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Thread: TPF to Degrees?

  1. #1
    WarpToken is offline Plastic
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    Hi,

    Sorry if this has been answered here somewhere already.

    Is there a simple formula to convert taper-per-foot to degrees?

    For example, if I wanted to cut a 3" TPF thread, what would I enter for the angle?

    Thanks,

    -Wes

  2. #2
    Heinz R. Putz is offline Hot Rolled
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    To figure out any angle if you have the 2 sides,you need a trig function calculator with the tangent key.
    Then divide 3 by 12 and hit Inverse Tangent. That will be your angle. The answer is 14.036 degrees.
    NPT thread is 3/4" per foot and to use the Fanuc G76 you have to program the amount of taper over the distance travelled and it comes to 1.79 degrees. Dont forget the value you get as the taper is usually given as a diameter, so to figure the actual taper, you have to take half to figure the angle.
    (From "Simplified Math for CNC" on the website.)
    Heinz.
    http://home.columbus.rr.com/hputz

  3. #3
    WarpToken is offline Plastic
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    So is it possible to use those numbers and cross multiply with your other disired tapers?

    Like a 1.5 TPF would equal 7.018?

    -Wes

  4. #4
    Heinz R. Putz is offline Hot Rolled
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    Do the same as before: Take 1.5 divided by 12, which is .125, hit Inverse Tangent and you get 7.125 degrees.
    Where did you come up with 7.018?
    Heinz.

  5. #5
    WarpToken is offline Plastic
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    I just cross multiplied. 1.5(new taper per foot) X 14.036 (angle of the 3" TPF)and then divided that by 3 to get the new angle =7.018

    Actually in this case it's just half of the other angle since the TPF is half too =)

    But you're telling me that won't work? Why not?

    -Wes

  6. #6
    CPT Crunch is offline Cast Iron
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    It won't work because trig functions aren't that simple. If you graph them, they form almost an S shape. For example, the tangent of 20 is .36397, the tangent of 40 is .8391, and the tangent of 80 is 5.67128.

    There's no easy way around learning trig.

  7. #7
    Heinz R. Putz is offline Hot Rolled
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    Get a trig-function calculator, touch 30, then Tangent. Then touch 15, then Tangent. Look and observe, its not half of 30.
    In my "Simplified Math for CNC" DVD, its a lot longer explanation, but basically its very simple.
    Heinz.
    http://home.columbus.rr.com/hputz

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