On Sunday, 6 March 2022 19:57:46 EST andy pugh wrote: > On Sun, 6 Mar 2022 at 22:31, Ralph Stirling > > <ralph.stirl...@wallawalla.edu> wrote: > > plain parallel port stepper control. I'm setting up the > > spindle as step/dir, since he doesn't have analog output. > > He especially wants to be able to do rigid tapping. > > > > I believe I can use the stepgen counts or position-fb > > in place of a spindle encoder > > You sort-of can and sort-of can't. > > It really ought to work, but threading relies in position zeroing at > the index. Encoders just do this, but stepgens don't AFAIK. > > Basically the lack of index-enable in stepgen causes a problem with > this configuration. > > I think that this has been solved on the forum, and I can think of > ways to do it in HAL, but it rather feels like something that should > be built in to stepgen. > > If there is an actual one pulse-per-rev signal provided by the machine > then it's not so hard. Otherwise it is easier with 1:1 gearing and a > bit of a puzzle with not-1:1 > > This is all as I remember it, there might be things that I am unaware > of that are relevant. > For spindles, its best to glue an iron screw to the side of the spindle, and set an ATS-667 hal effect sensor to see it going by, feeding its output back into the encoder as the index pulse. This however, presents a polarity related problem that I haven't entirely solved in my own wet ram. The ATS-667 switches at the center of the screw going by when the spindle is turning one direction but that is kept until the next time the screw approaches, a round-about way of saying that this "index" pulse occurs as the screw is crossing it going one direction, but as the screw is approaching in the other direction, and with a small diameter of spindle where the screw is glued on, can be several degrees which causes the tap to cut a wider thread by cutting on the back side as it backs out. At least thats my thoughts on why mine cuts a sloppy thread. One could use the direction signal to invert the signal but I have not figured out how to blank that switch from being taken as a legit index. What is needed is a way to switch only at the crossing point, regardless of the polarity of the edge from the ATS-667. But which edge is the legit one? > -- > 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, 1940) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
