Homebrew PCBs

today i saw some square steel material, about 1" in dimension (yeah i just 
used your fu***** non metric system ;-) )

it seems to be accurate, but one side is welded in the middle.

i see two options: using 4 ball bearings and 2 spring loaded.
sand down the welding residue (not too much on the outside) and use a 
spring loaded bearing this side (needs not to be accurate then)
advantage: symmetrical load
disadvantage: you have to use the sanded welded side and need 4 bearings on 
each point (16 per axis)

option 2: use two bearings on two flat sides and a third one on the "edge", 
some of the stuff has rounded edges (5mm radius).
i think you can run a bearing on this rounded edge....


how can i measure the quality of these rods?
how can i measure how precise the surface is and how straight they are?

any ideas appreciated

i will make a quick drawing to show you what i think of...
in the photos section soon... (i hope....)

regards
stefan