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best way to set up barrel bore in lathe?

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  • best way to set up barrel bore in lathe?

    I'm going to try cutting and recrown a rifle barrel in my lathe.

    My headstock is too wide, so I'll have to remove the barrel from the reciever. But I won't be able to use my spider since the barrel will be too short. Thinking about making a plastic 'donut' that is sized to my spindle bore to hold the chamber end of the barrel inside the spindle.

    But for indicating the actual bore of the barrel- what's the best method? I see hardened 'Indicator Rods' from PTG, and I believe they are tapered.

    Or cut a bore diameter brass rod myself? How long should it be?

    How far out of the barrel should you go with the rod for indicators? 6"?

    ...this is new ground for me and looking forward to tinkering.

  • #2
    There a couple of ways.
    1) Use heavy ground wire (I use #6 copper) to protect the threads and clap the 4 jaw over the barrel threads, run the muzzle end in a spider in a steady rest. Indicate directly off the bore or over a gage pin.

    2) chuck the barrel up between centers and align a spider (like shown below), then chuck the spider up in the four jaw and indicate directly off the bore, or off a gage pin.

    This post has the spider covered:
    Go to post number 27
    http://bbs.homeshopmachinist.net/sho...eferrerid=5082
    Last edited by Rusty Marlin; 09-02-2010, 12:38 PM.
    Ignorance is curable through education.

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    • #3
      Barrell set up for crowning

      If all you are going to do is cut it off and recut the crown, then I would use Steve Ackers trick and attach a bushing with body putty near the muzzle. Put a center in the muzzle and true the bushing. Put the steady on the bushing and recrown. The bushing can be removed with a little heat and the finish will not be harmed. The Crown just needs to be perpendicular to the bore at the muzzle.
      Byron Boucher
      Burnet, TX

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      • #4
        Did you make that spider collar? Out of what material?

        I like that idea, if I'm only doing rifle barrels, how long should that collar be? I'd imagine that a longer distance between the spider ends of the collar would give a little better 'resolution' of adjustment.

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        • #5
          Originally posted by Boucher
          If all you are going to do is cut it off and recut the crown, then I would use Steve Ackers trick and attach a bushing with body putty near the muzzle. Put a center in the muzzle and true the bushing. Put the steady on the bushing and recrown. The bushing can be removed with a little heat and the finish will not be harmed. The Crown just needs to be perpendicular to the bore at the muzzle.
          How are you determining that you are perpendicular with the bore with that method?

          Comment


          • #6
            Originally posted by T.Hoffman
            Did you make that spider collar? Out of what material?

            I like that idea, if I'm only doing rifle barrels, how long should that collar be? I'd imagine that a longer distance between the spider ends of the collar would give a little better 'resolution' of adjustment.
            Its made from a peice of 4140 barstock. The set screws are 1/4-20 brass tipped. I made them too.

            I don't remember its dims, but I'll measure it tonight when I get out to the shop. The length was limited by how deep I could get a 1" Silver and Demming drill from one end.

            Longer wouldn't hurt anything, but that one works well for light carbine barrels. Hanging a heavy out the end of it might be a problem, but I don't spin rifle barrels very fast when useing it, 190 RPM tops.
            Ignorance is curable through education.

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            • #7
              This collar mehtod holding the barrel between two centers works fine for threaded barrels, but what about barrels that don't have a 'round' end to the chamber and have a recoil lug on them, like Rem 7400 barrels?

              Here's a pic I found (not mine) of the chamber end:



              Would you make a center that can reach in the chamber for centering?

              I don't think my spindle will fit that recoil lug....

              Comment


              • #8
                Be realistic.

                You have got to pick up somewhere. For a factory 7400 I would either pick up on the OD or throw a brass in the chamber and Pick up on the center of the primer. Yes I know that is picking up some errors. I like to work to close tolerances even when they are not necessary. It hones the skills for when it is necessary. Your going to be working on the muzzle and a little error on the other center 20 inches away is not going to be that significant for cutting the crown.

                Spend $60 and get Grizzley’s DVD on Chambering. Gordy Gritters does an outstandingly good job of explaining the procedure and what you are trying to achieve.

                Go over to PM Gunsmithing forum and search around in the old threads on chambering and crowning. There is a lot of good information there. You just have to find it. I don’t have very good results with the search function. It will be worth your time.
                Byron Boucher
                Burnet, TX

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                • #9
                  Barrel Set up

                  Deprime a piece of brass, put it in the chamber and put a center in the primer pocket.

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                  • #10
                    At first I'll be just tinkering with a normal threaded bolt-action barrel.

                    But when it comes time for working on a 7400-type of barrel, let's say I'd like to cut/crown that barrel. And the recoil lug won't fit in my spindle.

                    What would be the best way to accomplish that? I was thinking about making a bushing or collar that fits on the chamber end with something like 4 brass tipped screws. Then running the barrel between centers (I like that emptied primer brass casing idea!) and indicate the collar to get the collar running true with the bore axis.

                    Then clamping the collar (on the barrel) in the chuck and running the muzzle end out in a steady rest, maybe with another collar out there too since the barrel is tapered....

                    Am I on the right track?

                    I'll do some searching over at PM- thanks!
                    Last edited by T.Hoffman; 09-02-2010, 03:53 PM.

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                    • #11
                      Reread Rusty's first reply. You should put a location in your personal data there is allways a chance that someone is nearby and sometimes it is relevant for other reasons. Anyway it is a good idea to do that.
                      Byron Boucher
                      Burnet, TX

                      Comment


                      • #12
                        Gotcha- thanks! Just trying to soak up as much info as possible from many sources, and sometimes in the blur of information things get passed over.

                        I live in SE Wisconsin btw. I know Obermeyer the barrelmaker is located about 15min from me, fantastic stuff.

                        ....the info that guy has in his head...

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                        • #13
                          You can always extend the chamber to reach your spider. Then you can dial it in anyway you want.
                          Here is an AR15 set up. With a pre-alignment insert for the muzzle, and a aluminum bushing to get real close for the spider end.


                          One for the CZ452

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                          • #14
                            Originally posted by T.Hoffman
                            At first I'll be just tinkering with a normal threaded bolt-action barrel.

                            But when it comes time for working on a 7400-type of barrel, let's say I'd like to cut/crown that barrel. And the recoil lug won't fit in my spindle.

                            What would be the best way to accomplish that?
                            I've never had a 7400 apart. My first two ideas are, 1) its called an independent 4 jaw chuck for a reason, clamp it over that massive recoil lug with the wire protectors and dial in the OD of barrle as close to the chuck as possible with the muzzle end on a center, then I'd dial in my spider and run a steady rest over the spider so the muzzle could be cut.
                            2) pull the barrel extension off and clamp over the threads. ( This may not be possible, But looking at the pic and the schematic I'd bet it comes right off with a set of barrel wrenches.)

                            Here's my copper wire protectors:


                            The spider: 1.5O.D. x 1.0 I.D. x 3.25 long



                            This is the spider for the rear of the head stock. Those are 1/2-20's with brass tips.
                            Last edited by Rusty Marlin; 09-02-2010, 11:55 PM.
                            Ignorance is curable through education.

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                            • #15
                              double tap
                              Last edited by Rusty Marlin; 09-02-2010, 11:56 PM.
                              Ignorance is curable through education.

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