Hi Richard,

The 4th axis is generally just used as a rotary axis or slave for 2 motors driving one axis and not used to drive the spindle (although there will always be exceptions  )

The Gecko User's manual (http://www.geckodrive.com/geckodrive-step-motor-drives/g540.html ) gives details of connecting a relay which could be used to switch your spindle on/off - pretty much the same system as you are using at present.

Tweakie.

Hello Tweakie. That's all I needed to know. I'm going to buy a G540 today. It has to be an improvement over the cheap drivers I currently have.

Thank you very much for your help.

Richard V