contouring a new blank

S

skeetlee

Active member
If i were to re-contour a new barrel blank will it induce stress into that barrel? What i am curious about doing is taking a half worn out LV 6ppc barrel and turning it down closer to a rem varmint contour. Will it mess it up? Lee
 
Whats up wayne? We have a taper attachment for the lathe. I dont know squat about it, but we do have one. Lee
 
Awhile back I turned down a Krieger 1.250 straight barrel for my son's AR-15. There's a reason that the German's step contoured their barrels on the 98 Mauser's which is basically what you do for an AR. If you are going to taper turn a barrel it helps to have a follow rest with floating tips with adjustable pressure and a taper attachment. As Wayne said, it won't be fun even then. For a short PPC barrel that has quite a few rounds through it, I personally wouldn't mess with it. I'd just get a new barrel in the contour you want. You're out the cost of the new barrel, but if the barrel is going on something else then you'll probably have to rethread and rechamber anyway. I'd do it on a new barrel instead of rechambering. But, if you have plenty of time, go for it as all you're out is labor and machine time. Being a short barrel is a plus on turning down a barrel. Chatter will be the problem you run into with turning the barrel down.
 
Lee, probably the only way to answer this question is to do it. You will get as many answers "no" as you will "yes". It also is not economical th have it done but since you have a lathe, just have fun. If it works, great, if not, o well. My brother did recountour a 1.25" straight to a taper and it shot well. But that is a sample of one.

joe
 
since you have a lathe with a taper attachment...call it a learning experience and just do it.
if it does not shoot no big deal, you got more lathe time in...

mike in co
 
I don't know about inducing stress into the metal but you can warp a barrel if not careful, I watched a old long time gun smith here in town turn a new 6.5 barrel into a banana. He had it locked up between centers and was using no coolant apparently the barrel expanded an bent the thing. Until I got a lathe with a coolant pump on it I was careful to release the pressure on the tail stock every so often. If you have access to the Gun Smith Kinks books it shows how Ackley ground his bits to tapper barrels thats a good start. You definitely don't want a rounded bit it needs to have very sharp point or it will chatter. I have also used a threading bit with a slow feed rate with good results. The late Jerry Wills from Denver told me that if the barrel is to be tapered you can lock up the breach end in a 3 jaw chuck and then force the muzzle over with the tail stock. I tried it once and it worked great I was just a bit concerned about the light weight lathe I was using at the time and I haven't had a chance to try it again on my new lathe. The thing is some barrels will chatter and some wont I built a fallow rest of sorts that has 3 brass contacts that are spring loaded to hold pressure on the barrel, it works OK its just a bit slow. I have turned a lot of barrels down and cant ever remember one not shooting after I got it on the action....Go for it, if I can help let me know.

Bob
 
Don't the barrel makers grind the profile? If not, why not? I can see roughing it in and then grinding it with a tool post grinder and flood with coolant.--Mike
 
Turned at slow rpm's and a light cut, no coolant - will not warp a barrel that is properly stress relieved. I have turned hundreds of blanks over the years. Only those with poor heat treatment gave a problem.... and that was back in 1968.

I did mine with no taper attachment between centers with an offset tail stock live center. Takes a long time...
 
You can also step turn the barrel and then draw file it to a smooth countour. As said above; lots of work.
 
We will come up with something. Just trying to get the most out of these ppc barrels. Once they come off the target guns, i thought they might make good coyote barrels. They are just a bit heavy, thus the tapering question. I was also under the impression that turning a barrel would cause or induce stress and that it would ruin a barrel. Gun range talk!! Thanks fellas, This is very interesting to me. Lee
 
more like to relief stress........some claim that removing metal can cause the bore to open....

consider slugging the bore at both ends before and after, and report if you can see a diff...

mike in co
 
I have turned two 1.25" x 19" Anschutz bbl blanks down to rimfire straight cylinder contours. There is no more miserable job imo. The only way to do it without a bunch of chatter was to turn them fast and take a heavy cut. Yes they get HOT. I also turned a 26" 1.2" Green Mountain blank . UGH again. One problem is that as you get it skinnier it's more prone to chatter. The longer they are, more chatter. I have one more of the Annie blanks that I am going to fit to a dedicated AR15 upper and that's it, no more miserable jobs on the machines.
 
OK, as to "how" :)

I would ditch the taper attachment for now.

Figure on cutting .005 initially and sharpen your bit with some undercut so's it'll 'pull' instead of pushing the barrel away. A deep chip breaker groove works OK but a vertical toolholder makes it easier.

Now comes the tricky part. Take a magic marker and mark the barrel in increments that match the taper wanted to the .005 cuts And as your carriage runs across just dial in another .005 at each step.

