Originally Posted by
joeavaerage
Hi,
in order to do threading YOU MUST have an index signal, it doesn't matter particularly form where it comes so long as it fires once and once only per rev.
Traditionally the ESS, and many other controllers, used the index signal not only to synchronize the start of the thread but as a signal by which to calculate
the spindle rpm. In more recent times the ESS can accept multiple pulses per rev and use that to calculate the spindle rpm. The advantage being that the calculation
happens many times per rev and therefore Mach is updated as to the actual rpm that much sooner.
The source of the multi pulse per rev signal is not important. Thus I believe you could use one channel of your spindle mounted encoder and a hall sensor,
if it has one, as an index signal. Alternately you could mount a separate hall sensor for an index signal.
Having a timely and accurate spindle speed allows Mach to fine tune the Z axis advance per rev, or the pitch. Having said that Mach calculates the Z axis advance only
once per rev so any increase in the accuracy of the spindle speed offers only a marginal increase in thread accuracy.
Mach has traditionally relied on the spindle speed being constant, or very nearly so. That requires a spindle with large angular inertia and/or a high torque drive
such that the cutting forces do not adversely affect the spindle speed.
The ESS in the Mach4 plugin (note this is NOT implemented in the Mach3 plugin) allows for spindle PID. Thus if your spindle is speed controlled by
a PWM signal, the multi pulse per rev (encoder) signal can adjust the PWM duty cycle to maintain programmed speed. This means a spindle
of low or marginal rotational inertia or spindle power can maintain a constant spindle speed irrespective of cutting load. Thus there is a distinct
advantage to using Mach4 and the ESS.
Craig