I wanted to make the mechanism run quietly even as it ran fast.
Tests showed that even at high microstepping ratios, speeds much over 100 mm/sec resulted in objectionable motor noise. Other sources of noise included the belt teeth hitting the smooth pulleys making a zipping sound.
I did a few things- I stepped up the drive speed from the motors using 1:5 pulleys and loop belts. That let the motors turn slowly even as the mechanism moved fast. At 500mm/sec, the motors are only turning at 1.25 revs/sec.
I installed a Duet WiFi controller board that drives the motors at 256:1 ustepping even at >500 mm/sec (thanks to the 1:5 step-up drive). The motors now run quietly. The wifi connection means I can generate patterns using sandify, transfer the gcode files to the table, and start them drawing, all without the computer having a physical connection to the table. The controller can be hidden under the table.
I also redesigned the Y axis pulley blocks with larger belt pass-through holes to allow twisting the belts so the smooth back side of the belt could ride on the smooth pulleys. That eliminated the zipping noise.
Remaining noise is from the UHMW bearings sliding along the X and Y axes (mostly the Y axis) and some clattering from the pulley bearings. With the sand box on top of the table you can actually hear the quiet grinding of the ball pushing through the sand.
New task: redesign for a glass top that someone gave me and reduce friction in the X axis.