"DeusEx"

[Jonathan]

The location of the supported rails on their side is unusual isn't it? Most of the ones I've seen seem to be in the Z; up/down axis usually one facing up and one facing down. Any reason for doing it that way?

Putting one up and one down evens up the load ratings. Clearly the supported rail bearings are weaker in one direction as that portion of the bearing is 'missing'. Sure I've mentioned this before, but nevermind. I calculated it once by measuring the angular position of each of the rows of bearings in a SBR25 block and from that calculated the relative force rating. The figures I ened up with for the SBR25 blocks was 980N (from datasheet) and -340N (calculated). So clearly if both rails are the same way you get 1960N in one X direction and only 680N in the other, however if they are opposite it's 1320N for both up and down, and even for X directions.

But... there's more to it than that. The round rails are connected to the aluminium support by a series of bolts into the rail from underneath. This connection isn't actually that strong (though clearly it's a whole lot better than nothing), so the rail will slill bend on the support with a force (if the beraings are mounted facing) parallel to X, or if the bearings are mounted on the same side they'll deflect with forces parallel to Z.
So it's debatable which is best...the force ratings above are a lot greater than what you will actually encounter, so perhaps deflection is more important because as the force increases the deflection will be greater. One day maybe I'll measure it.

Mocha take a look at Rogers build, this is similar to what you want to do, he told me he would have taken a more traditional approach if he were to do it again.

http://www.mycncuk.com/forums/showth...-5-Years-in%21

Interesting that he used a worm drive...

This is similar to what was thinking of doing, and may still do, for my machine. The difference is I also considered having two ballscrews on Y:

http://www.mycncuk.com/forums/showth...h-X-and-Y-axis

Adding a third rail would help, but when the two rails are profile rails I don't think it will make much difference, as long as what the rails are mounted on is strong, as they are rated for an equal load in all directions.