I'm trying to write a brain to run my rotary tool turret on my lathe.  A little background on the tool change operation first:

When a tool change is called:
1) turret raise solenoid fires to raise the turret off its stop dogs
2) proximity switch sees turret has been raised and allows mach to rotate turret
3) stepper motor rotates turret proper number of degrees
4) stop solenoid fires a stop pawl to give positive stop to turret rotation
5) turret raise solenoid shuts off to drop turret back on stop dogs
6) proximity switch sees turret has dropped and allows mach to continue program

My immediate question is: how do I terminate a lobe to command rotation of a stepper motor a certain number of steps while running g-code which has called for the new tool (i.e. not move via jog)?

Thanks,
-Ryan

I'm guessing since no response that this isn't possible and I need to do the ATC with a macro?

...
how do I... ...command rotation of a stepper motor a certain number of steps while running g-code which has called for the new tool

I think I understand what you are asking. Let me paraphrase to be sure.

You want a single command 'pulse' to provide multiple pulses to your stepper motor driver.

I think you will need some external electronics to do this.

Have a look at: DivisionMaster at http://medw.co.uk/wiki/?page=DivisionMaster (Manual at http://medw.co.uk/liberty/download_file.php?attachment_id=342).  This will do what you want from the box, but it is overkill (function and price) for your application.

A very much simplified version of the same idea is at http://www.diycnc.co.uk/html/onestep.html. This won't work out of the box. You need to interface an electronic monkey to it such that when you kick its arse (the command pulse) it pushes the step button an appropriate number of times.

I am on very dodgy ground here as I know nothing of electronics, but from what I've read at http://www.play-hookey.com/digital/timer_555.html and http://www.eleinmec.com/article.asp?1  I think you could use your command pulse as input to a monostable 555 circuit, whose output acts as input to an astable 555 circuit. The output of the astable circuit is the pulse stream you need for the stepper motor.