[Zuni]

you might need rubber gasket material on the mating plates!

Yeah. I didn't show it, but I was thinking of a 4"x6" piece of flat inner tube rubber sandwiched between the end plate and the gantry on both ends.

Perhaps I do not understand what you are doing but...

I'm simply pumping coolant down one passage inside the gantry and back up through another passage to cool it:

Spindle cooling I decided also by own way - milling coolant (spec. oil/water emulsion) comes first of to the Spindle, cooling the Spindle and then through spindle to coolant nozzle.

That's quite a good idea, since you already have the coolant in the area of the spindle anyway.

Unfortunately, my machine won't have a cutting lubricant/coolant system, so I was just trying to come up with an extremely simple method to keep the spindle water cool using as few extra components as possible.