> On Feb 6, 2018, at 11:03 AM, John Kasunich <jmkasun...@fastmail.fm> wrote: > > 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?
Yes, exactly. We calculated what F,K and S values would give us 800 rpm and 80 ipm feed. > 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. I believe we were running the G1 in normal mode, I will try it with feed-per-rev mode as well and see how it compares. > 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? I think I can round up a tach and check it manually. The spindle is controlled by a VFD and we have an encoder on the spindle, but I am wondering if I have it wired (in hal) correctly at this point. I just posted my spindle and encoder config in the thread subject "CSS and spindle-at-speed during a G33” as I was discussing my hal config. > >> 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. I have a readout of the spindle speed showing in Glade that (I think) is coming from the encoder and that number varies about 1-2 RPM at higher speeds (above 1000 rpm or so) and 2-4 rpm at lower speeds. > >> 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. I will take a look at that. Thanks John, -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
