First Proper CNC Router

[diycnc]

I have persevered with the shimming approach, and after a couple of evening measuring then shimming, both my Y and Z axis are planer to within 0.05mm.
Measurements are 100% repeatable too, and I have no reason to believe the method has any error at all. For example, after adding a 0.1mm shim to under a bolt, the measurement increases by pretty much exactly 0.1mm at that location.

Only slight tweak to the method is I now do the leveling of the measurements in excel, rather then physically moving the surface plate.

Iv tried to solve the amount of support under the rails issue by adding more bolt, lots more bolt! I have 50mm spacing between bolts now, rather than 150mm as they arrived.

I initially started aiming for a 0.25mm deviation over the Y-axis but blew past that on the first attempt, so just did 1 more iteration to see how good I could get it, and ended up at 0.05mm deviation from a flat plane. It was almost 3mm when I started.
At the moment I reckon the play in the cheep bearings, and maybe even the deflection of the frame under the gantry weight will be more than this, so its total overkill!

Shims are just small pieces of aluminum sheet, cans, and foil. Nothing special.

Im pretty chuffed with the results, it's one of the few things that's gone better than expected.
I painted the frame too, blue Hammerite spray paint, and the paint is so soft I can scratch it off with my fingernail! I clearly didn't do a very good job of cleaning it before painting.


Any suggestions for how to measure straightness of these round rails?