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32362Re: [mill_drill] Round Column Mill Laser Head Alignment - Again??

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  • js1160@yahoo.com
    Feb 1, 2013
      I'm not quite sure of your intented use of this alignment process.  Is it the ability to move the head and then bring it back to the exact original position?  Or is it to raise/lower the head in a true vertical?

      Objective one is easily accomplished with test indicators at the mill table.

      Objective two requires that your mill column be parallel to the plumb line that is 15 ft away.  And this doesn't account for the possibility that the column is not trammed to the table.

      If you're getting visible laser dispersions already at 15 ft, you need to get another laser.  Instead of using a screw as the target, use a photoreceptor hooked to a buzzer or light.  This target is much smaller and will eliminate your subjective or parallax errors.




      From: lytle78 <lytle78@...>
      To: mill_drill@yahoogroups.com
      Sent: Thursday, January 31, 2013 11:18 PM
      Subject: [mill_drill] Round Column Mill Laser Head Alignment - Again??

       
      After a long layoff due to winding up my working life and a couple of months of catching up on overdue stuff, I'm back to contemplating the mess left behind when I stopped working in my shop about eight years ago.

      One thing I'm struggling what to do with my Mill drill. It's a Taiwan model - I think it's pretty good quality all things considered but it sure takes up a lot of room.

      The endless puzzle of losing head registration when raising or lowering the head has fascinated me way more than it should have. It's the kind of practical/theoretical problem that I love to puzzle over and somehow never get around to actually Sorting out.

      I posted a while back about using a laser which projects a line- aligning it with a plumbob string on the wall opposite and using that to align the head. The line is only used to Set up the laser line projection in a more or less vertical alignment using a rotating front piece on the laser.

      The actual target is a Phillips screw head which suspends the plumb line. The laser is on the side of the head and points at the wall about 15 ft. away. I have now tested system by setting up a 123 block in the mill vice and butting the side of the spindle against it. I adjust the laser to shine in the screw head and begin testing.

      The laser line is actually just a series of dots butted one up against the other and as you get further away from the source and further from the center of the beam of the laser along the line, the dots kind of spread out. On the screw head I typically see two dots, And although these Laser dots are distributions of kind of swarming little particles of light and therefore not really sharply defined, it's really quite easy to see where on the screw head they fall - the "cross" in the center - on the right or left half - or just touching the edge.

      The first test was to see if I could rotate the head away from the stop it was butted up against and then rotate it back against the stop and have the laser dots fall on the same place on the screw head that they did in the initial set up. They did this quite reliably and I'm satisfied that the repeatability side to side like that is good. It is however not very useful information in itself because the real problem is raising and lowering the head not rotating it from side to side.

      I did however want to measure the sensitivity of the position of the dots on the screw head to angular misalignment of the head and therefore misalignment of the position of the center of the spindle. To do this I put a shim made out of three thicknesses of auminum foil measuring approximately 1 1/2 thousandths of an inch between the stop and the spindle and observed the displacement of the dots on the screw head as a result. The resulting displacement was easy to observe and amounted to perhaps a quarter of the width of the screw head in terms of position the dots.

      I was now satisfied as to the repeatability of the readings and also had tested the sensitivity of angular misalignment that made me confident that I could repeat within about 2 thousanths of an inch by positioning the head so that the dots on the screw head appeared after adjustment in the same position on the screwhead that they had before the adjustment.

      Now it was time to test a realistic case. With the head low on the column I adjusted the spindle against the stop - adjusted the laser on the center of the screw head and then raised the head about 4 inches. I then lowered the spindle the corresponding amount and grounded the spindle against the stop. I then observed the position of the laser dots on the screw head. I was delighted to see that the displacement was minimal - corresponding roughly to the displacement I had observed with the slightly over 1000 th of an inch shim that used in the previous test.

      I'll work on this more over the rest of this week and the weekend and hopefully post pictures in the photo section illustrating the process and maybe make a little YouTube video.

      On the other hand if I've overlooked something and upon further experimentation the whole thing turns to crap I'll let you know by posting here.



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