Why not use unsupported rails?

[JAZZCNC]

The accuracy of a profile rail is not much different to a round rail -

Sorry Jonathan that's Rubbish total utter rubbish they don't compare in any way.!

Just the fact the bearing blocks are ground flat and true on profile bearings makes a massive difference. Bearing in mind 90% of round rail is cheap chineses tuff I've yet to see a round rail bearing block that's flat on top with sides machined 90deg. Only the very best brand quality are any where near and these can cost the same as profiled.

Then we get to the actual bearing it's self, the round rail bearings are sloppy from the begining just use a dial gauge and apply side pressure to see that, you won't find this on profiled bearings due to preloading and the precision machining of the rail.

They are night and day apart.!!