turning thin shotgun barrels???

[jerrywh]

HOW BEST TO--- turn thin walled shotgun barrels.  Like the early french barrels .040 wall thickness at muzzle.

[44-henry]

Sounds like a good job for a close fitting mandrel held between centers, I suppose you could sweat it on near the ends.

[keweenaw]

Jerry,

I don't think they were turned that thin but rather the general profile was set along with general thickness when the damascus was forge welded.  If turning was done it was to some reasonable thickness and then the barrel was final profiled profiled and thinned by filing or grinding on a large wheel.  English shotgun barrels are still made that way with wall thickness down into the .025" range.

I  turned one pretty thin by working in short segments with the tool work all done between two steady rests, taking very light cuts. It helps a lot if you have a lathe with a sufficiently long bed to do all the work between centers - I had to work at night on someone else's lathe to get the long bed and pair of steady rests. I cut the tapered sections using the taper attachment.  Used 5 different tapers to get the swamped profile I wanted.  Think it took 7 hours of lathe time for a 36" barrel that started out at 1 1/4" straight.

One could use a follower rest (but not with a taper) but if the barrel developed chatter you would be screwed.  Of course the bore  needs to be perfectly straight.

Tom

[Jerry V Lape]

Jerrywh, I know you like challenges but my suggestion in this instance would be to buy the barrel from a custom barrel maker like Getz or Rayl who are already setup to do such work and experienced at it.  .040 isn't all that thin in terms of shotgun barrels.  .025 -.030 is fairly normal for muzzle wall thicknesses and there are guns in use which have been thinned to .020 or even .018.  Thickness at the muzzle is mostly to have sufficient strength to limit denting from minor bumps.  I am sure you are aware the first 9" or 12"  of a modern shotgun barrel bteech end must be considerably thicker but near the muzzle the pressures are pretty low.   

[jerrywh]

Getz can't  meet my schedule. Neither can Rayl. Rayl won't stick to my specs either . He's afraid of liability. I have long hammock working on it but might have to do it myself.  I was thinking of putting them between centers and filling them with cerosafe to stiffen them. My lathe has sufficient distance between centers. 

[Robby]

There is a tool attachment you could mount on your lathe to bring the barrel to your final dimension. I tried to find it on the computer but have little skill in this realm. It is an air actuated oscillating, honer, used in making and finishing the exterior of the working rods in hydraulic machinery, like backhoes. It is a fairly small simple machine that can be mounted on the compound of a lathe. It uses different grit stones, course to fine, even steel can be finished to the point that it looks chrome plated. Hope this info is of some use.
    Robby

[Evil Monkey]

Jerry, two thoughts, if the outside contour is exactly what you want and you just want ti thin the walls, I think the easiest, fastest and safest would be to ream the bores out until the desired wall thickness is reached. If, in addition to thinning the walls you also want to change the profile and/or want the barrels to have smaller outside dimensions, I would consider draw filing them.

[jerrywh]

If the French and the Belgians did this 100 years ago and more, It can't be that hard , Right?? 
They made these barrels with .030 walls in the 1700's it must be done on a lathe otr a grinder.

[oldiemkr]

I've been thinking about this. I've been a machinist,die maker and instrument maker for over 40 years.

I would not try to turn your barrel. My experience with turning thin wall tubular stock and a couple of barrels has been less than satisfying.

Your barrel was probably hammered into shape over a mandrell or extruded or a combination of both. I'd be willing to bet the ID is not concentric with the OD and the ID you would be turning is not exactly "round".

The pressure of a single point tool taking away a few thousandths or material is too much to keep the material from tearing as you cut it.

You might be able to  cut the barrel in increments only one or two inches long but then you would have quite a polishing job to smooth out the length. I don't know how much lathe experince you have but do not try to make one long cut on material this thin. It will tear.

If the barrel is damascus, well thats another story. I would not try it either.

[Metalshaper]

Gang,

  Asking this to maybe?? assist Jerry and to educate myself a bit more.  But couldn't the barrel be set up on a lathe and then, if one is available?  a tool post grinder be used to thin the barrel down?

I know these grinders can be fit with different grit wheels. Couldn't one be set it up with a fine cut wheel, Then using the cross feed, the material taken away in very small increments??   and also depending on the wheel, it would leave very lil finish work??

How about it ?  am I way off here,, or is this a possibility?

Respect Always
Metalshaper

[Brian]

I know very little about intricate lathe work, but I was thinking along the same lines as Metalshaper.  A very, very fine abrasive wheel mounted on a post grinder that could be worked along the length of the barrel.  You could grind off cuts so fine you could hardly hear the wheel touching the barrel.  That should keep the barrel from flexing, and the finish would be quite smooth.  It would take a while - but I don't see why that would not work.

On the other hand, I admit I know very little about lathe work, especially fancy work like this.  Most of you guys have forgotten more about this kind of thing than I'll ever know.

[jerrywh]

I think I have this figured out but keep on with the suggestions. all is appreciated.

[Metalshaper]

Jerry,

 Let us know how you end up doing it!! 

never know when the same thing may be needed, at a later time?

