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Thread: Online Knurling Calculator

  1. #21
    PJs
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    Quote Originally Posted by rgsparber View Post
    You can find a sample of knurling a taper at http://rick.sparber.org/knu.pdf. Sorry, but diameter is not a critical parameter. Rick
    Thanks for chiming in with your thoughts Rick...although I disagree that diameter doesn't matter, mainly because of things I brought forward in my dissertation. Like Paul, I get clean, sharp, Consistent knurls every time by using the calculator, but each to his own devices. In my research I talked with a lot of people about it, but there were a couple of old timers that said they just "jam it in" till you get a good one. The inconsistencies I got by the "press on" approach, cost me a lot of parts...plus all the other variables make it even more difficult to achieve every time. I like sharp clean knurls mainly because I make a lot of small stuff <2" (max of my scissor) and only have a tiny import lathe that only dreams of being a Hardinge HVL-H or a Clausing.

    Paul, I agree about brass and use it quite of bit for thumbscrews and such. Turning by hand does give the best result I feel, but sometimes do it at lowest speed (~150) for maybe 15 seconds at a time, with pretty darn good results...especially if I'm within a thou or so of diameter. I spritz with WD when under power and seems to help push the flakes away...with safety glasses of course. Interesting Idea about using chalk?? I would think it might cake in the knurl tool and not give sharp peaks under that kind of pressure.

    FYI for everyone: On my little website, Google has finally killed not only my Online Calculator but also my Contact Me form. They appear to have gone to the almighty App approach to these things. Honestly I don't have it in me anymore to fiddle with the Online Calculator version anymore than I have already and don't want to learn Another language or sort through their help/forum stuff at this stage of my life. I did find a back door to the email but its a pain also. If anyone on the forum would like a copy of the Excel spreadsheet, you can PM me here with an email address to send it to and I am happy to share and send it!

    Till Then, May your knurls be Clean, Crisp and Consistent!!
    ~PJ
    ‘‘Always do right. This will gratify some people and astonish the rest.’’
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  3. #22
    mklotz mklotz's Avatar
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    I must agree with everything PJ says. I too have had problems with the "jam it in" approach and regularly calculate the correct diameter for knurling. Since doing this, I've never had a botched knurl. Jamming will often work but calculation always works is my motto.

    I use heavy sulfurated cutting oil liberally applied from a squirt oiler when knurling. It seems to float the chips away fairly well. A flood oiler would be better but too messy for me. For very long knurls I use my drip oiler described here...

    Parting-off oiler

    I always use the slowest backgear speed on the lathe for knurling.

    There's a knurling diameter calculator on my page (see my sig for URL) but, like PJ, it's a victim of the march of time. It's written to run in DOS so you need to install a DOS emulator to run it. The procedure is described on my page.

    Actually, the calculation is quite straightforward and can be done with a calculator. It depends on the fact that the circumference of the workpiece should be an integral multiple of the pitch of the knurl.

    Calculate the circular pitch of the knurl (p) by dividing the knurl circumference (pi * diameter) by the number of teeth on the knurl.

    Divide the circumference of the workpiece (pi * diameter) by p to obtain a number (n). In general n will not be an integer. Truncate n to an integer.

    Calculate the workpiece knurling diameter = n*p/pi
    ---
    Regards, Marv


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  5. #23
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    Marv and PJs,

    Knurling with the "jam it in" approach has never worked well for me. Taking the time to calculate the correct diameter produces perfect knurls for me but I do my knurling early in the order of machining steps, if possible, so if somethings does go wrong, it is not a big loss of machining time.

    By the way as they say "there's an app for that". For the last year, I have been using an Android phone app entitled "Knurling Calculator" with a lot of success. The knurl specs and diameters are in inches but that works for me since all my straight and diamond pattern knurl wheels have Imperial based pitches.

    Paul Jones

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    Like you, I try to plan to do the knurling early in the construction. Whenever possible/convenient, I'll knurl a bit farther than actually required and throw the remnant in the next-time-I-need-to-make-a-knurled-screw-for-something bin. I hate to set up the knurling tool just to make one little screw.

    Actually, I think knurling is somewhat overrated. It's fine for an adjustment screw that's used infrequently, e.g., a micrometer barrel or the lockscrew on a caliper, but, for surfaces that are handled often or must be gripped strongly flutes are far easier on the hands. Better yet in some cases is no roughening at all.

    I have several inherited tap wrenches that had knurled handles. I long ago turned the knurls off or covered them with shrink tubing. I've seen knurled die holders for the lathe and thought "ouch"; what happens when one of those grabs?
    ---
    Regards, Marv


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    On aluminum I do use WD-40, go slow, and just jam it in and hang on. Since it is a scissors arrangement, there is no stress on the spindle.

    I think my tapered and knurled sample demonstrates my claim about diameter. If you are careful selecting the diameter, the knurling can come out right. No argument there.
    Rick

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    I've seen the knurled taper counter-example before; it's a constant riposte to the calculation approach by John Stevenson, who some of you may have encountered in metalworking fora.

    I have my doubts about what it proves. My feeling is that, once the knurling "takes hold" and is producing a consistent knurl, it will track from that knurl as the tool is moved left onto stock of slightly larger diameter. This effect might even overcome a step diameter transition instead of a gentle taper.

