Axis not only has a nice previewer, but it also glosses over some problems with the way G92 works. At some time in the distant past, it was decided that the G92 offsets should be cleared at the end of a program. For a while, I was able to get around this by not putting an M02 at the end of the program, but they took away that little trick, too. So, with the current EMC2, if you pick up coordinates of your workpiece and run a program, the alignment will be reset when the program ends! This is insane, but it is how EMC2 now works. Fortunately, Axis glosses over this mess by resetting the alignment with a G92.3 (I think). You can do this manually, but if you forget, it can cause a crash.
Not at all. I have a VFD driving the stock induction motor, and it runs open-loop. (There are people who have set up the HAL components to make spindle speed closed-loop, but I didn't see the point.) I did have to rig a lowpass filter component in the spindle speed command, because the spindle can reverse fast enough the Z axis has trouble following it.
EMC2 measures the spindle speed and synchs the Z axis to it, and then stays in sync as it reverses and backs out of the hole. You do need a spindle encoder, and this is VERY hard to do the way Bridgeport heads are built. I had to build the encoder INTO the head. See here :
Jon