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Re: ot - polishing out toolmarks on inset surfaces

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  • David Clark
    ... I d suggest maybe a variation on engine turning. This is process where an abrasive disk is used in place of an end mill and pressed onto a surface in an
    Message 1 of 5 , Oct 10, 2007
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      --- In SherlineCNC@yahoogroups.com, "jehancocy" <jehancoc@...> wrote:
      >
      > I added a folder called jth polishing to the files section of the
      > group.
      >
      > The box is 2" long, 1.5"wide and 1.1" high. The holes in the box
      > are .5" diameter for scale. Notice in this rendering that the
      > insets are bead blasted rough and the outsets(?) are polished. I
      > want to reverse this but you can see from the file doing it
      > completely with sandpaper without damaging the sharp edges will be
      > tough. the insets are .025 on the back and .02 otherwise. The
      > bottoms of the insets are flat.
      >


      I'd suggest maybe a variation on engine turning. This is process where
      an abrasive disk is used in place of an end mill and pressed onto a
      surface in an overlapping pattern. Sort of like fish scales. If you
      search on "engine turning" you'll find some examples. I'm pretty sure
      some other members have done this.

      What you might try is using a wooden dowel loaded with lapping
      compound in place of the end mill and run the same program that milled
      the pockets with different tool radii and offsets. Maybe even make a
      spring loaded polishing tool of wood or brass. Also, Dremel sells
      polishing tools already impregnated with compound, might be worth a try.

      Another approach, I have a rotary abrasive tumbler. It's an El
      Cheapo, less than $100 at Harbor Freight, but works well since I
      reassembled it with good hardware and plenty of LocTite after it fell
      apart the first time. With ceramic media it takes all the tool marks
      off of brass in about an hour. The resulting matte finish is then
      fairly easy to polish.

      I'll be very interested in how you make out. Don't think this is off
      topic at all.

      DC
    • jehancocy
      Dave, I just spent 1/2 hour with a dremel hard bristle brush and some 600 grit lapping compound. It doesn t look bad but this was only one inset and that
      Message 2 of 5 , Oct 10, 2007
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        Dave, I just spent 1/2 hour with a dremel hard bristle brush and
        some 600 grit lapping compound. It doesn't look bad but this was
        only one inset and that leaves 15 to go.

        On the top and other flat spots, I take it to 2k grit wet sand paper
        and then just use Flitz and it comes up to a mirror shine.

        The tool marks are very slight. I used a 4flt 1/8 cutter running at
        about 4k rpm and 5ipm to cut the insets. I used my larger r45 cnc
        mill which is very solid and rigid.

        I considered engine turning with a 1/8 spring loaded dowel but
        thought the bead blasting would give it more of a cast block look.
        My kids, the recipient of the engines, thought the polished insets
        looked better.

        I am going to look for the impregnated brushes. I know 3m makes
        them - I didn't know dremel also.

        What I need is a 1/8" random orbit sander!
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