Mathematically, you don't need an absolute reference. If you have a perfect mill it would still be a perfect mill if put in on a slanted floor. What matters is the relative angles of the axis.
Yes we can mesure these angles with inexpensive tools assuming you have one "good" larger size square you can trust. Those cheap inductive distance sensors on eBay have sub-micron repeatibilities. They are intended for use as non-contact limit switches and they work well for that. If you put one in a chuck facing down you can detect axis tilt. In fact, you do the same with a dial indictor, Then you scan the sides of your "good" steel square. to detect z-axis tilt. What the system would do is do a scan and see the error. Then it would compute what compensation is required and does the scan again. This way it sees that moving in X or Y no longer effects Z. But there is nothing you can do about tool orientation. Drills and fly cutters can not be fixed but the system could report the angle you would whack it with a mallet then re-test. On Mon, May 11, 2020 at 11:52 AM Gene Heskett <ghesk...@shentel.net> wrote: > > On Monday 11 May 2020 14:22:26 Chris Albertson wrote: > > > So, lets say I have a machine that has non-tricial kinematics (I mill > > with the z-axis tilted 30 degrees) and I write the kinematics routines > > correctly. Then you are saying the machine will not honor accel and > > velocity limits? > > > > But all machines are like this, not 30 degress certainly but some > > number of arcseconds. A nice feature would be to compensate for all > > the errors, not just the bed. > > That then raises the question: What reference point then becomes the one > true reference? Do we have the reasonably priced tools to measure it? > For me that answer is no, but I have observed many times that the hole I > drill by putting the work in the spindle, and a drill straight up from > the bed, are oviously out of alignment by the time that hole is 1" deep, > I am bending the drill. This is likely because it was required I remove > the post while installing the ball screws, and the post is attached to > the base with horizontal bolts into the rear of the base casting, > meaning any slop in those boltholes will allow the post to lean left or > right at least a degree. And it is very noticeable. But, where is the > square that I can use to loosen those 4 bolts that mount the post to the > rear of the base casting, and adjust it for plumb? Such a > _3_ dimensional square isn't for sale that I know of. > > > I would not be surprised if non-trivial kinematics is broken as so few > > people have machines with not-square axis the code would not be well > > tested. That said, te velocity problem is proportional to the cosine > > of the tilt. It is going to be tiny. > > > > On Mon, May 11, 2020 at 11:03 AM andy pugh <bodge...@gmail.com> wrote: > > > On Mon, 11 May 2020 at 18:38, Chris Albertson > <albertson.ch...@gmail.com> wrote: > > > > Perhaps kinematics is the place to do the > > > > bed compensation. > > > > > > We tried that with "probekins" and it turned out not to to work very > > > well. external-offsets seems like a better way as it honours accel > > > and velocity limits. > > > > > > -- > > > atp > > > "A motorcycle is a bicycle with a pandemonium attachment and is > > > designed for the especial use of mechanical geniuses, daredevils and > > > lunatics." > > > — George Fitch, Atlanta Constitution Newspaper, 1912 > > > > > > > > > _______________________________________________ > > > Emc-users mailing list > > > Emc-users@lists.sourceforge.net > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > Cheers, Gene Heskett > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author) > If we desire respect for the law, we must first make the law respectable. > - Louis D. Brandeis > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
