You can make a tapered thread by specifying the taper in the wizard. I would need to  find my notes on doing it. The taper
input is "twice the angle" ,I think .......  just dont remember. The "T*********xx" in G76 defines the taper.  Been a long time since I  did one.

RICH

Then this is possible make threading conical.

Other restlessness when mach3 turn think implement timing pulse, namely several pulses por revolution of spindle?, i see several turn cnc and all use encoder in spindle.
This must be at least a few slots per revolution for more precision long threads. because several factors can alter the velocity of spindle in one revolution and the mach no informed of this.

thanks
Renato

When using the parallel port Mach just uses a single index when threading and it works well. There used to be an option for multiple slot discs but there was no real benefit to using them.
Hood