When you're done you can wipe out the .005 steps by hand. It's no harder than blending pitches with a mag.

Or file them out.

al
 
See, I told you....

What I've done once or twice (until I learned it aint worth it) was use the compound. I set the compound to the taper, if I recall it was something like .007" per inch, and "choked" up on the barrel in the headstock. I set the muzzle in the live center and had only a 3rd or so of the barrel sticking out from the chuck. I only turned the 3" or so of travel the compound has starting at the muzzle, then worked on the next 3". Then I only let out enough barrel for another 3" pass, keeping my work as close to the chuck as possible, keeps the chatter down. There is a bit of error when you pick up the last pass, but that isn't too hard to fix once it's all done. Takes a lot of time.
 
I turn betwen centers with the tail stock offset. I use an old welders leather glove filled with brass swarf, weighs about 10lbs, I use insert cutters with a fairly wide radius and a "New-Lube" Micro drip coolant system. I offset so tailstock is closer to me. I match cutting feeds with the what the barrel feels like. The glove (my third Hand) is used to dampen the chatter and rides on the tool post with 1 finger on the front of the barrel and most of the weight on the top back side. I usually turn at 655RPM and feed at about 0.007 IPR. If I used HSS I would have to cut slower to get a good finish. This is the system that is working for me now. The New-Lube System has really made a difference in how my barrels look, cut and the life of my inserts.

Lowell
 
Since it is a cut barreled Krieger, the bore thing is a non issue.

The trick is slow speeds, and a sharp positive rake tool with zero nose radius. Don't take more than .050 off diameter at a time.

By slow speed, I mean the speed at just below the chatter point. It will be worse toward the middle, so you can start fast, and slow it down as it gets to the center, then speed up again as it approaches the chuck.

I have turned Kriegers, and it does not seem to affect them. As for the stress thing, they did not 'warp', so I doubt it added any. If a piece of steel is properly stress relieved, you generally do not have trouble. The reason steel will start to run out after cutting is you are releasing stress in a piece that is not properly stressed relieved.
........jackie
 
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I haven't turned many but the easiest way for me is to set the taper.
Chuck the barrel with about 10" sticking out from the chuck.
This will let me cut 8" of the barrel length. Slide the barrel out another 8". Do it again, done.
If you are carefull at the transitions, sanding will finish it. I cut the small end first.
It will suit me if I never have to do another. Kenny
 
I do mine in a CNC using coolant and only the finish tool. I'd recommend coolant if you can. The lathe is 15" between centers (thereabouts) and it works wonderfully. I begin by doing 1/2 of the barrel, then I make a 1.5-2" alum tube that fits the barrel taper I just cut. This is OD turned, then ID bored to fit. It snaps on like a morse taper, then I turn the barrel around, chuck on the alum, and do the other half. With your taper attachment, you can do the same thing. The fit of that tube does have to be reasonably close. Make sure you put good centers in the barrel before beginning. Obviously, I use a live center in the unsupported (not in the chuck) end. I also use that tube trick for any crown work.

The inserts I use are a 135 Deg standard finishing insert, with a .015 radius iirc. With careful indicating on the part, you should be able to have a transition that cleans up with a file, and after sanding the barrel, is invisible, even when looking right down outside of the barrel in the sunlight. With the barrel chucked, and only 1/2 of it being worked at one time, chatter is a non issue. Well, it has been so for me anyway.

And no, you won't hurt the barrel one bit. The barrel maker turned it to begin with. If it ain't crooked now, it won't be when you're done, unless you get it hot as blazes when doing crappy turning work. Mine make real nice, tiny gray chips when I do them. I would guess I did about .050 or so per side depth of cut. Feed was whatever the lathe chose, and rpms were not very high. Probably in the neighborhood of 200 or so. The feed was enough to break the chips nicely, and get the heat out in them.
 
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skeetlee said:
If i were to re-contour a new barrel blank will it induce stress into that barrel? What i am curious about doing is taking a half worn out LV 6ppc barrel and turning it down closer to a rem varmint contour. Will it mess it up? Lee
Click to expand...

In 2005 when I was spending a lot of effort on barrel tuners many barrels had to be turned to reduce weight to accommodate the tuners. I turned at least 8 barrels without ill effect to the bore. All the barrels were slugged before and after turning, no detectable change. During this exercise I turned Hart, Krieger, Shilen and Spencer barrels. All, I'm sure, had different heat treating during manufacture and there were cut and button riflings in the mix.

Turning rifle barrels is not easy though since they are long and limber. Chatter will be the biggest problem. Like written above, use a very sharp cutting tool with near zero nose radius. Most carbide inserts made for production will not work.

Having a variable speed spindle helps keep chatter down. I have a VFD on my South Bend and that allows speed changing on the fly.
 
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