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Re: Touch-Off

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  • mikauvalley
    Hello Guys: [:D] ... repeatability + tool radius inaccuracy ) ... is removed/replaced into the chuck or the chuck is rotated? I d think the chuck slop would
    Message 1 of 10 , Jun 30, 2012
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      Hello Guys::D
      --- In micRo-cnc@yahoogroups.com, Dan Andersson <dan@...> wrote:
      > Chuck slop effect? No, the spindle axis is still stable.
      > The inaccuracy of the repeatability is  +/- ( Spindle runout + micRO repeatability + tool radius inaccuracy )
      > //Dan
      >
      > On Sat, 30 Jun 2012 14:23:15 -0000  micRo-cnc-owner@yahoogroups.com wrote:
      > > What is the repeatability of your X/Y touch offs when the 1/8" rod is removed/replaced into the chuck or the chuck is rotated? I'd think the chuck slop would come into play. Sigh.

      My .0005" touch-off accuracy is based on a 1/8" rod placed in the spindle and not moving.  (With paper jigging, the spindle is running).  So, if I add spindle runout + micRo repeatability + tool radius inaccuracy, I am sure that the accuracy will decrease.  (That is why big and better machines also command a big price).  My main reason for trying to be more accurate in touch-off is because of tool changes with varying z lengths, and registration when flipping to sides or back of stock.   I guess that I should try to figure out how much "slop" the micRo and spindle have.

      > > Also, how do you plan to use this for the Z axis? Each end mill will be of a different length and that length will be inserted into the chuck to a different depth.
      I usually draw geometry as 2d in Cad, and import it into Alibre to convert it to 3d.  I usually center or place one corner of geometry at x=0, y=0, and z=0.  I then add a stock geometry to the 3d drawing that will be the same size as the stock that I will use when milling.  In the Alibre software, I then assign a stock corner as a reference x=0, y=0 and z=0.
      Later, when milling, I do touch-off from that same corner, on the actual stock.  The x and y corners offset will include 1/2 tool radius + touch off plate (if any), which will tell the EMC software where the x,y corner of stock is.  I bring down the end mill tip and touch off at same corner on top of stock (with 0" offset), or touch-off plate (with plate thickness offset), and the EMC software will now know where the top z of the stock is.   (This needs to be done for each varying tool length during tool change).  :( Now the design and the stock are coordinated and milling can proceed.
      When flipping a piece, the registration points must be respectively flipped. 
      > >
      > > My current scheme for the Z axis is that of using a jig. A scrap block of MDF has a hole drilled partially into it so that when a mill is inserted, the remaining part of the mill sticking out is inserted into the spindle collet. Holding the MDF block up against the collet while tightening it insures that the distance from the collet to the mill end is the same for each mill. Better than spending on depth rings which will be out of whack with wear to the mill length.  If you can achieve a constant z lenght, then you will not need to touch-off for different tool lengths. Cool. :)
      > >
      > > After this, I touch off the mill end to my touch off plate on top of the work piece, add the thickness of the plate, and I have my new Z zero. All is automated, one button on my pendant does the touch off, sets the zero point, and backs up/off for clearance.  Cool. :)
      > >
      > > Rick

    • mikauvalley
      Hi Dan: Can you provide pictures of these items? Mikau.
      Message 2 of 10 , Jul 4, 2012
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        Hi Dan:
        Can you provide pictures of these items?
        Mikau.

        --- In micRo-cnc@yahoogroups.com, Dan Andersson <dan@...> wrote:
        > Mikau,
        >
        > I recommend usaing a fixture or jig.
        > I touch off on my fixture. Doing so gives me a 100% repeability.

        > Machine Z touch off?
        > I use a small switch with a rubber covered button. I glued an aluminium cover on the rubber to prevent the tool to sing in the rubber.
      • Dan Andersson
        I ll try Mikau. It s a bit hectic for me as I probably have to sod off to Sweden for a 5 month contract, starting Monday :) The garage is the least visited
        Message 3 of 10 , Jul 4, 2012
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          I'll try Mikau.

          It's a bit hectic for me as I probably have to sod off to Sweden for a 5 month contract, starting Monday :)

          The garage is the least visited place right now...


          Regards

          //Dan

          On Wed, 04 Jul 2012 15:15:02 -0000
          "mikauvalley" <rein.vall@...> wrote:

          > Hi Dan:
          > Can you provide pictures of these items?
          > Mikau.
          >
          > --- In micRo-cnc@yahoogroups.com, Dan Andersson <dan@...> wrote:
          > > Mikau,
          > >
          > > I recommend usaing a fixture or jig.
          > > I touch off on my fixture. Doing so gives me a 100% repeability.
          >
          > > Machine Z touch off?
          > > I use a small switch with a rubber covered button. I glued an aluminium cover on the rubber to prevent the tool to sing in the rubber.
          >
          >
          >
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