On Monday 01 January 2018 18:59:08 John Dammeyer wrote: > Most of those VFDs appear to be open loop. > > What's normally done with LinuxCNC for closed loop spindle control? > Say you want to do the equivalent of internal threading on a lathe. > Is a run-out area required or can LinuxCNC control the spindle speed > in sync with the Z axis so either a tap or cutter follows the threads? > > Is an AC Servo (with encoder) even required on a CNC system or just > open loop variable speed control? > > Thanks > John > All thats needed is a reliable way to track the spindle as it turns.
>From that and the 1/tpi or tpmm of the tap, the rest of the required motion to carry the tap into the hole in synch with the taps own threads, and a reversable spindle to back the tap out of the hole, totally in synch with the taps own threads. This is G33.1 at work. Switching from a tap to a single tooth, usually triangular cutter, (using G76) will drive the cutter at the desired number of threads per unit of travel again to cut the thread, retracting the cutter over a programable distance at the end of the thread, or drive the tool into the thread at the beginning of the cut or both. Here the spindle synch is disconnected at the end of the cut, the tool is taken back to a point about 1 turn away from the start of the thread, and synchronized motion is re-established at the next index pulse from the encoder on the spindle. Here also, the tool is driven at 29.5 to 30 degrees as its driven into thread so that the cutting action is only on the leading edge of the tool, much cleaner cut. G76 has the concept of a drive line, which can be adjusted for increased clearance during the tools retrace move, this and the length of the extraction move can be exploited to make tapered threads with very low taper angles. That in turn can make an extremely high pressure compression joint for attaching a extended drive shaft to the end of a ball screw. > Both of those 2 gcodes need carefull study. They can be very powerfull when used correctly. > > > > > > ---------------------------------------------------------------------- >-------- 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 > [email protected] > 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) 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
