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35313Re: [MILL_DRILL] how to drill deep holes

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  • Tom Curlee
    Feb 1, 2014
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      A machinist I used to work with was working on a modification of a motorcycle part that needed a very long, small hole - some kind of oil hole.  I asked how he planned on drilling a long straight hole through a smallish cross section part.  The sequence was:
      - Start the hole with a center drill.
      - Drill the hole with a short shank drill (screw machine bit?).
      - Deepen the hole with a normal length bit.
      - Finish the hole with a long shank or spade bit.

      All the bits should be new or known to be sharp and sharpened correctly.  The key was to start the hole correctly and use the drilled part as a guide for the rest of the hole.  Unfortunately, I never saw the finished product.  I'd be interested in seeing how close exit hole was to the desired position.


      From: Rick Sparber <rgsparber@...>
      To: MILL_DRILL@yahoogroups.com
      Sent: Saturday, February 1, 2014 12:55 PM
      Subject: [MILL_DRILL] how to drill deep holes

      This is a spin off thread from one on reaming deep holes.
      I suppose I could turn the shank down, turn an extension with an OD slightly smaller than the hole, and pin the two together. Never done it.
      I know there are gun drills that can drill very straight holes of any depth but that is way beyond my tool set. It takes a lot more than just a different drill bit:
      In some cases, it would be possible to mill a slot and then close up the top. Then you could get a boring bar in there to round it out.
      What do others do?

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