I think I've run across your current machine and it is of that design, a moving table fixed gantry mill.
Space wise you need longer y-rails and ball screws to move the part past your milling head (rail length = 2x table length).
Might be OK for small designs, but the y-dimension of your gantry envelope vs. the y-dimension of the work piece length (or table) make this not economical for longer tables (strength of ballscrew vs diameter, flex, etc.).
Also the y-drive then needs to work for your heaviest work piece, while for the moving gantry design the moving weight is relatively small/constant.
The only pro I can see is that you get a single drive for the y-axis which means your gantry doesn't skew and that you can build the gantry very heavy to counter flex.
Also, per common wisdom (I'm lazy and will just follow the herd here ;-) ):
https://www.reddit.com/r/CNC/comment...outer_vs_mill/
"I believe the most succinct differentiation is that a mill makes cuts using torque, while a router makes cuts using rotational speed.
A mill will have a heavy structure relative to the working area and will use a spindle with finely grained speed control.
A router will be relatively lighter for the same working area and will mount a high speed spindle, trim router, or full-size router or similar tool."
TL;DR: mill/router doesn't differentiate between the positional arrangement of the axis drives, but only concerns with the cutting force/speed/materials involved.
And portal vs. gantry for cranes doesn't exist, it's the same, thus same should be true for mills/routers, with the caveat that there are no overhead mills/routers which would distinguish the moving column from the fixed column versions (both moving gantry). This might be a reason some manufacturers refer to the ones with fixed columns/moving gantry as portal instead of gantry.
wood, plastic, etc - 1200x800x300
aluminium, mild steel, etc - 1000x300x300
I'm still torn between building a single machine or making two - space available vs money vs reality.
I suppose there is no spindle for hobby kind of money that can cover both, otherwise I'd have come across one by now on this forum I guess.
A BT30 milling spindle with motor in the 1.5-2kW size as a single item/unit seems not to exist either.
This is the example I'm mostly hanging onto for the size/power/capabilities of the machine:
http://www.cnczone.com/forums/uncate...aluminium.html