What is the practicality of cutting 1' x 3' x 1/8" aluminum on a gantry CNC Router?

Background to this question:

I desire to (someday) build a robot chassis similar to those found at
http://www.irobot.com/rwi/.

My thinking would be that I would cut out the parts and then have a local
welder heliarc the sides, etc together for a sturdy frame. The rest would
be bolted together.

The base would be 1/4" aluminum while the sides and rest could be made with
1/8" or thinner if using diamond plate.

Assuming that I following my thinking, the next step is to cut these parts
out. Since I have the parts to make a CNC Gantry router of size: 36" x 36"
I thought that I might use this to do the job. When I purchased my Sherline
Lathe and Mill with the CNC Retrofit, I had the Bill Griffin make me a
complete cable and 4 stepper set so that I could easily connect it to some
future CNC device which I would build.

So, the question comes: Just how practical is it to machine aluminum on a
small Gantry Router? Most small Gantry routers have no mass and I am
concerned that this would make it difficult to cut these parts.

Bill and I have been having this discussion and he noted that although many
vendors (such as Larkin and others) tout their 24" and 36" gantry routers
as capable of cutting aluminum, he has yet to see them actually demonstrate
anything other than wood or plastic at the shows.

I would like to hear from anyone who is or has machine cut thin aluminum
plate of sizes up to 1' x 1' x 1/8" with an occasional piece up to 1/4"
thick?

Speed is not an issue as this is a hobby. Safety and practicality is. Other
options would be to build a cnc plasma table (but that would be a whole new
venture) or just find someone with a CNC router or plasma cutter and farm
out the cuts.

No rush on this, I'm just thinking aloud and would welcome any discussion
on this.

- Eric