Hi Gary,
What drivers are you using? Cheap ones don't work as well as good ones.
Unless he is using high quality stepper drives with mid range antiresonance or whatever it is called it will be very hard to get his motors to run 1500rpm while moving a machine and all the accel and deccel that entails. My guess and it is only a guess is that the 48 volts is way too low for his motors. The only way to tell would be to know what his inductance is.
Questions that need to be asked are;
1. what version of Mach is he running? 066 is not recommended.
2. what resolution are the drives set to? Anything beyond 10 microsteps is overkill. 200 steps/rev x 10microsteps x 20 tpi = 40k steps/inch. way overkill on a Taig.
3. What is the motor inductance in mh? This way we can determine the proper voltage.
4. What is the acceleration set to. Too much accell is the easy way to loose steps.
5. If there is a setting for BC speed, what is it set to? since the problem is mostly with BC enabled, try cutting it in half of what it is set too.
More to come as I think of it.
Mike