On Tue, Feb 6, 2018, at 10:37 AM, [email protected] wrote: > In an effort to optimize our lathe for spindle synchronized motion a > question came up. Should a machine sound the same when running a G1 vs > G33 at identical feeds and speeds? > > When we spin the spindle at, say, 800 rpm and command a G1 move in Z at > 80 ipm the machine sounds different from a G33 move at those same > speeds/feeds.
When you say "same feeds and speeds", do you mean you have selected the F and K and S values such that the actual Z axis speed should be the same? The speed of the Z axis on a G1 move is based on the F word (feed rate) in effect at that time. If you are doing "normal" feed, the F word is in inches per minute (or metric equivalent) and does not depend on spindle speed. If you are doing feed-per-rev, it is F inches per rev of the spindle, and does depend on the spindle speed. The speed of the Z axis on a G33 move is based on the K word (thread pitch) in effect at that time, and always depends on the spindle speed. So in general, those moves will not "sound" the same, since they are at different speeds. Some specific examples Normal feed mode: G94 (set normal feed mode) F6 (set feed to 6" per minute) G1 Z2 (Z moves at 6" per minute, regardless of spindle speed) Feed-per-rev mode: M3 S800 (start spindle at 800 RPM) G95 (set feed-per-rev mode) F0.004 (set feed to 0.004" per rev) G1 Z2 (Z moves at 0.004" x 800 = 3.2" per minute) Spindle sync mode: M3 S800 (start spindle at 800 RPM) G33 Z2 K0.020 (Z moves at 0.020" x 800 = 16" per minute) If you've chosen the F, S, and K values so that the Z axis speeds should be the same, then it gets more complicated. How is your spindle speed set? Do you have a closed loop control such as a VFD with encoder feedback? Maybe (especially if you just have a constant speed motor and gears/belts) the spindle isn't really turning at 800 RPM. In that case, G1 with normal feed will ignore the actual spindle speed and run at the programmed F feed rate, while G33 will track the actual spindle speed, even if it isn't 800 RPM. Do you have a convenient way to independently verify the spindle speed? > Perhaps for the motion planner that is two different code paths but > regardless should the two moves sound identical? G33 waits for index > before moves but once moving is there something going on that would > cause it to sound different than a non-synchronized move? Another possibility is the acceleration up to the cutting speed at the start of the sync move. In some cases, you can have overshoot or speed oscillation as the axis matches speed with the spindle, and that could sound strange. > We are wondering if the difference is sound we are hearing is an > indication of a problem in our spindle or in the way we are tracking > spindle speed. The ultimate way to know what is going on is to use HalScope to view the spindle and Z-axis speeds during the entire move. > > -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 > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users -- John Kasunich [email protected] ------------------------------------------------------------------------------ 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
