> From: Jon Elson [mailto:el...@pico-systems.com] > On 02/05/2021 03:15 AM, Gene Heskett wrote: > > On Friday 05 February 2021 02:57:38 John Dammeyer wrote: > > > >> Granted this subject is a bit old I've now had some time to dive back > >> into the TI F2837xD which has dual processors and other features that > >> will make it a good test bed for trying out stuff. > >> > >> It has a hardware Quadrature Encoder Interface (QEI) so theoretically > >> I should be able to grab encoder counts in any resolution and > >> calculate spindle position relative to Z axis position and create > >> moves to track. > >> > >> I'll report back when I have some more information. > >> John > >> > > As has been told to me, its the time delay between starting the z on the > > passing index, until z has reached the synchronous speed and is then > > locked at whatever phase exists when sync speed has been achieved > No, I'm pretty sure this is not correct. The Z is locked to > the spindle position when the index pulse was detected. > This requires the Z to accelerate PAST the required speed to > follow the thread for a moment, and that's why you want to > cut air for a bit before the tap enters the workpiece. It > is also why you need to leave substantial headroom on the Z > speed to match the tapping velocity. > > Jon
Just accelerating up to speed does work. One doesn't have to go past the speed to catch up to a position. As Andy stated to cut multi-start threads you then just move the BEGIN position further away by the pitch/starts. So a two start thread on a 0.1" pitch is moved 0.05" and then the threading cycle is restarted. Since acceleration up to the spindle speed is constant as long as the spindle speed is the same the tool enters the new thread 180 degrees from the first. However, if the goal of LinuxCNC is to track spindle position from the index pulse then indeed it will have to accelerate past the threading speed to catch up to the threading position. This too will also work with multi-start threading. The difference is the second thread can now be cut at a different RPM because the task of the Trajectory planner is to have the tool enter the work at the same position relative to the index pulse regardless of the spindle speed. That approach is especially handy if for some reason the work was taken out of a chuck and then had to be re-inserted to chase a damaged thread. Now one could turn the spindle by hand in threading mode and 'tweak' the start position until the tool bit entered the existing thread without issue. Or feed hold the threading midway with the X axis outside the thread and then move X in while loosening the chuck and aligning the existing thread with the edges of the cutting tool. In either case, the ability to turn the chuck by hand for threading is useful for repair. For normal threading who cares... John Dammeyer _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
