Something to consider about this approach is that the Z axis endpoint will have to depend on the cross slide position, since the carriage and cross slide are effectively locked together. Advancing the cross slide will advance the LS a distance based proportionally on tan(29.5) (or whatever one's favorite angle variation is). Each advance of X will advance Z. So, depending on how the threading job was set up, it's possible the cutter could advance too far into the work as the threading job proceeds. Cutting too deep on Z or crashing the cutter into the work (or worse) is something to think about.
It looks to me like some additional input information to the ELS S/W would be needed in order to set up the threading job so it can proceed in a safe and predictable manner. It would be good to include as many options as possible to make that happen.
In this regard the desired "endpoint" might be indicated by an audible or visible signal to the operator to stop the machine, or perhaps a digital signal to shut the lathe off to get ready for another pass. Since the size and configuration of each lathe can vary the actual method could vary in a pretty substantial fashion, so a generic control signal would likely be the best generically useful approach to address this issue.
I'm having fun here, it's interesting to consider all the things that influence an ELS which can be used in this way.
