In Need of Knurling Help
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  1. #1
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    Default In Need of Knurling Help

    I have very little background in knurling and am struggling to get a good looking knurl on a job I am currently setting up. I am working on a Euro Tech Trofeo 481, Using a 16TPI male diamond single wheel bump knurling tool. Before knurling, I am Turning my blank diameter (material is 303 stainless) to .437 with the hope of achieving a diameter which will allow for an even number of teeth per inch on the part... My goal end diameters .450 +/-.01. To knurl, I am feeding straight onto the part at F:.007 to a depth of .4088 ( 45% of the TPI pitch of my knurl past the turned pre knurl diameter) and allowing the tool to dwell for 1 second at max depth before rapiding directly off the part. Despite following every suggestion I can find online, I am still unable to get a consistent knurl. I have tried adjusting feed in speeds and depths however no matter what I do I cant seem to avoid bad double tracking marks on the part. Any type of suggestions or methods which have proven successful would be greatly appreciated. Thanks.

  2. #2
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    Quote Originally Posted by lhefner View Post
    I have very little background in knurling and am struggling to get a good looking knurl on a job I am currently setting up.
    Not knowing what your budget is or how many you're making, I'd still suggest an Eagle Rock Scissor knurl tool. We have two of them in the shop running on CNCs and getting pretty good results. Bump knurls require a lot of in-feed pressure making them a little rough on CNC ball screws. With the scissor knurl setup all of the pressure is contained in the tool and not loaded on the ball screw.

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  4. #3
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    aj is right that a two die holder would be better- both in terms of force exerted on the machine and double-tracking issues. A two die holder with one left and one right hand (diametral pitch if you don't need to have 16TPI) diagonal knurl should track very nicely, but it would give you a male pattern on your part. You're currently getting a female pattern on your part with a male knurl, so it's up to you if the male pattern would be ok.

    For your current situation, it would be good to know your rpm, width of knurled section, width of knurl, and distance of knurl from collet or chuck. I'd suggest sfm of 50, so an rpm of 440. Hopefully, the knurled section is narrow compared to the knurl width, and hopefully, you're working very close to the collet so it's well supported. Then I'd just play with the blank diameter until the tracking lined up. It might also be worth it to see if you can get good results with the same tool and material in an engine lathe. Sometimes having that feel of knurling helps me figure out a particularly tricky knurl. Another trick is to decrease the rpms as your engaging the knurls then picking the speed up to finish the form.

    It's nothing to do with your double-tracking issue, but I would decrease your dwell at the bottom. Stainless can work-harden when knurled and destroy the knurl dies after a while. It's best to plunge in fast and get out asap.

    If you're still stuck, there's a lot of good info on the Accu-Trak website. I do believe they offer free tech support on the phone as well. Also, the Dorian Tool rep was in our shop yesterday, and he was touting an online calculator they have that will give you diameters for proper knurl alignment. It might be worth connecting with them. Good luck.

  5. #4
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    I've never used a diamond single wheel, always doubles, but I have used single
    straight knurls. Just regular knurling tools, none of that fancy cutting stuff.

    Here is my method. Just a few simple rules.

    I always feed into the part in the X, I never come in in the Z.

    1) Slow to get started.. Pretty much as slow as you can go rev wise.
    2) Get to depth in one single revolution. You usually have to go deeper than the math says.
    Essentially, SLAM it in, .060" a rev or something, pussy footin' around just screws everything up.

    That's it. Once you are in the material, you can pick up the revs to whatever you are
    comfy with, and then feed across in the Z at .007 to .025 a rev..

    If I'm feeding off a shoulder, I'll taper out, otherwise the shoulder gets mangled.

    I can probably count on one hand the number of double knurls I've had in the past
    decade using this method.. Prior to that, hundreds and hundreds of parts with
    double knurls.

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  7. #5
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    I have sold my bump tooling in favor of the scissors as well.

    At one point I was attempting to get the diameter just right as you stated, and when talking to one of the voices at Accu-Trax, they told me to forget that BS. (paraphrased - it's been many years now).

    I've not had issues with it (for the most part) since going to the scissors style.

    On a production run - I might get 1 or 2% doubles?


    ----------------

    Think Snow Eh!
    Ox

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  9. #6
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    I agree with the scissors approach and with with the X. Another item to consider is that the knurling tool and the work diameter have to match. The knurl pitch has to be an integral number of the work diameter just like gearing.

    Tom

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  11. #7
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    In using form knurls in the past, I had to do a lot of experimenting with blank size. Once the proper blank diameter it was pretty consistent using that same diameter with later setups. Keep changing the size by .001 up then down till it tracks right and the finished size is in tolerance.
    Lately I have been using cut knurls and they do not seem anywhere as fussy in getting the blanks size just right. My cut knurls do a little forming I guess since the finished OD will be a little larger (about .001") than before knurling.

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    A scissor knurl is ideal. Check out Form-Roll, they do great work with knurling applications. They have a series of wheels that allows you to get a good knurl on certain sizes of stock, so it's easy to find the right pitch etc. and proper diameter.


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