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Scissors type knurling tool question

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  • Scissors type knurling tool question

    Went to the shop for a smoke and before I knew it I was doing something. I got the QCTP mounted and did some turning and threading. Nothing in particular just putting the machine, and myself, through the paces. My post came with a knurler so I figured I'd knurl with it. Cheap, dull chicom wheels which make chinese ratchet knurls... Anyway I figured I'd fool with a scissors type that I got off the bay. Real sturdy cast iron deal with sharp wheels. Couldn't get it to track right. I figure it's gotta be the centering but all I could get was a double track no matter what I tried. Any suggestions?
    I like my lathe...

    Hoffman in Warner Robins Ga

  • #2
    Knurls are like gears. They will cut evenly to a specific diameter. There are some fancy formulas some use to determine the proper diameter for a given pitch, or you can take a light cut and try again until a good profile is obtained. The genterline of the knurls should coincide with the centerline of the work, but eyeballing us usually sufficient.
    Jim H.


    • #3
      Made a lot of knurled parts at the last job. The place had a pretty seat-of-the-pants approach to knurling. If the print called out "medium knurl", we'd dig through the tool drawer and pick one out, hold it up to the light and make like we knew what we were doing, then experiment with the speed and feed until we got a consistently clean knurl.

      The following factors were considered (by trial and error):
      Rate of "plunging" into the material - sometimes creeping in, sometimes getting to full depth within one revolution of the stock.
      Dwell - sometimes pulling out right at one full revolution of the material, sometimes dwelling for a couple seconds before feeding along the material.
      "Depth of Cut" - pushing really hard or just hard enough.
      We rapidly pulled the knurl away when finished if we were thinking straight that day.

      Different guys had their favorite methods ranging from about 100 RPM with no dwell to slamming in at 3000 RPM and pulling away eventually (both extremes are, well, extreme). Basically you might be able to experiment with some of these factors until you get something purdy. Try different pitches of knurls too (we'd even try that if nothing else worked )


      • #4
        I've just knurled a piece of 1.75" OD steel bar.

        I set the scissor knurls approx verticaly centred over the piece and centred horizontally.Put about 1/3 of the wheel width on the end of the bar and tightened the nut until I got a good knurl.Using plenty of cutting oil I then hand traversed at about 90 rpm.

        I don't know if this is the correct way,but it worked.



        • #5
          I've come to the conclusion that knurling might be more art than science. A couple of years ago I made a scissors type knurler per Rudy Kouhoupt's serialized instructions in HSM. I have three pairs of knurling wheels - fine, medium, and course and depending on the diamter of the work piece I'll choose which of the three pair to use. I usually end up doing what JCHannum says - if the first application is goobered up I'll take a fine cut on it and try again with the same wheels, knowing that the wheels will make a nice knurl at some point (without seriously reducing the diameter).


          • #6
            <font face="Verdana, Arial" size="2">Originally posted by hoffman:
            ...I figure it's gotta be the centering but all I could get was a double track no matter what I tried. Any suggestions?

            Centering isn't a big deal. Just eyeball it. Being a little off center won't affect how the knurls track, it will just put a little bit of side pressure on the workpiece, so centering is really important only for slender workpieces.

            Are both knurls double tracking? If so, try starting more agressively (i.e. more pinching force.) You want to start by pressing the knurls deeply on the first turn of the workpiece, so there's a deep pattern for the knurls to drop into on the second turn. Then they will continue to track properly. If only one knurl is double tracking, they might be mismatched by a few thou. Measure them and stone the larger one down to match the smaller. That's what cured my double tracking problem.

            Here's a fairly exhaustive thread which may give you some other useful suggestions:


            • #7
              There was a recent thread on Practical Machinist about knurling (Nov 3rd). There is a relationship between the diameter of the work and the knurl wheels. If the diameter of the work is a multiple (or close) to the diameter of the knurls, knurling will work without overlapping. Otherwise the knurling overlaps and looks bad.


