[bcromwell]

Seem like a few high speed lathes and some mills are starting to use Linear Rails more often, so I started wonder which one is better or does each just have pro's and cons. Which one is higher in accuracy?

[in2steam]

Seem like a few high speed lathes and some mills are starting to use Linear Rails more often, so I started wonder which one is better or does each just have pro's and cons. Which one is higher in accuracy?

I think that depends almost entirely upon what the bearing you are using is, there literaly 1000 different ones. Just getting "linear bearing" off ebay and the such won't give you the right one. I am sure that a $xxxx bearing is better then a ground bed way if its designed for the proper stresses and loads. It also depends upon on the type of machine, if you are hogging a lot of metal in a roughing operation 9times out of 10 then you are IMHO better off with bed ways. Linear bearings are a pain in the rear when they need to be replaced, are not cheap, and need support compared to a plain surface.
Just my opinion
chris

[dpuch]

For commercial machines, the linear rails are used for lighter faster machines. The box (prismatic) ways are more rigid and usually used where there will be very high loads. Box ways are stiffer and larger contact areas, but higher friction. It is also a lot easier to make a linear rail machine. They do not need to be hand scraped.