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In my experience Mach3 coordinates the rotational feedrate to match the linear feedrate in a coordinated move.
The build in question is a Fenby Corliss and the helix is for the goveneror to alter the valve timing ( i think )
How did Anthony do it as I don't think he has CNC?I would think it could be done with small movements of a rotary table and equally small movements of the mill then a lick with a fine needle file.J