Indicating Barrels in a Lathe

[Bob3700]

OK all you gunsmith guru's,

I have fitted two centerfire bbls lately and here is my question. Both gave me similar problems when indicating the bbl into the four jaw chuck.

The bbl work is being done thru the headstock. Muzzle thru the spider indicated in to under .0005". On the chamber end, I began to indicate the bbl in off the lands. I can get three of the lands to read the same runout,.0002"), but the fourth land reads four tenths out.

Now I put a deltronics pin into the bore and can get that to indicate down to two tenths. I put a reamer pilot into the bore and it indicates down to two tenths. Install the indicator on the lands and three indicate down to two tenths and the fourth land is at four tenths.

What am I doing wrong? Why will the bbl indicate in just fine on a deltronics pin or a reamer pilot but not indicate as good when checking off the lands. Also, why do three of the lands indicate just fine but the fourth one is always off?

This has happened twice now, both on cut rifle bbls. Is there an inconsistency in these bbls that I am not aware of?

The muzzle end had 1/4" cut off with a hacksaw so I hoped to remove bbl that was damaged by the centers when polishing.

I have spent a bunch of time trying to get this bbl to indicate under two tenths measured off the lands. It just won't go. The Deltronics pins show that I am at that two tenths now.

Perhaps I am worried about nothing. The piloted reamer is going to follow those lands anyway so I am getting the feeling that I am trying to pick fly shxt out of the pepper!

Your thoughts would be appreciated.

Bob

 

[treeman]

Bob, You may need to take a little more length of of the muzzle. most smiths take at least 1/2"to 1" off before setup.If it indicates ok with an indicator rod i'd say your picking it out of the pepper._______treeman

 

[sjk]

Bob,
Let me start off by saying that not all barrel OD's are concentric to the bore. You'd be surprised if you're checking them down to the .0001's how many show up with a land or groove out of concentricity. A land/groove can be out of tolerance but yet still be in perfect concentricity. Usually though, if you check the chuck or anything round in it, if 3 of the 4 quadrants check out withhout any run out, the 4 th falls right in with the 3. If it doesn't something's wrong somewhere and it may possibly be the part and not the lathe. You mention that you can get it down to .0002. Is this runout or TIR, because run out is determined by the TIR, and then it would be only half of that or .0001. That's pretty close and there's not too much you can do about it if that's the case. Yes there are ways to cure this and machine it "bugs n*ts", but the lathe is the one thing you cannot use accomplish this . This can also be the fault of the manufacturer and he doesn't have the job set up properly all depending on what method he's using for rifling. Just some more .02. Lots of luck in your venture

 

[acloco]

Is it the same jaw,4th) that measures larger each time?

 

[tightneck]

First, I think you should indicate off the grooves, not the lands. I actually look at both the lands and grooves when I indicate, but I use the grooves when adjusting. I pay attention to the lands just to see if they are the same height. I don't think a tenth or two matters too much. Do the grooves show this same .0004" as your indicating, or is it just in the lands? Very simply, one of the lands could be a bit taller or shorter than the others, creating the runout. Also, your spindle may have enough runout in it to cause what you are seeing. As you stated before, a floating holder with the right bushing should take care of this tiny amount of misalignment, but what about when you cut and thread the tenon and shoulder? You want the chamber to run true with the threads and shoulder so its all good when the barrel and action are mated up. I shoot for less than .0002" and get .0001" most of the time. I don't have a clue whether things really need to be this true, but it makes me feel warm and fuzzy inside. For a big game or Varmint rifle, you could probably get away with .001" or maybe even more, but for a BR rifle, I don't want ANY doubt in my head about the rifles' capability. It only takes a couple more minutes to get a barrel to run .0002" once you have it below .001" anyway, so every barrel I do gets the same treatment.

 

[Bob3700]

SJK and Acloco,

First off, I am measuring the chamber end of the bbl as it is chucked in the lathe.

I have the indicator up in the bore and am working on centering the bbl bore with my indicator on the lands of the bbl.,internally).

To eliminate any possibility of the machine being the issue, I rotated the bbl 180 degrees in the chuck and checked the whole set-up again.

Once more, three of the lands will indicate in at .0002" TIR, the fourth land is always .0003"-.0004" TIR.

When I slide the Deltronics pins into the bore at the chamber end, the indicator will show .0002" TIR. With a pilot bushing off the reamer in the bore, chamber end, same .0002" TIR.

Once I get the bbl bore centered, I will turn a register on the outside of the bbl in order to be able to check the bbl alignment without disturbing the setup.

I am getting ready to say that is good enough and rely on the centering based on the Deltronics pins and Pilot bushng TIR.

Bob

 

[acloco]

"Once more, three of the lands will indicate in at .0002" TIR, the fourth land is always .0003"-.0004" TIR."

Is the 4th position always at the same spot on the chuck?

