I had a discussion with another 'Zone member this morning and he was telling me about the problem he had with sag when his router was in the middle of his Y axis. I'm saving parts for a large table myself and have been thinking about this too.
The solution I'm thinking of trying is to attach a parabolic arch across the axis-something like a 1/8" thick by 1" wide steel strip with a 1" cube screwed to each end and drilled through.
A bracket on either upright would be slotted to accept the cube and a retaining pin would pass through the bracket, the cube, and the other side of the bracket. The arch would be a little under-curved, so that it would have to be bent into shape like a bow is when stringing it. This would ensure initial tension.
A length of small angle would bolt across the top of the Y-axis. The vertical portion would be drilled though every few inches. Bicycle spokes would be fed through these holes and up through corresponding holes in the arch. The same end pieces that are used on bike wheels would cap the spokes and allow tensioning.
This would be best suited for use on a very wide axis where the build material for the axis is extruded aluminum, like the 80-20 stuff. It should allow for a lightweight yet sag-free axis.
Thoughts / comments?
