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degree of taper in a choke?

Discussion in 'Uncategorized Threads' started by skeet_man, Oct 24, 2007.

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  1. skeet_man

    skeet_man Well-Known Member

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    Ok, here's the situation. Say I wanted to make a choke on a lathe. The OAL would be 2.125". I'd like to make a teague style choke w/ no parallel section (tapered throughout). If I wanted to have the muzzle end be .005 tighter than the chamber end, what degree would I need to cut this on? Not looking to do anything soon, just trying to wrap my mind around some concepts for future projects.
     
  2. Neil Winston

    Neil Winston Well-Known Member

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    0.0674 degrees.

    Neil
     
  3. skeet_man

    skeet_man Well-Known Member

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    neil- thanks for the info. Can you share what equation you used to come to that incase I need to use it again?
     
  4. timb99

    timb99 Well-Known Member

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    Skeet man,

    Not sure you want to know what angle, as it will be in hundredths of a degree.

    Essentially, what you're talking about is a cone with an included angle at the point of 0.135° (if I calculate correctly.)
     
  5. timb99

    timb99 Well-Known Member

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    Neil's angle is the angle of one side of the tapered choke.

    The formula, if you have a mathematical calculator, is to take half of the overall constriction you want (0.005/2) then divide that number by the length of the choke, then take the invers tangent (a trigonometric function)

    Therefore atan ((0.005/2)/2.125)

    Which gives you 0.0674° as Neil said.

    What this is, though, is you're trying to cut a conical shape out of the middle of a cylinder.

    Like I said, the vertex of the cone would have an included angle at the point of 0.135° (or two times the angle you calculated.)

    Much easier to show on paper, though.

    Hope this is clear.
     
  6. Neil Winston

    Neil Winston Well-Known Member

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    What you have to do is figure out the angles of a triangle, S_M. Trig's the tool to use.

    So draw a triangle a couple of inches long and with just a bit of "rise" at the far - let's settle on right - end.

    The left end is the angle you need. The far side, the short, short one on the right is called the opposite side and the one on the bottom is called the adjacent side. The length of that short side is 0.0025 inches, since the constriction will be on both sides.

    The sine of an angle in a triangle like this is "opposite divided by adjacent"

    That's 0.0025/2.125.

    That's about 0.0012. "Zero point oh oh one two whats?" you ask. Nothing, really, it's just a ratio.

    But then on your calculator you can find "Arc sin" or "Sin-1" or something and what that does is tell you the numerical size of the angle which has that kind of sin attached to it.

    Try it yourself.

    Neil
     
  7. Neil Winston

    Neil Winston Well-Known Member

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    And the next question for the class is:

    Why, when tim used the tangent and I used the sine, did we get the same answer?

    Neil
     
  8. timb99

    timb99 Well-Known Member

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    Neil,

    I'm astonished.

    Sine is opposite over hypotenuse, not opposite over adjacent.

    That's tangent!!!

    But for such small angles as these, its functionally the same, since there is almost no difference between the adjacent length and the hypotenuse.

    Tim
     
  9. skeet_man

    skeet_man Well-Known Member

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    haha,,thanks guys. This info will get filed away for future use. I haven't used trig since high school 4 years ago, and we haven't gone over it in machining math yet (I went back to school this fall).
     
  10. Neil Winston

    Neil Winston Well-Known Member

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    You are right, tim. I just got lucky.

    S_M, use tim's formula. My trig was 50 years ago, so I hope you will cut me some slack.

    Neil
     
  11. TOOLMAKER 251

    TOOLMAKER 251 Active Member

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    Set your compound on 8 minutes and it will give you .00495 included.
     
  12. skeet_man

    skeet_man Well-Known Member

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    Is there any real verifiable data that a tapered teague style choke will throw better patterns that a traditional choke w/ a parallel of the same constriction (assuming everything else is a constant)? Neil?
     
  13. Neil Winston

    Neil Winston Well-Known Member

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    Mike, I think both of us have probably tired this and run into the same problems. In my case, it was started with the flexibility of a boring tool which doesn't work at all - too flimsy. So enter the proper boring bar, which, it turns out, is too big. Since I passed on the Do-All tool post lathe grinder when it was a couple of hundred/three bucks (and now?) I've just bought tubes since then or bored out tubes in straight-line fashion and settled for the rotten finish because it doesn't seem to make any difference.

    Oberfell and Thompson summarized their best results produced by any tube in their experiment (figure 19) pictured on page 133 of the first (1960) edition. It had a half-inch parallel section.

    Neil
     
  14. hmb

    hmb Well-Known Member

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    On of the best barrel tuners in the trap game uses a one inch parallel section in his chokes. His initials are T.W. HMB
     
  15. biff

    biff Active Member

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    Neil, What effect does the Herb Orre flare do at the end of the barrel, what effect does it have on the pattern? His chokes, the ones I have tried to measure seemed to have a long taper with some parallel and then a short amount of flare. Every one I have patterned did a beautiful circle on paper! Biff
     
  16. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    Biff, years ago there was a local at the Fin&Feather club (Palmdale,Ca.)shooting his mod 12 and had a wad stick in the choke and he fired it again. You could see the bulge just behind the choke on the barrel and it looked weird. The guy shot better scores than ever with that thing than he did prior. He "jugged choked" it, similar to what Herb Orre came up with but his was a lot uglier job than Herb Orre's! Hap
     
  17. biff

    biff Active Member

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    Hap, most of the Ljutics have a slight jug choke in them right before the taper of the choke starts.

    How are you liking Arizona? At least you're gonna be close to the Autumn and Spring Grands! Biff
     
  18. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    Biff, my arthritis and I absolutely love AZ! Yes, the Autum Grand is right around the corner and I'll be there with bells on. It's only 31 minutes from my home to the club! You coming out for either/both? Hap
     
  19. biff

    biff Active Member

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    Hap, as you know--it's a long way from here to there. Besides my sis who lives in Tucson, who I stayed with when I attended the Grands. won't be returning there until the first of December. Sure like shooting there and all the good people I met. Breakem all for me, hope to see your name on the leader board! Biff
     
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