machining long bore
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  1. #1
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    a guy has asked to me machine a long bore(20" long) 3/4 diam for a barrel sleeve on a rifle...what would you need for tooling to do such a job?...ive never done this deep of a bore before...obviously a long drill to start?...lots of peck drilling to remove the chips?...then?

  2. #2
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    Gun drill it...
    Jim

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    Quite a challenging job [img]smile.gif[/img] How much material is left after you've put that hole in it?

    I think I'd be sweating bullets thinking about installing the new sleeve in it. Anyone make a 24" long taper reamer?

  4. #4
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    im not familiar with gun drills...it actually fits on the outside of the barrel...i believe it is 13/16" od...it is stepped inside...3/4" for a distance and then 11/16..

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    Depends a bit on the tolerance. Gun drilling would be nice but if you can't use that you can do it with normal drills.

    I'd just chuck the piece and dial it in. Start the hole like usual and open it up to say, .718" then bore is to .75 for as deep as you can with a boring bar. Then start drilling with the longest .75" drill you got. That should get you a fair way in. Then you take a piece of round bar 3/4" say 14" long. It has to be able to slide in the hole you just drilled. You turn one end down to 1/2 or whatever your biggest drill chuck can hold and you drill the other end to take a silver & deming drill. 1 or 2 set screws to hold it in place and you got a long drill. You can go in from both sides of the piece and hope the holes meet or use a longer piece of round bar and drill it all from one end.

    Now is this worth the time? maybe not.
    There may be a size of heavy wall pipe that you could use, perhaps just ream the inside of it to .75".

  6. #6
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    With a .030 wall, a part like that ain't gonna happen at a price anyone would consider reasonable, except the guy who actually does the work. By the time its done, he will figure the price is half what it should be, regardless of how much it may be.

    Attempting to hold any sort of tolerance or finish on a part like this with a cutting tool requires that the tool be piloted near the point of cut. The problem with that approach is chips. They want to go places where you don't want them, particularly between the pilot and the part.

    You might start with a piece of dead soft DOM tubing with a 13/16 OD and 16ga wall, then make and harden a bullet shaped swage tool and PULL it thru the part of the tube that needs to be 3/4 ID. The tube would have to be in tension for this to work, because attempting to push the mandrel thru the tube would likely buckle the tube.

    Another approach would be to make a tool with a bearing on the nose that would ride in the bore of the tube, with a pair of ball bearings set in opposing pockets behind the bearing. This tool could be put in the lathe like a boring bar and fed into the tube. The balls would roll swage the ID to size.

    In either case, you'd still have to turn the OD of the swaged section back to size, but that could be done with a follower rest and a sharp high positive rake turning tool, either HSS or insert type.

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    Well typically such sleeves are glued into place with epoxy, so you will end up with some clearence anyway.

    Bill

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    Use a step drill grind your pilot about 2or 3 thou. overgrove size. Turn the shank to 3/8" use 1/2" rod siver solder to drill . Mount drill on carrage drill out 3 or 4 " clean and move drill out to drill deeper. Dont worry about finish just keep cool the barrel may warp so you will have to strated it

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    step 1, buy a barrel blank in the correct caliber and twist rate, 1" od. rough turned. purchase a chambering reamer. replace the whole friggin barrel , contour it however you like. I don't see what function a 0.030 wall sleeve over the outside of a barrel will give.

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    My first thought was that this must be for something like an old Remington Model 8 or a Mauser 1888 with a long (and thin walled) barrel shroud...

    I would try really really hard to find some source of the correct OD/ID tubing as a stock item, 'cause boring/reaming something like that would be difficult.


    Paul F.

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    Hi Cathead,
    Here's a crazy idea. How's about turning the barrel down to fit what ever size tubing is available. You have lots of choices for tubing material and method of manufacture. Just make the barrel fit the tubing. You'd have much better control of the project.

    Hell, why not buy a 30" 12ga. shotgun barrel off of a single shot (nominal bore is 0.729"). Cut off the chamber, forcing cone, and choke, and you'll still have at least 20 inches. All you need to remove from the rifle barrel is 0.021". Then you can turn the glued on, sweated on, shrunk on, what-ever on, sleeve down to final diameter leaving a 0.040" wall instead of 0.030".

    Good Luck,
    John

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    This could also be for a tension barrel, where a small diameter barrel is run thru a tube and held in tension by threaded nuts. If this is true, tolerances would not be critical. I would ask for more info.

    Rick

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    http://s3.serverdata.com/global-star...drills_ed0.pdf
    We used single and double flute gun drills and reamers for long straight bores.

    Gun Drills

  15. #15
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    Quote Originally Posted by michiganbuck View Post
    http://s3.serverdata.com/global-star...drills_ed0.pdf
    We used single and double flute gun drills and reamers for long straight bores.

    Gun Drills
    Psst...it's a spammer, dredging up a 15 year old thread to spew.

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    Quote Originally Posted by digger doug View Post
    Psst...it's a spammer, dredging up a 15 year old thread to spew.
    So naive....
    Look at his profile page.
    Interests: drilling
    Username: BTA
    And all he does is post links for BTA drills.
    I've seen smarter spammers.................


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