On Friday 05 February 2021 12:03:48 John Dammeyer wrote: > Hi Gene, > But it's also been reported that with LinuxCNC it's possible to stop > the spindle while still in Threading Mode and then turn the spindle by > hand and the carriage will follow. This is of course on a lathe. Not > something you'd do on a mill I think.
I have done in on the mill too, by killinig the spindles psu. it then follows the hand turn in either direction. > The question then becomes what is the minimum number of encoder edges > required to do this without mucking up a thread. A 60 Tooth encoder > gives 240 edges which is still 1.5 degrees. On a 1" shaft being > turned to say 8 TPI with an 8 TPI leadscrew the circumference is 3.14" > or 0.0087222..." per degree or 0.01308333..." per 1.5 degrees. So if > the spindle stops on an edge and then is further rotated by hand > manually for 1.5 degrees the carriage will lag by 0.013" or so before > the system realizes it needs to move. > > My understanding of carbide tooling is that's enough to break the tip. Possibly, probably so, but I have not done the above test while actually cutting. Carbide costs too much. > But if the encoder is 10x that with 2400 lines then at 600 RPM (for > example) we get an encoder edge every 42 uS or so and we've move 0.15 > degrees or and 0.0013083333...". At this point probably not an issue > for carbide and as long as the carriage can track that it's not a > problem. And as long as the system can respond to that encoder change > fast enough. > > See the issue? Another point to consider is, in the g33.1 case, doesn't apply in the G76 case since the tool is backed away before the reversa begings, is the turnarond accompanied by a prior backlash comp move? I don't recall anyone saying in the past. In which case my turnaround programming might cover the backlash move time. As I said before with the new scope I should be able to trace that. In that event motion would need a spindle stopped input so it would have the knowledge to do its own reversal programming. To be really effective, this has to be done in sequence. I cannot just send the reverse on thru from motion without dropping a 20 amp breaker in the service. BTDT, bunches of times. I think I can cobble up a 20 ms time gap to allow the backlash time to get that move completed before unleashing the actual backup value to the pwmgen. But it will have to be sequenced or I'll trip the service breaker. Stay well and safe, John [...] 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
