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Barrel Crowning On The Lathe

Discussion in 'Technical' started by 1260engineer, May 13, 2020.

  1. hmangphilly

    hmangphilly Posting Addict

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    That applies to a degree even if you don't turn the work .
     
  2. 1260engineer

    1260engineer Busy Member

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    i regrind the jaws on my lathes every year . keeps um running true . :up:
     
  3. Nickg

    Nickg Busy Member

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    If you grind your jaws in situ they will only run true in that one position, it all depends how good the scroll in your chuck has been machined .
     
    fishy-steve likes this.
  4. fishy-steve

    fishy-steve Engaging Member

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    As far as I'm concerned a 3 jaw is for rough work. I have a Pratt 3 jaw chuck that has only .001" runout.
    I also have a Chinese chuck with a little more run out. I use both regularly.
    If I need greater precision then I will use a collet chuck.
    On saying that my most used chuck is a 4 jaw independent. With practice and using two chuck keys you should be able to set up very quickly to better than .0005".
    Steve.
     
  5. 1260engineer

    1260engineer Busy Member

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    i dont ring my jaws do do full grinds as some do . i find that a pointless exercise. its just a wash and brush up . i have sets of soft jaws if i want to do set size stuff . i to use four jaw more than anything else i do milling in my big lathe . angle block vertical slide . tilt twist and so on .
     
    HW100Tuning likes this.
  6. Sarge

    Sarge Posting Addict

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    Some barrels are way out of concentricity, as you say, and some of the better manufacturers seem to be the worst.
    But then it doesn't matter to the bullet/pellet as long as the bore is pointing at the target and the crown is good. the bullet doesn't know and doesn't care.
     
  7. HW100Tuning

    HW100Tuning Get your own Manwich

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    Only if you only ever shoot at one single distance. o_O
     
  8. fishy-steve

    fishy-steve Engaging Member

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    No. It really doesn't matter if the bore is not concentric with the barrel OD.
    If the barrel is bent or the bore and OD are not parallel then it would make a difference.
     
  9. HW100Tuning

    HW100Tuning Get your own Manwich

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    The bore can be nonconcentric and not parallel, they generally are to some degree. Thats why for hundreds of years gun makers work from the bore. The only to guarantee both is to cut the muzzle and breech OD to be concentric with the bore.

    For instance with a PCP air rifle with a barrel that has a parallel but not concentric bore. The breech has to be cut concentric or the pellet might clip when it is pushed into it by a probe, but then if the muzzle is not concentric then the bore to the OD becomes nonparallel.

    So whilst I agree with the technicalities of what you are saying, it doesn't neccessarily work when used in real life applications.
     
  10. fishy-steve

    fishy-steve Engaging Member

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    Totally agree. In my thread;
    https://www.airgunforum.co.uk/community/index.php?threads/air-arms-s310-barrel-problems.299464/
    I've turned both the breach diameter and moderator diameter concentric with the bore. The barrel OD is running out by 0.35mm.
    Both these diameters were originally running concentric with the OD???

    The breech diameter was then sleeved and finished back to size. Again concentric to the bore.
    The moderator diameter was left under size and I made a 1/2 UNC adapter to suit my Weirhauch mod.

    The barrel was also bent. No idea how! To straighten it, as best I can, I had to use considerable force. How anybody manages to bend a barrel accidently on a PCP is beyond me!
    I still have 0.05-0.10mm bend in it but that's the best I can get.
    It's grouping better but not good enough.:facepalm:

    Steve.
     
    Figgy and HW100Tuning like this.
  11. shauny

    shauny Top Poster

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    if you made a unc adp for a weihrauch silencer,it will not fit.hw mods are 1/2" unf :thumb:
     
    fishy-steve likes this.
  12. fishy-steve

    fishy-steve Engaging Member

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    Sorry typo. It is 1/2 UNF. :facepalm:
     
    shauny likes this.
  13. fishy-steve

    fishy-steve Engaging Member

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    It definitely fits.;)

    silencer adapter.jpg
     
  14. Reefmonkey

    Reefmonkey Engaging Member

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    I fit them there Turbine blades:thumb:
     
  15. Figgy

    Figgy Keyboard Hero

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    Fishy-steve try some linear heat to straighten the barrel, warm the side you want it to bend to, metal contracts more as it cools. Used this method to straighten some big heavy pipes and steel over the years, diamond pattern heat and linear straight line heat.
     
    Last edited: May 18, 2020
    fishy-steve likes this.
  16. 1260engineer

    1260engineer Busy Member

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    i did rb2 .spay .pegs . and first v2 500s induction and comps . blades made of quab rolls metal . all you could do with it was grind it with a borazon wheel or black diamond and make holes in it with the old tube eroders . XLO grinders
     
  17. Reefmonkey

    Reefmonkey Engaging Member

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    I just to install and remove alstom gas turbine gt 26 and 13 HP and LP blades and vanes, don't have anything to do with making them,fair play to you there bud.
    I've been to Switzerland to see the process.I may sometimes rework them if damaged but lp end are all CBN coated so not much can be done.
     
  18. Reefmonkey

    Reefmonkey Engaging Member

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    Sorry TBC coated not CBN there tips on HP
     
  19. Reefmonkey

    Reefmonkey Engaging Member

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    This was quite interesting.
     
  20. Septic

    Septic Imagineer

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    .005”?? ... You were being generous to him... Even sheet metal workers used to eyeball press-brake tool clearances at .002” :laff:
     

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