    To my mind, the acid test would be to turn a piece to the exactly calculated wrong diameter* and then, using a very fine knurl (so there's little space to squish stock into), show that jamming will produce a correct knurl.

    I'd do the test myself but I'm too lazy and, whatever the result, nobody would be convinced to change the way he works. :-)

    --
    * work diameter = [(n+1/2) * knurl pitch]/pi for n an integer
    ---
    Regards, Marv


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  12. #27
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    Quote Originally Posted by Paul Jones View Post
    Marv and PJs,

    By the way as they say "there's an app for that". For the last year, I have been using an Android phone app entitled "Knurling Calculator" with a lot of success. The knurl specs and diameters are in inches but that works for me since all my straight and diamond pattern knurl wheels have Imperial based pitches.

    Paul Jones
    Thanks Paul for putting that in here. I did try out that app back when you turned me on to it. I did a large sample of comparisons to my spreadsheet and found it within a thou or two of my calculator across the range. I also tried it on a few operations with good results. For most users it will work very well, IMHO. The thing about Apps to me are the Eula's...does anyone read those things but me?

    Marv and Paul,

    Thanks Marv, love the simplicity of how you put the formulas in perspective. The difference in "My Method" is that I actually measured and counted teeth on each of the wheel pitches using two methods to calculate Pot/CP and the PF (CP/Pi) as accurately as I could for My knurls. I found that every knurl wheel diameter that I measured was slightly different, including TIR. I would think that Dorian or other quality wheels would be more consistent but then there is the whole Spec thing and which spec is used on manufacturing CP knurls. Dorian for example uses a percentage of CP as tooth depth and nothing about the Illusive Nominal diameter (Dnt). CP knurls are an illusive bunch but the oldest and most common out there! DP wheels have to meet ANSI spec...but the formulas/algorithms work on both.

    Basically I built the spreadsheet to be able to enter your wheel data (if you take the time to measure and count) to get as close as possible with out knowing the tooth depth. I also included a calculator (cell) for how much you have left to take off so you can just set the dial on the cross slide for your last cut before knurling, which I find handy. I use it on my tablet in the shop and have that App as well.

    Thanks much for chiming in here. ~PJ
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  14. #28
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    Marv,

    I wonder if the "jam it in approach" works because there is a small amount of leeway in the deforming of the metal. Call it the "fudge factor". When the diameter of the stock is large enough, the needed amount of deformation is small enough to be accommodated. Say I have a cylinder of infinite diameter. Then the knurling teeth simply run on the surface never engage with the previous impression. Therefore there cannot be any misaligned reprint. Next, picture a diameter that is very small. The first tooth makes an imprint and the second tooth misaligns with this imprint. There is no way to cleanly knurl this diameter stock. So there are the limits.

    Say the knurl can deform the surface such that the diameter becomes an integer multiple of the pitch. This would give a clean pattern down to some minimum diameter. As the diameter becomes smaller, this fudge factor becomes a larger percentage of the total diameter and I expect that it becomes more difficult to apply enough force to make it work. Clearly, when this fudge factor equals the diameter, it all falls apart.

    Do these ramblings make any sense to you (or others)?

    Rick
    Rick

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  16. #29
    mklotz mklotz's Avatar
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    Rick,

    Yes, I think you are on the money. That's why, in my suggested experiment, I specified a very fine pitch knurl. Such a knurl will have less room between the teeth into which the metal might deform. It will tend to "roll" over the surface leaving a trail rather than pushing the metal aside in order to create the pattern.

    I hadn't given much thought to minimum knurling diameters but, again, I think you've captured what will happen.
    ---
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  18. #30
    PJs
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    Rick & Marv,

    I kind of get this, maybe(¿), but more from an empirical approach than theoretical with fudge factors. I have found generally that even with the formula the smaller diameters with a coarse wheel don't turn out as well (not as crisp or defined). My thoughts on this phenomenon were because of the depth of tooth differential between the Coarse and Fine wheels and the ratios of that to the material diameter¿ I also think there is some "Fudge Factor" due to using CP Wheels which typically don't have a design spec for tooth depth other than maybe a % of the illusive "Circular Pitch" and no known DNT...which is a "Nominal" diameter anyway. Again all the other factors, materials, tool rigidity, alignment, quality of wheels, etc. become much more prominent on smaller material when "Forming".

    I have successfully made decent fine knurls down to slightly less than .188 and course down to ~.25 but anything less and they muddle a bit. I would also suspect there is a muddling of fine knurls on diameters larger than X but have used them up to about 1" successfully...just doesn't feel like it fits the need on larger stock other than maybe some loose press fit with straight knurls.

    In Ricks scenario would this theory work for non standard size material with DP Wheels as well? Additionally the Q factor (empirical correction factor for tracking) supplied by the ANSI standard is quite small and divided by Pi to determine the DOT of the wheel. DOT=Dnt-(Nt*Q/Pi) I personally would like to understand how this Q factor is found and try to understand the geometry/math of it.

    Or is all of this a case for what defines a "Good Knurl?

    ~PJ
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