Hi
I am in the process of buying things to build a gantry router with a cutting area of about 600x900mm with two steppers on the x-axis so I can mill the top of large things if I want to.

I was going to make most of the frame out of Aluminium profile, but I have noticed that there are no surfaces in my house that are flat to within a couple of mm let alone anything like the tolerances I would want in a router, and if I am not careful it is all going to end up on the squiff.

A spirit level seems a bit lacking in accuracy, and that is where my imagination has stopped so far. Are there any neat machinist tricks to get around a lack of planar tables? or am I going to have to see if I can borrow a flat surface somewhere on which to do up all the bolts?
thanks