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2716RE: [mill_drill] Tramming Spec?

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  • Duncan McDonald
    Jun 4, 2002
      Message
      Thanks for all the info Stan. I used a lever type DTI that will read down to 0.0005" but not that great an overall distance (0.030"?). Should I use my 1" travel 0.001" reading DI instead?
       
      Duncan
      -----Original Message-----
      From: Stan Stocker [mailto:skstocker@...]
      Sent: Monday, June 03, 2002 10:26 PM
      To: mill_drill@yahoogroups.com
      Subject: Re: [mill_drill] Tramming Spec?

      Hi Duncan;

      A 10 thou out of the crate variation isn't surprising.  You may want to
      clock at several positions around the table, perhaps at 12, 3, 6, and 9
      o'clock.  You'll likely find some front to back as well as side to side
      variation.  Sweep over the table, there is a slight low spot of about 2
      tenths near one of my T slots.  If you end up taking a reading in a
      hollow you'll be chasing weird numbers all night!  I write down the
      numbers, selecting the lowest point, and zeroing the dial of the
      indicator at that point, with about .1 of total indicator motion.  This
      ensures a consistent spring pressure at each reading point.  This is
      assuming you are using a thou reading indicator with 1/2 or more inch of
      travel.  If you are using a tenths reading indicator the available
      travel is much less.  I certainly wouldn't recommend a tenths reading
      indicator until you are down to not more than 1 1/2 thou total variation
      in any case.

      Clean the table with carburetor or brake cleaner before indicating, an
      oil film can vary by over a thou.  Buff the surface with a lint free
      cloth, lint from a paper towel tends to give 2 thou worth of false
      reading.  If you rezero at the same point after each loosen, insert
      shim(s), snug up cycle, you'll be able to tell quickly if you're getting
      things better or not, or if you are making one axis worse before you
      waste too much time. 

      Depending on your patience, you can get to within a thou over 12
      inches.  Getting it down to a few thou total variation is certainly
      worth the time, how far you go past that is just a matter of tweak and
      test.  Figure on a few hours the first time you do this, taking a break
      now and then to avoid a sore back and head :-)  The last thou may well
      take an hour to chase.  Make sure your gibs are adjusted correctly
      before you start or the table may sag slightly.  If you have a large
      domed button tip for your indicator you'll save lots of time lifting the
      tip clear of the T slots.  Vacuum off all of the body filler crumbs
      before cracking the bolts loose, a crumb of bondo under a shim will
      drive you nuts as it powders a bit more with each snugging.  I missed  a
      little bit and wasted around 1/2 an hour before I realized what had
      happened.  Try to snug the bolts evenly and to the same tension each
      time, using a torque wrench wouldn't be unreasonable if you have one
      handy.

      If you need a shim a tad thinner than 1 thou, rolling papers (cigarette
      papers) are one thou thick, and will squeeze down to about 9 tenths.  I
      guess you have to play some old Doobie Brothers if you use papers :-)
      Always fun watching the local quicky store clerks faces when my going
      grey self grabs 2 or 3 packs of Easy Widers!  Rolling papers are handy
      for quick edge finding too, just oil a rolling paper on the side of the
      work and creep the spinning cutter in.  When it justs snicks the paper,
      you're 1 thou from the edge.

      Cheers,
      Stan

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