 

[sjk]

Bob,
If you establish that the lathe is not the problem and you do a lot of this work on bbls, invest in a used air gage. They're worth their weight in gold. You can pick up one of the "olde Federals" pretty cheap. Most are graduated in .0001's. You can make up your own inserts for any bore dia you want and get plastic tubing from Lowes. You can tell in an instant if the bore is tapered, wasp waisted, bulged out of round or anything else down the whole length. It will pick up ANY deviation that a slug won't for that particular bore dia. I used this for years and it worked well enough to tell me that ONE bbl maker did the same lousy job constantly

 

[daveosok1]

"I shoot for less than .0002" and get .0001" most of the time. I don't have a clue whether things really need to be this true"

Nope it doesn't. Most of your lathes bearings are far beyond this tight of tolerance and when performing any turning the tool pressure will flex the bearings thats why you can get minute dusting's forever if you choose to continue to spring pass when cutting threads.

The lathe is only as capable of repeating and holding as the bearings are. I can push on our lathe chuck at work and get a .005 thou deflection.

If any of you are using a floating reamer holder then you're wasting your time getting it to within +/-.0002 as the floating holder moves a heck of a lot more than that. Have you even locked down your tailstock and put a dial indicator on it and applied some side force to it, itll move too. The horizontal plane of the tailstock bore is always off every so slightly and almost never inline with the headstock.

Now if you do keep such tight tolerences then you slap a rem 700 mass produced action on it and wasted all that time too.

Even if you trued up the action when you install the bolt the upward pressure of the sear puts the bolt at an angle offsetting the case and presetting it off center. When its fired it all slams back into place and a violent occurrence happens pushing "+/-.0002 out the window. The barrel harmonics, thread engangement, bedding and stock all deform under the pressure and some how factory guns have shot .150's with no custom work done to them the only difference is on a completely custom gun you can't lie your way out of a mis it was you not the gun because in that case as is with most custom guns they outshoot the owner 99% of the time.

I'd consider concentricity, thread engagement, thread tennon torque rating, lapped scope rings, bedding, and lapped bolt lugs to be as inline and as square as possible before attempting to hit +/-.0002, +/-.0015 would be acceptable and even more on a hunting rifle.

Consider this when truing a rem 700 action. Its the story of what came first the chicken or the egg. What do you do first or what should be done first on a rem 700? Square the action or something less common?

Ream the bolt way, install arbor with centering bushings, cylindrical grind the od so that it is perfectly concentric to the id, Place in four jaw chuck square face of receiver and lug abatement, square bolt lugs and true up bolt head and face, bush firing pin hole, bush bolt for a .001 thou fit.

Now you have a concentric action with little to no free play in the bolt to action fit. The bolt and action engage so that both lugs are engaging the bolt lug abatement area and under pressure of firing will not distort to the amount a action that hasn't undergone such methods will. Use Dave Mansons oversize thread tool for fresh threads or chase them on the lathe use plenty of spring passes all taps are ground for 75% thread engagement you can get more by making the tap drill size hole smaller.

Place barrel in four jaw indicate to within +/-.0005. Ensure other end is also inline with the bore so that the bore is running concentric to the lathe. Perform everything else the same as you've always done it and use diamond grit lapping compound in the 1 to 2 micron range to lap the thread engagement. Grind recoil lug to ensure square and parallel surfaces for barrel fitment.

Now factory Rems, Wins and now Savages without all this crap done to them are holding sub MOA groups with handloads and even factory loads. So whats the big deal, well if you do perform all the stuff you can to remove any doubt that its the weapon it then becomes the shooters fault and you can fine tune that too but that takes years not hours.

 

[Clark]

We started out with a 4 jaw and a spider and dialing in both ends in the grooves to within .0001".

Lately, my brother and I have been dialing in the 4 jaw and the spider on the grooves, and the breech is in a Copper gimbal in the 4 jaw. It did no good to dial in the muzzle if the barrel was just bending to conform.

We have been getting .257RAI rifles that will shoot in the 4's.

But we are amateurs and Randy Ketchum is a pro.
He grinds a spud to within .0002", puts it in the breech and dials the spider until there is no run out over a length of the spud.
He says all barrels are bent, and the chamber needs to be concentric with just the local part of the barrel.

 

[ZDH]

What are you using in the headstock for the barrel to float in?
If you are chucking the barrel in the head stock without a "bushing" so to speak, then you are just hurting yourself when you adjust the spider. I use 4 gauge solid copper wire and hammer it around the barrel cutting it off where it doesent toch ends. This helps the barrel float when you adjust the spider. You may be using something already but I didnt notice when I read the thread.

Zach

 

[Clark]

I have been using AWG#10 solid Copper wire to make a gimbal for the barrel in the 4 jaw chuck.

There is some problem getting traction on highly polished Lothar Walther barrels with Copper in the 4 jaw. I have had to rough up the area for traction.