On Saturday 03 June 2017 05:17:43 andy pugh wrote: > On 3 June 2017 at 01:11, <tom-...@bgp.nu> wrote: > > However, what we were seeing (and have seen multiple times now but > > cannot yet re-create at will) is that even though our routine is > > commanding say, a diameter of .324, the DRO in Axis is showing the > > cutter down below that. Meaning there is a disconnect between the > > commanded position and where the machine is really is. > > Are you displaying commanded or actual position? ie, is the axis not > where LinuxCNC commands it to be, or is LinuxCNC not commanding the > numbers from your G76 command? > > The G76 code is here: > https://github.com/LinuxCNC/linuxcnc/blob/9e4641a816ab8fe4f6a09a48fac5 >50cc8aef1dee/src/emc/rs274ngc/interp_convert.cc#L4590 > > That seems quite explicit: > double end_depth = fabs(k_number) + fabs(i_number); > > And the last moves are cut at start_x - end_depth
I've used g76 in odd ways and while the operation was going faster than the screen DRO updates could track, I haven't been able to touch off at a known diameter, and cut thread based on the pure math entered. And sitting here waiting for my coffee to goto work, I am wondering if there is a g7/g8 interaction thats messing with me? So I commonly start big, and for externals touch off by small increments until the fit is usable. That was obviously by small, about 2 thou increments when I was doing the 50 tpi threads in the x drive for the sheldon. 50 tpi because the walls were thin & I didn't want to weaken it by using a coarser, deeper thread. It also allowed bearing zero clearance much easier to adjust. That seems to be holding well as I set it to zero by feel, and the dial says the backlash is a hair over a thou. I can live with that. And it sure as tooting beat the nominally 90 thou I started with. The screw was good, but the nut was a cobbled up mess, had a helicoil insert in it, running on a square thread screw. And the helicoil was less than 5 thou from being worn and stripped again. I am assuming, never having asked John Knox if the nuts were available, that one would have to make his own replacements. Since I had a small ball screw & nut, that was the obvious choice. I found some oversized balls on ebay, and restuffed the nuts for nearly zero lash. What then is the effect of g7/g8 on g76? 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) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
