On Wed, Feb 7, 2018, at 2:35 PM, Chris Albertson wrote: > The G33 says to do a synchronized move. This is physically impossible. > The Z axis has some limit on it's ability to go from zero speed to the > commanded speed. So the controller is reducing the spindle speed so as to > match the ability of the z-axis motor.
Minor (or maybe not) nit to pick here. G33 is NOT like other multi-axis moves. LinuxCNC will NOT reduce the spindle speed based on the limits of your Z axis. You need to choose a spindle speed and thread pitch that are within the capability of your Z axis. You also need to start far enough away from the part that Z will be able to accelerate to match its target speed before it starts cutting. A concrete example: you want to cut a 1/4"-20tpi thread (0.050" lead) at 1000 rpm. Your Z axis needs to be able to move at least 0.050 x 1000 = 50 ipm. If it can't, you will get a bad thread and maybe a following error depending on how your limits are set. In practice, you really need some margin on Z speed, at least 10-20%. > ALL multi-axis moves are this way. You see it best on a milling machine > where perhaps the z-axis is also the slowest. Say you are milling a 45 > degree ramp that climbs upward to the left. The X motor would have to slow > to match the max speed of the z motor. > > When a lathe cuts threads it is in real-life cutting a ramp. The spinach is > turning in x-direction the carnage in z. You can only cut as fast as the > slowest motor can move. And nether of the motors has infinite acceleration. > > On Tue, Jan 30, 2018 at 2:42 PM, <tom-...@bgp.nu> wrote: > > > We have CSS on and are threading with a G33 on our Emco lathe and we are > > seeing the spindle decelerating during the cut. Seems like the spindle > > speed should be fairly steady at a given X location during a G33 and what > > it seems like is that the spindle is still decelerating to speed while it’s > > in the cut rather than before the cut. > > > > We are rapid-ing (G0 in Z) out of the part at the center of the part (X=0) > > and so CSS spins the spindle up to full speed as I’d expect (*) but it > > appears that our spindle is still decelerating to speed as the next > > threading pass is happening. We read that G33 will wait for > > spindle-at-speed before looking for the index pulse. But our > > spindle-at-speed signal seems to be high during the full cycle once the > > spindle speeds up the first time. It seems like spindle-at-speed should go > > low after rapiding out of the part as it moves to it’s next X location and > > decelerates to it’s next speed at the cutting diameter. Or are we > > misunderstanding spindle-at-speed when CSS is in effect? > > > > > > (*) Is it normal that a G0 move also triggers CSS to spin up (or down)? > > Seems like the trajectory planner would know where the next cutting move is > > and not adjust the spindle speed until it needs to. In our case we are > > rapiding out of the part at X=0 and the spindle speeds up when it doesn’t > > really need to. > > > > -Tom > > > > > > ------------------------------------------------------------ > > ------------------ > > 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 > > > > > > -- > > Chris Albertson > Redondo Beach, California > ------------------------------------------------------------------------------ > 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 -- John Kasunich jmkasun...@fastmail.fm ------------------------------------------------------------------------------ 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
