I have tried running the kernel speed above 25000, but I do hear this periodic "chuck" sound from the motor.
It's louder and more frequent at higher speeds.
In fact, judging by what I can hear running at different rates but the same kernel speed, it's like this "chuck" sound happens after a fixed number of pulses. If I run the motor slower it's still there just less frequent. Which would normally point to some sort of mechanical feature on the screw but I've noticed this on all the axes, including the rotary, so it's not a mechanical thing.
What causes this? Isn't it an inconsistency in speed then, which can decrease its resistance to stalls? It's not losing steps when this happens, is it?
I did tinker with the Active High/Low and Sherline 1/2-pulse. No effect. AFAIK it's an inconsistency in the parallel port's pulse spacing but I can't back that up. Could it be a feature of the G540's drive?
I seem to be limited to about 10 rpm with the Sherline table and a 282oz-in stepper. Going faster (14, 18 rot/sec) runs for like 2 or 3 sec and then a stall.