(posted on yahoo too)

I have tried and tried to sucessfully build the slides for a flying gantry router, but with no joy.

I seem to be unable to get all eight bearings on the block assembly to keep in contact with guide rods over the whole travel.
An error of 0.5mm can magnify to several mm over the whole travel. This problem is compounded by the fact that this alignment error happens on two axes.

Am I missing something? Has anyone successfully build a slide, and if so, how did you overcome these problems. If you pre-loaded the blocks, how did you do this and with what materials?
I also noticed that MDF warps when glues are used.

I may have to return to the original design as it seems to address all these kind alignment problems...
Question is can I create one using 12mm guide rods, and where can I get the 12mm brass bearings ?

Geoff.