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Barrel Crowning On The Lathe

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

  1. 1260engineer

    1260engineer Busy Member

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    Seeings people are talking barrels alot ... i did this while in za cooler . i did it without suds . makes it easier to see
    so it you got some lockdown time
     
  2. fishy-steve

    fishy-steve Engaging Member

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    Why not use a barrel bore pin and clock in with a 4 jaw?
     
  3. Spray1Mark

    Spray1Mark Major Poster

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    Interesting, or as above clock up on a mandrel. My gunsmith when doing any crown be it 11 degree or whatever will always finish by hand with a piloted crowning tool made by PT&G.

    BucketBoy had an interesting technique on here a little while back, HQ grinding the surface or the likes, at the end of the day as long as the interface is smooth and perfectly perpendicular to the bore then that's really all that matters.
     
    Blackmax likes this.
  4. 1260engineer

    1260engineer Busy Member

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    i do sometimes . but as a rule to seft i dont like putting anything in the business end of a barrel . its the last thing the pellet before it goes on its way . and it gets people a bit more skill doing this way . teaches them to look at stuff in more detail. sorry im old school . its worked for me over 40 odd years .
     
    Septic, HW100Tuning, ped and 4 others like this.
  5. Jimmypie

    Jimmypie AGF Leshiy rehoming service

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    Interesting video , obvious burrs or defects and such aside at what point /distance would the regular shooter or even a pro notice an irregular crown affecting accuracy , and by how much “out” should that crown need to be , compared to say the minute differences in a tin of pellets .

    I hope the above makes sense , it does in my head :facepalm::p
     
    Blackmax likes this.
  6. 1260engineer

    1260engineer Busy Member

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    Sorry my engineer geek bit here a proper bit of over the top . i measure the height and depth of lands and fields in my barrels . i make my own head spin sometimes :facepalm:
    its a sad state i know
    if one has toys
    20200509_130302_copy_1209x1612.jpg
     
    ped, fishy-steve and Blackmax like this.
  7. 1260engineer

    1260engineer Busy Member

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    say you had a bure on the left of the crown at close range you would never know . but as the range moves out so does that shot . it will also kick the spin of the pellet as it leves the barrel and as with the rugby ball the spin makes it fly stright . some ask why i dident us a bore pin . the bore pin sits on the rifleing not in it . ive measured rifleing . and you would be surprised some of the things ive found thats why i use poly barrels now .
     
    Blackmax and Jimmypie like this.
  8. Nickg

    Nickg Busy Member

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    Must have missed it, how did you measure how much to shim the jaws?
     
    Blackmax likes this.
  9. hmangphilly

    hmangphilly Posting Addict

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    The pellet sit's on the rifling too .
    Tue Jul 17 22-00-58.jpg
     
  10. hmangphilly

    hmangphilly Posting Addict

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    Lots of ways to skin a cat mate .
    He's using Mk1 eyeball, and finishing the crown with scotchbrite . He says it works for him on 'polyagonal' barrels so fair enough .

    It would knock all the leading corners off normal rifling and create real woolly edges .

    Interesting video Mr engineer , but lots in there not for me .
     
    1260engineer likes this.
  11. 1260engineer

    1260engineer Busy Member

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    the very small chanfer is just on the depth of the rifling . you can see how much you need to move the barrel . some people do packing some people rotate the barrel in the chuck . some people use a bore dowel and work off the offset from a clock . is good question tho . like i said 40 odd years in engineering and you just do stuff without thinking . sometimes it s hard to explain . the main thing is you get the bore in the middle of the chuck :up:
     
  12. hmangphilly

    hmangphilly Posting Addict

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    How are you supporting the other end of the barrel ?
    Plenty of pcp barrels are 500 or so long . That's a lot to be flapping about when you wick up to 1000 rpm .
     
  13. 1260engineer

    1260engineer Busy Member

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    in the back of the lathe is a tapered plug . abit like a collet . that supports the other end of the barrel . i make um out of wood . say my barrel 16.2mm
    i spin a cone up with a long taper . drill a hole through the middle . cut it off then cut it in to 3 and the rest is simple .
     
  14. Nickg

    Nickg Busy Member

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    Your doing it by eye then as I suspected, that wouldn't be close enough for me I am afraid, you need to come off the bore , and as Phil hints at , a spider on the rear of the spindle to get it all running true, very easy to ruin a barrel.
     
    fishy-steve likes this.
  15. 1260engineer

    1260engineer Busy Member

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    I worked for 9 years maching turbine blades working plus or minus half a thou for 10 hour shifts with half hour over lap either end . and was always told by my instructor if you carnt see 5 thou get out of engineering. the old days when man operated the machine .
     
  16. Nickg

    Nickg Busy Member

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    Me too , toolroom surface grinding gap gauges to plus .00015" minus 0 amongst other things , you have to measure it or its scrap.
    Scraped machine beds & slides by hand , setting alignments, have to measure that as well. But hey ho each to there own
     
    fishy-steve and 1260engineer like this.
  17. bucketboy

    bucketboy Very Active

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    I also have an easy foolproof method

    i use a small drill grinder in the tool post set just above centre height.

    The lathes slowly rotates while the grinder does its thing. Because it’s is always removing material perpendicular away from the bore, it leaves a sharp burr free finish 7136C564-7602-4BCA-8BDB-3C423C07F733.jpeg 787392B1-CF8F-43A0-A9E4-2DBF440C2A6F.jpeg D87F6A5B-EEA9-447F-AFE1-3445B3CB941D.jpeg 6D2BA657-08C1-4DE8-952C-8755AD61FBC9.jpeg
     
  18. 1260engineer

    1260engineer Busy Member

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    this is fun :thumb: do gasing and clever stuff and shoot 30 yards 3 shots same hole im happy
    just now :thumb:
    Screenshot_20200513-171737_Gallery_copy_576x1184.jpg Screenshot_20200513-171625_Gallery_copy_576x1184.jpg
     
    Dr. Strangelove and foxtrott like this.
  19. hmangphilly

    hmangphilly Posting Addict

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  20. 1260engineer

    1260engineer Busy Member

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    here you go proper OTT diamond cutter .22
    20200513_174311_copy_1612x1209.jpg
     
    Reefmonkey and Bash like this.

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