PCW wrote: Stall torque (your 28 inch/lb) is a thermal rating for continuous load.
Peak torque (which is what you are measuring) is 3-5 times
this and determined by the motors and drives maximum current rating
If peak torque should be 3-5x the label rated stall torque, then doesn't my numbers I'm seeing at my ballscrew seem low? Checking numbers here
3 * 28 in/lb = 84 in/lb at servo * (26/14) = 156 in/lb at screw
5 * 28 in/lb = 140 in/lb at servo * (26/14) = 260 in/lb at screw
These numbers seem a lot more along the lines of what I want to see for torque numbers at screw.
andypugh wrote:
greenbuggy wrote: Since I'm gearing down with the toothed belts I'm under the impression torque should be (26/14) * 28 in/lb which gets me 52 (rounded) in/lb
If you want faster rapids you could consider altering the belt ratio. You need to be sure that you have enough peak cutting force still, but with a different gear ratio you will be able to reach a higher peak speed, but possibly at a lower accelleration.
Original servo/resolver setup on this mill when it had a Bandit controller did actually have the X-axis directly driven from the servo. Don't know about the Y-axis as it was MIA when I got the mill. Still, if my motors aren't hitting the torque numbers they should be coupling them directly to the ballscrews isn't going to do me any favors.
I did add in some more FF1 and FF2 starting with numbers suggested here:
gnipsel.com/linuxcnc/tuning/servo.html
Now at 500 FF1 2 FF2 on X
My acceleration is definitely better, have not put a torque wrench back on the screw yet to see if my torque numbers changed at all
Point-to-point times for short moves might actually be longer with a higher peak speed and lower acceleration. How far do your axes have to move at the current settings to reach max speed?
s = v^2 / 2a. Use the INI file numbers for the calcs.
Aren't the numbers in my ini file under axes maximum accel? I can specify far higher accel numbers than the machine seems capable of actually hitting, right now its set at 2.5. How would I go about determining actual acceleration numbers?
If you are wasting a lot of time on rapids, you might want to look at optimising the G-code first. For example does your CAM allow you to switch off full-retract? Certainly in Fusion 360 you can opt to leave the tool down at the cutting height when re-positioning, and it is clever enough to move around the remaining material.
What I've been doing has mostly been 2.5D work so haven't been zipping the Z axis around a lot, but hoping that troubleshooting the accel/torque issues on the heavier-to-move axis on this mill will help me to improve Z as well. Dreaming of a mill I can do HSM on...
