I have an Emcoturn 120 lathe that has been working with Mach3 for about a year now. The threading wasn't brilliant but ok.
The surface finish was fairly rough. I put the poor surface finish down to the fact my feed rate could only keep up for RPM 's less than about 250.
To combat this I purchased an Ethernet smoothstepper.

I have set the ESS as best I can and there has been vast improvement in the in the smoothness and available speed of my steppers.

However there is one area that is not working properly that is using the G76 threading cycle. Now I have an intermittent fault that is either
 a) each thread pass not picking up previous so effectively removing all peaks from threads or
 b) cutting no thread at all ie going from start of thread cut to clearance position
 (see attached photo) note predicted tool path seems to be correct but the actual tool path does not always match it)

I have tried with programs produced from cam package and using the threading wizards with the same results.

The threads I need to cut the most is M4 with 0.7 pitch. Now with the RPM set to about 500 the feedrate of 0.7 seems to be very constant in the DRO.
I have three LED's set up to help with threading 1) index 2) trigger 3) threading
The index LED seems to be the only one working. (however not sure if they worked in pre ESS days as I never really paid too much attention to them)

The fault seems to be intermittent as even powering down and back up again can change from one to the other.
 I have got to the stage where I am trying to work my way round altering every setting to see what effect that will have, but to no avail.

Any ideas would be greatly appreciated


Just for information my current settings are as follows

Mach3 ver R3.043.062      (when previously turning ok threads I was using a later ver of Mach3)
ESS M3-180220-v4f1-l

controller freq 1 KHz (tried modifying up and down)
spindle 32khz

noise filtering
Encoders/mpg 10.0 (tried modifying up and down)
Misc 10.0 (tried modifying up and down)

Spindle step and dir Pulse width (us) 5.0

stepper settings steps vel acc
x 1280 400 80 (started off with smaller micro steps and
z 1280 400 80 and ended up here)
spindle 1000 120 200

Breakout board Optoport V3 and spindle board V4
I also have an ethernet version pokeys fitted for control panel layout