Archie,
 what type of drives have you got? Has this got a toolchanger and a power drawbar of some sort? Just wondering why you are needing ModBUS if it doesnt.
Hood

This Is for this machine   http://jeep534.smugmug.com/gallery/5099973_TQC2C#307649501_owpex
Well here it is. Today's revision of my electronics. all boards from CNC4PC.  I am also planning on re using a transformer I have from another mill to Build a power supply to power the servo's and I am also  going to Build a power supply for the lo voltage stuff and use CNC4PC Regulator Boards where Needed.

Computer Is a 1U rack mount machine.

happy Hunting

No one who has ever known me has ever thought I was shy or Bashful 

Archie,
 what type of drives have you got? Has this got a toolchanger and a power drawbar of some sort? Just wondering why you are needing ModBUS if it doesnt.
Hood

Hood,
Unfortunatly No toolchanger Drawbar Is Air operated, the spindle is NMTB30 and the drives I am planning on using are Larken Viper Drives http://www.larkencnc.com/viper/v200.htm 
the rest is in the above post.

Happy Hunting
archie =) =) =

Looking at the above diag, you could save 3 inputs straight away by connecting all of your home and limit switches in series, there is no real benefit to having them seperate. On my Mill (Beaver NC5) and Lathe I have all of the limits in series but each of my Home switches is seperate, the reason for this however is I have a CNC Building Blocks breakout that can do encoder index pulse homing and it is recommended to have it this way, if you dont use that board then there is no real benefit to having seprate switches. I have seen the arguement that its easier for trouble shooting if a switch goes bad but I cant see how, maybe 2mins saved but 3 or more inputs wasted, but thats just my thinking.
 The only thing I see you need the ModIO for is the  feedrate override (if you are wanting a pot) and possibly the pendant requires it?
All in all it looks good and I think you have most things covered.

Hood