Quote Originally Posted by Jonathan View Post
SBR20-400mm:0.03mm height variation.
Hiwin 15mm (760mm long): 0.06mm variation.
NSK 20mm (520mm long): 0.05mm variation.

The hiwin catalogue says +-0.1mm for normal precision height, but I don't think it states weather that is +-0.1mm for random rails, or +-0.1 over a single rail.
So what you checking here Height or straightness.? Very different things.!! Also did you fasten them down along there full length.? Doubt you did and untill you do then the height check means diddly squat.!

Also your not 100% wrong about bent being bent just 50% wrong.???

Profiled rail won't tolerate any bend if it's to work correctly but that doesn't mean they won't come with a very slight bend to them over there length.? Hense the ground edge's so it can be registerd against a reference edge.
They are designed to flex ever so slightly so they can be manipulated perfectly straight and also why you have fixed master rail and a floating rail that gets adjusted by moving the gantry of what ever the bearings are attached too slowly across the rails length while tightening the rails fixing bolts, so tweaking out any bend or tight spots.! This is also why most profiled rails have 60mm centres between the holes.

Now if round rail is bent then it's bent and your stuck with it without resorting to off machine straightening. Often thou it's not the rail it's self but the rubbish base that's bent or twisted and often not flat on the mounting surface.

Profiled and round are very different beast's so can't and shouldn't be compared they are not in the same league.