch. You know where I'll be, come by any time.

I see Snyder deleted his post about feeling Buch's pain. I was trying my best to be his pain!!

I even thought for a while that I was going to have to baffle PawPaw with BRILLIANCE to get my points across.

Gene, you come by for a drink too. If I get Butch drunk enough he'll admit the truth that I've been right all along!!

As to measuring closer than I can cut, not so. When I cut it is an exact dimension but it does not always measure that way.

I like Ross Perot's way, measure twice, cut once.
 
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