Truing a barrel.
I’ve been reading up on this. The general tactic seems to be to establish how far out of true the bore is to the OD and then use a four-jaw chuck to accomodate the mis-alignment. Which is fine for the job at hand, but one is still left with a barrel that has it’s bore out of line once the barrel is bushed and mounted in the frame.
So I propose to make a .25 cal push-fit brass insert for the chuck-end and use a live centre at the other end, so that the barrel revolves true to it’s bore, and then turn the OD the full length of the barrel ( a bit will be missed, due to the constraints of the cutter, but I’ll lop that bit off).
In such a case, by how much might I expect the centre of the barrel to flex, given a starting OD of 15.5mm? I have a follow-rest, but I don’t like using the gouging POS. If I take very light cuts (like 0.10mm) will there be any meaningful flex at all? Overall barrel length is 23.5″ which I can fit onto my lathe with about an inch to spare.
All Replies
4-jaws are great for what they are intended. They cannot replace a 3-jaw as they are limited on spin speed. So just because you mount a 4-jaw all is not ‘best’
A 3-jaw cannot do what a 4-jaw can. flexible holding and accurate alignment. Few of us will be able to afford the class of machine or chuck that Walt in Hw is speaking of.
Lang, it is a skill worth learning no matter how much you get fits from it
Any added skill wrt machining is worth the effort for sure.
The way I do it is center the breech in the center and reduce the diameter as applicable so breech runs concentric to the bore.
Mount bushings with a fairly heavy press fit, mount up barrel and reduce oversize bushings to size which makes the bore and bushings concentric.
Done, easy peazy…..
Walter….
I should also mention theres a big difference between the rough industrial machines that i’m used to working with & gunsmithing. 90% of the pieces I have to mate to are usualy held to a +/- .0025″ tolerance so for me to spend extra time fiddling with .0001″ accuracy would be wasted effort.
walt
Wow, I’d like to use your lathe! .0002″ is better than most collets. My 10″ 3-jaw would make you puke, addmittedly it’s not the best quality chuck but I have to make do with what the budget allows. I almost always use the 4-jaw round or not. It grips better and I can set things up to run as true as the job calls for in short time after practicing with it. I don’t use two keys either. The only time I really go for the 3-jaw is when turning hex stock.
c’mon lang. Get with it. Machine setups have to be undertaken and then broken down. No way around it, I’m afraid. But running from it won’t help you. One tip; I have a really thick, about 1″ piece of tough marine plyboard that I cover the ways with whenever I am changing chucks… just in case it slips. It will nick the ways and you don’t want a nick that close to the headstock, it’s where the meat of your work will be done. My 6 jaw chuck weighs around 60 lbs, and my 10″ 4 jaw probably a bit more. They are a pain to change, but you put up with it because that is the nature of a lathe.
Watched the vid and I’m not sure how well that guy is chucking his 4 jaw setup… 2 keys are nice, but not necessary. Besides, you almost never chuck round stock in a 4 jaw, it’s never that easy. Normally its something eccentric. I’ve used 4 jaws to chuck whole actions when I didn’t want to remove the barrel from the receiver just to recrown. Stick the whole thing in there and spin it up, run the barrel into a steady. Frequently you must shim the jaws with aluminum to keep them from scratching the surface of your gun, which makes them hold a bit less securely. Just cut shims of alum into a squared off C shape and fold them over your jaws. Start with slower speeds, watch the off center weight and be sure it doesn’t get so severe it tosses your work.
If my 3 jaw ran off by .002 or .003 thousandths I’d have tossed the lathe into a ditch years ago. You guys are nuts if I’ll work with that kind of tolerance. Should be .0002 and you’d be in the right ballpark. Order of magnitude. Unturned stock is frequently off by .002 or .003 or even a bit more (both solid bar and tube stock); is that what you were referencing? But certainly not the chuck. Now, the ability of the 3 jaw to accurately rechuck something once you take it out… now that is an art and ‘feel’ that is acquired.
walt
Tell me about it. My lathe has a 12″ 4-jaw that weighs about 80 lbs. Too light to mess with a crane, but too heavy to want to do it by hand.
Have fun.
Probably wouldn’t notice too much difference but I have a habit of trying to get things perfect lol.
I’m not trying to bust your balls but I don’t see the advantage of using the 3-jaw that will introduce unncessary runout when a center would be easier with next to none.
Either way 1/16″ is alot.
I guess the main advantage is not having to dis-mount the 3-jaw and mount the 4-jaw. 😆
And if I can get the barrel to where I can see no wobble with the naked eye, that’ll be a vast improvement on an un-turned item. I do consider myself a perfectionist, but also consider too much perfectionism to be a disease I’ve got fairly well under control in my older age.
Probably wouldn’t notice too much difference but I have a habit of trying to get things perfect lol.
I’m not trying to bust your balls but I don’t see the advantage of using the 3-jaw that will introduce unncessary runout when a center would be easier with next to none.
Either way 1/16″ is alot.
Two to three thou? I can live with that. The guy showing how to set up the 4-jaw was down to half a thou…is it worth all that extra effort for the sake of one and a half to two and a half thou? I believe the test-report that came with my lathe shows it being precise to a +/- of 2 thou on it’s various moving parts.
Bearing in mind that when I span up my .22 barrel it was out by as much as a 16th of an inch. If I can reduce that to 3 thou I’ll be more than satisfied. 😀
.002-.003″ When new for a quality chuck, more for bargain brands. They get worse as they get older and the bad part is you will never be able to indicate in the exact same way twice.
That was highly informative, thanks. 🙂
How far out can a 3-jaw be? 😕
4 Jaw Chuck Demo
Did you indicate the bushing on the tailstock chuck? Check it before you go cutting on your barrel!
With a 3-jaw I don’t see how you will end up with zero runout. With a dead center you will have zero and with a quality live center you will be down in the .0002″ T.I.R. range.
Maybe I am not seeing something here? I’d think a 4-jaw on the headstock end with the tight fitting bushing and a live center in the tailstock would be the easiest way to turn the whole barrel in one pass.
You should tackle the 4-jaw, it’s not that hard for what you are trying to do; it only gets fun when trying to set up to turn eccentrics.
Good luck & take care,
walt
I hear ya Walt. 🙂 But progress is also made by people who buck the trend and try new ideas. Most crash and burn of course but occasionally one makes it through. I’ll have a fire-extinguisher handy. 😆
Ok mate, will do.
- You must be logged in to reply to this topic.
Not sure if it’s relavent Lang but i tried to machine a piece of seamless stainless tube. Only wanted a machined finish on it, but as i got further down with the cut it got progressivly more bent (from being straight to start with).
I wasn’t trying to true it up in any way just put a cosmetic machined finish on it.
When i”d finished it’d visibly bent by three or four mm.
This i’m told was due to the sterss in the steel.
Not sure if you’ll encounter anything similair but i bet ther’ll be a certain amount of stress in the barrrel to start with.
And what walt said.