The SS tube will need substantial wall thickness to not bend inward under the force of the skate bearings. The tubes won't be straight or round, even starting off, less so after clamping and a few jobs. There are many other things about the design that will be biting you in the ass down the line. Try an angle-iron frame rather than wood for the prototype. Also, get a used manual milling machine and lathe; don't try to CNC everything on the prototype, without the kinesthetic learning you'll be handicapped.
The SS tube will need substantial wall thickness to not bend inward under the force of the skate bearings. The tubes won't be straight or round, even starting off, less so after clamping and a few jobs. There are many other things about the design that will be biting you in the ass down the line. Try an angle-iron frame rather than wood for the prototype. Also, get a used manual milling machine and lathe; don't try to CNC everything on the prototype, without the kinesthetic learning you'll be handicapped.