Respect Always
Metalshaper

[Jim Filipski]

If the French and the Belgians did this 100 years ago and more, It can't be that hard , Right?? 
They made these barrels with .030 walls in the 1700's it must be done on a lathe otr a grinder.

Jerry would they be using steel in the barrels in those times, or iron? I would feel much better with iron barrels.
Jim

[Acer Saccharum]

Jerry,
Most barrels I have turned, I've screwed up. Sometimes I think this is because the barrel steel was stressed, and I should have annealed the metal before turning.

The first time I turned a barrel, I turned and turned until it looked pretty good. Polished it all up nice, etc. When I looked through the bore, the bore was curved so bad, I could not see through, only saw light.

Now I think I would make sure the bore was straight to begin with, then turn some locations 8 or ten inches apart for a steady rest to ride on. If I was to do a real thin wall barrel, I would turn a mandrel or fill the bore with Cerro, as you suggested.

[albert]

If you would go with the grinding approach,you would want an open - grain mediem to coarse grit wheel that won't load up too bad,and use a flush coolant.I have ground quite a lot of steel parts on a cylindrical grinder where I work at,and sometimes the part will get a vibration going which cause problems,but normally can be overcome by how you dress the wheel, and what grade of wheel you have.

[jerrywh]

That is a good idea about turning a section in the middle for a steady rest. My latest idea is to turn the thin end first. I will make a big split sleeve about 1/2" thick and about 11" long.  After turning about 12" of the thin end , which is straight, clamp the sleeve on the thin end and then turn the next 12" or so.
  My theory is this. The barrel vibrates because it is thin and flexible but the sleeve should have the same effect as if the tube was thick. It should stop the tube from flexing. I might have to fill the tube with cerro safe or put a mandrel inside to stop it from collapsing. It will need a mandrel at the end anyway, so as not to flare the end. After that the thin end can be placed in the chuck to do the thick end.  What do you all think???
 PS. I don't want to spend $2000 for a tool post grinder that might not work.

[davec2]

Jerry,

Fill the bore with cerro bend or cerro safe to dampen any vibration.  The tool post grinder is the best way of removing material without messing up the barrel.  I didn't want to spend a lot of money on a commercially made tool post grinder either.  I made one up from an inexpensive die grinder (the kind you can get for $40 from Harbor Freight).  I made a split clamp block from scrap aluminum (but have also used maple) that holds the grinder on the tool post.  You can use a course grinding wheel on an arbor that fits  the die grinder chuck to remove most of the material and then switch over to a finer wheel to get a better finish.  I also run the lathe backwards so that the grinding wheel and work piece are counter rotating - better finish, less vibration, and faster material removal.

[Dphariss]

That is a good idea about turning a section in the middle for a steady rest. My latest idea is to turn the thin end first. I will make a big split sleeve about 1/2" thick and about 11" long.  After turning about 12" of the thin end , which is straight, clamp the sleeve on the thin end and then turn the next 12" or so.
  My theory is this. The barrel vibrates because it is thin and flexible but the sleeve should have the same effect as if the tube was thick. It should stop the tube from flexing. I might have to fill the tube with cerro safe or put a mandrel inside to stop it from collapsing. It will need a mandrel at the end anyway, so as not to flare the end. After that the thin end can be placed in the chuck to do the thick end.  What do you all think???
 PS. I don't want to spend $2000 for a tool post grinder that might not work.

Follow rest will work but it would require care not to "roll" the barrel to a smaller caliber.

You could use a belt sander and make a holder that allows the barrel to spin freely. But this is not terribly precise and would require a wide belt and practice.

I would not use a grinder on my lathe...

Dan

[keweenaw]

Jerry,

You can borrow my tool post grinder if you pay the shipping and put on a new drive belt.  You'll probably have to buy some new wheels and will, of course have to make a plate to fit whatever slot is in your compound rest.  As Dave said, you need to run the lathe backwards. You'll need a flush coolant as otherwise the barrel will get longer and bend.  If you do want to turn off some of the metal, working between two steady rests if the way to go. 

Tom

[Acer Saccharum]

What about getting a split shaft collar, boring it to fit the barrel, and then turning the OD of the collar smooth to run in the steady rest.

[Dphariss]

You could also set it up in a lathe and use a long angle lathe file and simply file it down to size.
Probably the safest way. No grit in the lathe ways etc. little heat or pressure.

Dan

[44-henry]

If you are looking for a tool post grinder www.littlemachineshop.com has some designed for the 7-9" lates for about $100.00 which are good values, you probably would need to modify them slightly to fit your lathe, but they can be handy to have around. I've used the one we have in our lab on our 15" lathe with some modification.

[flintsteel]

I guess you can try to reinvent the wheel but why not just do this the way it has been done for four or five centuries: place the barrel in a lathe and about every six inches make a small guide cut to indicate the thickness desired at that location.  Then remove the barrel, place it in your vice or a jig and with a hand file taper the barrel.  I guess tens of millions of barrels have been made this way and it has worked very well.  Try it.....

[jerrywh]

Flintsteel.
   Where did you get that information??