Prebore and floating reamer holder

Discussion in 'Gun Project Questions & Gunsmithing' started by Shawnba67, Oct 3, 2019.

  1. jrm850

    jrm850

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    This thread kind of ties into the "Lands or grooves" discussion... At least in my little brain. It would be beneficial to pre-bore and use a loose pilot, or no pilot for that matter, for those that dial the grooves in the case of non uniform groove depth. (.0005" difference groove depth in the other thread)
     
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  2. ridgeway

    ridgeway Silver $$ Contributor

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    If it shoots to YOUR standard, then YOUR method is the best....
     
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  3. jkohler

    jkohler

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    I use a gauge pin in both ends to get close then go in with a indicator and dial in off the grooves to get the throat dialed in.
     
    Last edited: Oct 9, 2019
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  4. B Nettesheim

    B Nettesheim Silver $$ Contributor

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    You can get the tailstock back to alignment with the spindle
     
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  5. Clark

    Clark

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    The mathematical relationship between ammo concentricity and accuracy does not exist for chamber concentricity. That is because the ammo is inserted randomly with respect to rotation, but the chamber stays the same.
    Running counter to this is the human instinct to minimize recurrent labor and optimize non recurrent labor.
    So I have dialed in a bore with a 0.0001" intrepid, inserted a custom order 0.0001" increment pin gauge from MSC, got the bore concentric and parallel with the lathe spindle. Then I drilled a 1/2" deep hole in the bore, followed by a clean up with a boring bar for better concentricity, followed by the reamer with a longer than 1/2" pilot. Rinse repeat all the way to headspace in 1/2" deep increments.
    I did this even though I cut the threads off a Rem700 take off barrel with a parting tool on the lathe...and did not debur the chamber hole. When I put in the reamer, it wobbles 0.0070" all the way to headspace. That off center chamber can shoot better than I can.

    Why would I go through an accuracy ritual 70 times more precise than I can shoot? Human nature is to optimize non recurring effort.
     
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  6. Nightraider

    Nightraider

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    It would take welding or shims, which I'm not going to do, especially when the chambers are perfectly to size with no runout, but yes, it can be fixed.
     
  7. Dud

    Dud

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    Shim it and true up everything else. Do cylinder tests, etc.

    It's better than compensating for an out of whack lathe.
     
  8. Nightraider

    Nightraider

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    Not really compensating, I'd perform the same steps if it were 100% true.
     
  9. butchlambert

    butchlambert Site $$ Sponsor

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    If you use a pusher tailstock alignment is superfluous.
     
  10. Dud

    Dud

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    Maybe not the way you chamber, but everything you drill or hold with a live center.

    It's just generally worth doing.
     
  11. butchlambert

    butchlambert Site $$ Sponsor

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    Confused? "but everything you drill or hold with a live center"
    Go back and check my method. I do predrill, but after reaching in and indicating the throat. I taper bore with a small short solid carbide boring bar. I now ream with or without a bushing. I want the reamer to follow the taper bored hole. I do not want a bushing influencing the reamer.
    I hope that clears up the muddy water.
    I'm not taking you to task, just showing why the tailstock is not an issue.
     
  12. Dud

    Dud

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    I'm not the one who is confused.

    I use a lathe for more than chambering jobs.

    It's sloppy to leave a precision tool misaligned if you're going to use it for precision work, even if you can get away with it for one specific job.

    Maybe that's the difference between a gunsmith and a machinist?

    I'm glad I'm a machinist.
     
  13. paperpuncher

    paperpuncher Silver $$ Contributor

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    Another thing to consider is the amount that the tail stock ram is extended can affect alignment as well. This is not always the case but it is something I have encountered. I find that the tail stock is often times a bit higher than the head stock. just my exp YMMV
     
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  14. butchlambert

    butchlambert Site $$ Sponsor

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    Dud, sorry that your panties are in a wad. I may have been doing machine work when you were in diapers. My only comment was if you were chambering the tailstock does not have to be dialed in with a pusher. I don't believe that I posted that you can do all machine work with a tailstock out of TIR. I was not questioning your ability, just clarifying my point.
    Sorry Bud
     
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  15. AckleymanII

    AckleymanII Silver $$ Contributor

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  16. Dud

    Dud

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    No wad here.

    You are reading a lot more in to what I say than my actual words.

    It is a little silly to think that 25 years of experience isn't enough to say align your tailstock.

    I guess you have wisdom on your side or something.

    Without wisdom, I rely on making sure my shit is lined up.
     
  17. butchlambert

    butchlambert Site $$ Sponsor

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    Yep, you were in diapers. Read my post again. I did not question your ability as a chip maker or say that I was smarter. I just said using a pusher does not need an aligned tailstock.
    Have you ever used your cross slide to push your reamer?
    I'm not sure that my "shit" is lined up, but it always hits the bowl.
     
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  18. Lucky Shooter

    Lucky Shooter Gold $$ Contributor

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    Simple rule of thumb-----don't allow what was thought to be nonrecurring turn
    into recurring.

    A. Weldy
     
  19. Dud

    Dud

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    I could do that but I wouldn't feel good about it unless I knew the lathe could pass a cylinder test.

    You know they won't all do that out of the box, right?

    If it could pass a cylinder test and the tailstock was misaligned, the tailstock is still misaligned.

    There is a bit of common courtesy in a machine shop, when you are done with a milling machine and leave a vise attached to the table, you should indicate it square for the next guy.

    The next guy should check it for square too but that bit of courtesy can save their ass if they forget to do that.

    Leaving your tailstock misaligned is similar but if you don't share your shop I guess the only discourtesy is to yourself.
     
  20. Stan Taylor

    Stan Taylor Gold $$ Contributor

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    Butch
    I I'm sorry my friend I didn't realize that I was chambered barrels for my benchrest guns all these years the wrong way I don't prebore I use a reamer for the whole project just think Butch how much wood I would have put on the wall if I would have been doing it the way these guys said to do it.
     

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