Bearing Spacing on Y-Gantry-Carriage

[Jonathan]

The force on each bearing block is inversely proportional to the spacing, so increasing the spacing of the top two blocks reduces the force on each. The deflection of each bearing relative to the rail is proportional to the applied force (common sense), hence increasing the spacing reduces the deflection and you end up with a more rigid assembly. The formulas to explain this can be found in this document by Hiwin. Also it should be noted that there's a limit to how far you should increase the spacing since there becomes a point where the gain is smaller than the deflection caused by the material they're mounted on bending in between the bearing blocks. You're not approaching that though, so it's fine. When I make my new gantry the Y-axis bearings will be about 450mm apart, but there will be 3 on each rail...

If anything I think the forces on the lower blocks would be greater since they are closer to the tool, so it would be wise to space them out further too, however clearly that doesn't fit well with the rest of the design.

I hope you are adding plates to the sides to stiffen the joint between the aluminium extrusion and X bearing mounts.