> Message: 2 > Date: Sun, 21 Sep 2008 15:37:36 -0400 > From: Kenneth Lerman <[EMAIL PROTECTED]> > Subject: Re: [Emc-users] Perpendicularity of a mill's axes > To: "Enhanced Machine Controller \(EMC\)" > <[email protected]> > Message-ID: <[EMAIL PROTECTED]> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > For the XY axis: > > First bore four holes in a rectangle as large as you can make it. You > want the rectangle to be close to a square to get the most accuracy from > this. Insert dowels into the holes. Now measure the lengths of the > diagonals using a caliper if you have one large enough. > > If not, take a stick and bore a hole in one end to fit the dowels. Mount > the dial caliper on the other end. Use that to measure the difference in > length of the diagonals.
you could also drill two holes in square blocks, clamp them to the table, dial them in with the machine to determine what the diagonal s/b, then measure the diagonal with something. Doing this in several places will give you the information you are needing to calculate the geometric error. A bar with artifacts on the end (of known distance) would allow the same thing. Put spherical balls on each end of the bar. Measure the distance between the spheres (accurately). Set them on your machine, dial them in, calculate the diagonal. This can be a 2D or 3D exersize. > > After that, it's all geometry. > > The Z axis is a little more complicated because there are two issues: > > 1 -- Is the spindle perpendicular to the XY plane? > > 2 -- Is the Z axis travel perpendicular to the XY plane? > > For the first, mount the indicator on a long arm attached to the > spindle. Rotate the spindle by hand and see how the indicator varies. the indicator should be bearing against the table top I use a face plate from a lathe to do this. I put the face plate on the table with three adjustable supports under it. I then use G02/G03 to move the indicator around the face plate to dial it in to the 'motion' of the XY plane (the table top may not be flat or parallel to the 'motion' of the XY plane). Then I use the indicator in the spindle and swing it around the top of the plate to see how far off the spindle axis is from the 'motion' of the XY plane. > The amount of variation will tell you how far out of square the spindle > is. If you plan on drilling holes or milling edges of "square" blocks, > it must be accurate. If you are just carving with the end of a ball > mill, it might not matter as much. If you are drilling holes, this error > cannot be corrected in software. > > For the second, mount a large cylinder with ends that are perpendicular > to the axis on the table (a cylindrical square). Put your indicator on > the Z axis and move it up and down, touching the surface of the > cylinder. Do this on the edge aligned with the X axis and on the edge > aligned with the Y axis. this is exactly correct except :) ken 'how do you put the indicator on the edge of a cylinder?' :) > If you don't have such a square, you should be > able to make a reasonable one on a lathe. If you don't have a lathe, use > a plane square. You should be able to make an accurate square on you > router after you correct the XY axis. > > In principle, misalignment of the axis motion can be corrected in software. > > Whew. I hope I got all of the details right. If not, someone please > correct me. > > Ken > > Christopher Purcell wrote: >> I would like to improve my home-made 3D wood carving router. It has >> stepper-driven 1m long THK ball screws (bless you Ebay) which seem to >> be moving exactly as EMC2 commands, now that I have Helical couplers >> fixing the backlash. The next thing I want to check and maybe tweak >> is the perpendicularity of the 3 axes, which I bolted down using only >> a carpenters square and level as guidance. This is in a home wood >> working shop so the only instrumentation available is a dial >> indicator. If I can measure the axes, then corrections can be included >> in EMC, presumably as hinted at in the kinematics chapter of the >> Integrators handbook. >> >> How do you measure the perpendicularity of 3 axes of a mill? >> >> [EMAIL PROTECTED] >> >> ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
