Hi Weijjmeister,

The double beam 'MechMate' style gantry is a difficult design especially if you want to exceed the performance of a well made standard gantry. Hats off for trying it.

The design in post 83 is very limited by the rail being mounted to a flat plate which is mostly cut away. Also, the overall gantry is effectively 2 'C' shapes. As each 'C' shape is joined to the other only at the ends then you've lost a lot of stiffness.

One of the other tricky areas is the bit you haven't drawn yet which is the Z axis and the options for joining it to the Y axis including fitting the Z ballscrew etc. The design will quite literally hinge on what you do there which is making it difficult for everyone to critique the whole thing.

If you study Jonathan's design you will see that the gantry creates 2 box sections (to resist the twisting forces that your 'C' shapes will not) which are joined by a single top and bottom panel. You will also see that the top and bottom panels, plus the sides which take the rail are about 20mm (?) thick, whereas the outer panels are more like 10mm. This is an economical use of material where it is needed.

I think that you would be better off starting from your earlier post (#70?), but mounting the rails onto the inner faces of the box section, but with a thick plate between the rail and box section. Or you could put the thick plate inside the box section so long as it spanned most of the height of the section. This is because with this layout the rails are being twisted off the frame (rather than pushed in or out on a conventional gantry), and the relatively thin wall of the box section may not be good enough.