trouble with npt
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  1. #1
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    Default trouble with npt

    I am trying to program an 2" 11.5 npt thread and I having a lot of trouble. to start I have an osp300 control
    I am turning the taper using a lap cycle with an "A" command of 178.2101 which is 1.7899- 180



    so when I turn the OD the taper is good I inspected it in an optical comparator and my taper is only off a few minutes which is in my tolerance and is probably related more to the tailstock runout which is not dialed in perfect but the number I use for my finish od in my lap turning cycle lands somewhere in the middle of the thread length. So I just compensated and made changes to the code on the fly to get to where I want to be but does anyone know a better way to do this?



    also when I go to thread this after I turn the od to the correct size the first pass bites about .100 which is no bueno, that is using the same numbers

    here is what it looks like

    MND=[V2+.012]
    TPR=[[V20/2]*V12]

    v20= taper value so .0625
    v12= thread length




    G00 X[V1+.1]
    G95 G71 X[[V2+[V47*2]]-TPR] Z-[V12+V15+[2*V31]] D[V46] U[V47] H[V1-V2] F[V31*V35] I=TPR B[V50*2] Q[V35] M32 M75
    G00 X[V1+1.0]










    basically does anyone know a better simpler way to turn and thread an od npt

  2. #2
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    Why are you using variables? Why not just use the IGF and program it that way?
    Seems like you're creating too mu ch work for yourself when you can have it programmed in about 1 minute with IGF.

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    Like Dew said or even long hand would be waaay easier, I think your working your self too hard and adding too many variables to your problem (no pun intended)

    G71X=major dia. of small end of OD Z-whatever D=actual thread height from crest to root+difference of small end and big end H=depth of cut per pass F=.0869 I=total taper per set Z value divided by 2.

    Robert

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    only reason for all the variable and local variables is actually for ease of use, my shop makes thread measurement gauges and this program is for threading master setting rings to set the gauges. The variable program was used so every thread size doesn't need its own program, you would be surprised how many sizes there actually are. the smartest thing to do would have been to make a variable driven program specifically for npt tapers but my manager said no, but here I hink I might bypass chain of command and just do that



    Quote Originally Posted by litlerob1 View Post
    Like Dew said or even long hand would be waaay easier, I think your working your self too hard and adding too many variables to your problem (no pun intended)

    G71X=major dia. of small end of OD Z-whatever D=actual thread height from crest to root+difference of small end and big end H=depth of cut per pass F=.0869 I=total taper per set Z value divided by 2.

    Robert

    Thanks, The one thing I was unsure about was the X major diameter. I was unsure if it was small end or large end. with the few that I cut it was ending up in the middle of my Z with no offsets and good tool touch offs

  5. #5
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    Quote Originally Posted by raped ape View Post
    Thanks, The one thing I was unsure about was the X major diameter. I was unsure if it was small end or large end. with the few that I cut it was ending up in the middle of my Z with no offsets and good tool touch offs
    In this case, you can just start out big, using the 1.7899 degree taper and go from there until it fits.
    What I like to do for NPT threads is whenever I make one that I haven't done before, I write down the critical dimensions on a piece of paper and keep them in my box for future reference.
    And then when I make that thread again, I forget where I put it and fumble around making the thread again

  6. #6
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    Quote Originally Posted by Mtndew View Post
    In this case, you can just start out big, using the 1.7899 degree taper and go from there until it fits.
    What I like to do for NPT threads is whenever I make one that I haven't done before, I write down the critical dimensions on a piece of paper and keep them in my box for future reference.
    And then when I make that thread again, I forget where I put it and fumble around making the thread again
    I try to do that too, but always just end up offsetting the threading tool .25" on X and move in on the part. I never seem to get it perfect the first time.

    Robert


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