              • #8
                I've been "investigating" the field of knurling
                at school lately. What I did is use the
                coarsest knurls we had ( in a "bump" type ) to
                be able to see the effect of diameter of work
                to knurl. Turns out it's very repeatable and
                perfectly locical. :-) They track right for
                every increase in circumfrence equal to the
                pitch of the knurl. The one I have developed
                the info on is about .070" and the range of
                diameters that will track is about +/- .004"
                When I get all the points I want for this one
                I am going to do it for the sizors type we
                have with a medium knurl. It should make it
                a lot easier for the students to get results
                first time.


                • #9
                  My knurls are 3/4" diameter and have 52 teeth. 52 divided into .750= .014" so the diameter of the stock I am knurling has to
                  a multiple of.014". Of course stock 3/4"
                  which is the same diameter of the knurls
                  comes out perfect.


                  • #10
                    That's close, but we know what you meant. It will actually be more closely tied to circumference. C for 3/4" = 2.356". Divide that by 52 and you find your circumferences need to be a multiple of .0453".

                    Then you have to wonder if it's actually the diameter of the material, or the diameter that your knurl end up while it's into the material, or is it the average of the two or a percent of the "depth of cut", and what does the tracking do as you are feeding in (before you are to full depth), and is it the chord rather than the circumference, ad infinitum. I'm sure there has been a treatise done somewhere about knurling that tries to nail it down to a formula, but how much calculus comes easy for you? Fortunately, knurling is usually pretty forgiving and problems are less common than successes.

                    I think Guero is right - knurling is more an art than a science. Or in my case, more "fiddling around until it works" than art. My evidence is that one day you'll get a CNC lathe working consistently for a whole run, then the next time the job comes up, with a new batch of material and a knurl with the same spec's, the old way fails and you have to fiddle with it again before it works the way you want it to. I think the key is to isolate the factors and adjust one or two while leaving others unchanged. A little harder to do manually, but (at least in my experience) most times it just works OK the first time. Makes me wonder why some jobs cause problems every time while others are cake. :P


                    • #11
                      Seems like I forgot to say .750X Pi=Cir / 52= amount per tooth on knurl.
                      Thank you Vinito


                      • #12
                        Take a look here:


                        A knurl diameter calculator:

                        Location: North Central Texas


                        • #13
                          I've heard the theory on dia. vs tracking.

                          It may or not be true.

                          Frequently in the real (commercial shop) world, the drawing gives start diameters and finish knurl diameters that have to be adheared to.

                          I have knurled tapered belt pulleys on the 2 degree taper with no real problem.

                          I go in hard and fast, on the edge, as mentioned and have had no real problem with tracking.

                          I set the knurl with a little clearance behind the cutting/forming corners. Without this, it is hard to get full depth with the knurl.

                          I have knurled box machine pull rolls that are 5" dia by 100" long.

                          The inspectors for Ward Machine used magnifying glassed to assure the knurls went to a point and were clean.
                          The tolerance end to end was about .005"

                          You need plenty of coolant to flush out, and cool, the knurls for a clean sharp knurl.

                          We used soluable oil with a spout on each knurl. We made a huge scissors knurling tool for those parts. I ran about 120 rpm at .022"/rev feed.

                          Sometimes I leave the stock long so the start area can be turned away to make a nice looking job.

                          Good luck.


                          [This message has been edited by kap pullen (edited 12-09-2004).]


                          • #14
                            &gt;&gt;I've come to the conclusion that knurling might be more art than science.

                            NO, IT'S WITCH CRAFT!!!!!!!!!!!!!!!!


                            • #15
                              I don't think the diameter matters at all. I've knurled a number a shafts and never had to adjust the diameter to make the knurl track. Here is how I do it with my scissors knurler.
                              1. Center the knurls.
                              2. Begin to tighten down while rocking the shaft back and forth (do not turn the shaft all the way around).
                              3. Continue to rock and tighten until the knurl looks deep enough.
                              4. Set the lathe is backgear.
                              5. Set the feed for 0.015".
                              6. Engage the clutch.
                              7. Now start the spindle.
                              10. Oil liberally as the tool moves along.

                              These directions are more less taken directly from the sheet that came with my Eagle Rock knurler. The only thing I added was to use back gear. I found that without coolant I was generating to much heat and ruining the knurlers "axles" if I tried to knurl in direct drive.
                              Also, the feed is key. The first time I accidentally seleceted 0.0015" and it was a disaster.
                              Give it a try. If I can do it, anyone can.