Specifying Knurls on Prints
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  1. #1
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    Default Specifying Knurls on Prints

    I am specifying a knurl for the first time at work. I've made a few on my own, mostly crappy but sometimes passable.

    I inspected some of the old ones from before I got here. Some are ok, but others downright unacceptable. Double and triple tracked, barely a few thou deep. I could sandblast them for that much grip. I would like to ensure that doesn't happen again.

    These are large (between 1.5" and 3.125") nuts that need a reasonable amount of grip, but won't tear the plastic gloves our workers are always wearing. The material is 316 SS.

    My two questions are:
    1. What would you specify for a nice knurl in regards to finishing with a nice, grippable, but not sharp surface? I was thinking 96 or 128 DP and then finish by cutting the height down some to make some less sharp flats on the tops.
    2. How would you specify this? I was thinking:
      Code:
      DIAMOND KNURL PER ANSI/ASME B94.4-1984, CLASS 1, XX DP
      FINISH TURN TO NOMINAL DIAMETER
      Which would give some "recommended" tolerances for initial sizing? It is surprisingly tight tolerance, I guess it has to be to track well. I'm guessing finish turning to nominal will give me a nice grip without taking too much off?
    3. If I wanted to give machinists choice to cut knurling, how could I specify that as well?


    Unfortunately we will probably go with the same company that goofed on the last ones. Which is why I need to be a bit more anal than the last engineer who only specced: "Diamond Knurl". I'm a bit worried about driving up the price, but if that's what it takes for good parts, so be it.

    GD&T and engineering noob here, so I appreciate any advice.

    TIA,
    COB

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    Turning the top off a diamond knurl in 316..

    That'll be fun to deburr.

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    This might help you a little

    https://www.doriantool.com/wp-conten...inal-Final.pdf

    Hard to spec formed knurls, Cut knurls have specific geometry.

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    Quote Originally Posted by Bobw View Post
    Turning the top off a diamond knurl in 316..

    That'll be fun to deburr.
    Gotcha. Best then to stop it early and not overcut it then?

    Quote Originally Posted by dcsipo View Post
    This might help you a little

    https://www.doriantool.com/wp-conten...inal-Final.pdf

    Hard to spec formed knurls, Cut knurls have specific geometry.
    I see.

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    You're overthinking this.

    If you look into the "math" of knurling, there is supposed to be some magic
    diameter that makes it all work. I've used those #'s, and in my personal
    experience. None of the math matters. Technique is what matters.

    If it was me, I would add a note to the PO, or even the print.

    "No double or triple tracked knurls".. Maybe add a minimum knurl
    depth to the print, and then a note on the PO that knurl depth
    will be checked by feel. The knurl has to work.

    If possible, and it probably is.. Allow for a modified diameter in
    case of double tracking. That way they can just turn off the F'd
    knurl, and re-knurl. That will keep your cost down, and lower the
    pucker factor of your supplier.

    I guess what I'm saying is. Talk to the supplier. I know its nice and handy
    and proper to have it all on the print. But sometimes, you just have to pick
    up the phone to fix the problem.

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    Quote Originally Posted by Bobw View Post
    You're overthinking this.

    If you look into the "math" of knurling, there is supposed to be some magic
    diameter that makes it all work. I've used those #'s, and in my personal
    experience. None of the math matters. Technique is what matters.

    If it was me, I would add a note to the PO, or even the print.

    "No double or triple tracked knurls".. Maybe add a minimum knurl
    depth to the print, and then a note on the PO that knurl depth
    will be checked by feel. The knurl has to work.

    If possible, and it probably is.. Allow for a modified diameter in
    case of double tracking. That way they can just turn off the F'd
    knurl, and re-knurl. That will keep your cost down, and lower the
    pucker factor of your supplier.

    I guess what I'm saying is. Talk to the supplier. I know its nice and handy
    and proper to have it all on the print. But sometimes, you just have to pick
    up the phone to fix the problem.
    Thank you Bob. I've added the note. I will add a tolerance that is +/- the tolerance nominal to within the range for the DP knurl. If they are smart, that will give them 3 chances.

    PS, the magic diameters are for the BS TPI knurls. For DP knurls, the magic diameter is every XX fractional inch.

    I will try to have them quoted by a local supplier who does excellent work. He would never send out double tracked knurls.

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