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13082Re: milling a spiral in tube

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  • leasingham_connelly
    Aug 1, 2005
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      --- In mill_drill@yahoogroups.com, "John" <plasmabizkit@y...> wrote:
      > thanks for all your replies i geuss i look intop a sine bar
      > --- In mill_drill@yahoogroups.com, "John" <plasmabizkit@y...> wrote:
      > > i was wanting to mill a spiral in some tube the spiral needs to be
      > > about 3 inches long just wondering to you have to have a cnc
      machine
      > > for that or is there an attatchment you can buy that helps you

      The sine bar will not give an even spiral. As the follower rides up
      the bar the length of its lever will change and the angle of the
      spiral will reduce. Before CNC spiral or helix milling was done with a
      dividing head type of attachment driven by change gears connected to
      the table feed drive.

      Is this a one off?

      How important is the smoothness?

      How important is the angle of the spiral?

      I think it would be possible, though tedius, to do a CNC style of
      table and dividing head dual movement by hand for a one off. You know
      for example that you want 180 degrees of rotation and in 2" of
      movement. This is 90 degrees in 1" or 9 degrees in 100 thou or 1
      degree in 11 thou (roughly). This means for 180 degrees you would make
      180 1 degree turns of a RT or dividing head and 180 11 thou moves of
      the table. Comes in about 20 thou under 2" this way. 2 more degrees
      takes you to 2 thou over 2". Hand finish edges if they are not smooth
      enough for your needs. Make a table in advance of position of RT
      against position of the mill table in case you get confused about
      where you are up to.

      Martin
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