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3769Knurling Issues

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  • Jim B.
    Nov 19, 2010
      I note that there has not been a post here for over a month.
      So here is what I have been doing for a while.
      In my restoration of the South-Bend drill press, the thumbwheels that set the
      quill stops needed work. There were only two, there should be three. One of the
      remaining ones was well buggered.
      I needed to make some. The thumbwheel is 1-1/4 in OD 1/4" thick at the knurl
      and has a 1/2 NC thread. The OD has a straight knurl and there are 80 groves in
      the OD. This corresponds to a 64 pitch knurl.
      The two knurling tools I have for my QC TP had diamond knurls in them. I started
      looking for a matching knurl and found most to be expensive.
      I wound up getting a pair of 36 tooth 3/4" diameter, knurls from the UK for
      about $10.
      That's equivalent to the 48 pitch knurl, a bit coarse.
      I loaded the knurls into one of the holders and I decided to test thing out.
      I tool a piece of CRS scrap 1/2" and tried it out. Results were crap. I then
      tried a good piece of OD ground 1144 stock. Remember The OD matches the knurl,
      more or less.
      What I got was ill formed knurls that would randomly change from 48 pitch to 96
      pitch without reason. The picture shows one of each. BTW see that little diamond
      knurled thumbwheel? That was made from the original piece of CRS.
      I thought: "Perhaps the two wheels are not synchronizing up". I started
      knurling, with one knurl on center. I even tried a piece of brass.
      Still ugly and double cut.
      Based on somebody's suggestion I spend several hours honing the knurl (it did
      need it).
      I got tired of making 3/4" thumbscrews and tried larger stock suitable for the
      1-1/4" thumbwheels. This was a piece of 1-5/16 stock
      Double cut a gain but better looking.
      Going to Machineries' Handbook and reading the knurling section, they state that
      diameter is important. I carefully turned the OD to 1.25, I had not done that
      the first time.
      I died the face and brought the knurl lightly into contact. I went one turn plus
      just a bit.
      You can see that the knurl is very close to falling on itself. Over the next
      three knurls I refined the OD just a bit. 0.0025 under 1-1/4 is perfect.
      I was now able to get consistent single knurls and finish the job.

      Proving that size does matter.

      Jim B.
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