G540 spindle control.

Hi.

I'll try and post here, since it's the only place I can figure out (if there's a better forum for this question, please point it out so I'll post there instead).

I'm planning an X3 mill build (Grizzly GO463 to be precise). I'd like to get full spindle control (speed and direction, but I'm not talking about spindle angular position... yet ;-) )

Someone told me that it's a bad idea to replace the direction switch on an X3 with a relay (the switch's a DPDT switch for spindle current + a SPDT switch for "spindle enable" signal to the spindle control board).

Is it so much a bad idea to use a relay in this manner? I'd take the VFD output from the G540 to the X3's spindle control board (which I read about on CNCZone), one of the G540's output switch for the spindle ON/OFF switch (through a relay), and the other G540's output switch for the direction relay. I could also use a third relay for the spindle enable switch for more safety, but that'd be redundant with the spindle on/off switch AFAIK. (see the wiring diagram below)

What do you think? Do I risk frying the G540 (doubtful) or the spindle control board?

Thanks.

https://lh6.googleusercontent.com/_I...circuitry3.PNG