The box beam gantry configuration is the stiffest design. But having fought resonance before I do not want to do it again. Scared of those large thin sides of the box. And the 100kg weight of the model. So tried another iteration. This time its a simple "L" beam made of the three 3in x 3in 80/20 extrusions. Ran the math and while it is half the stiffness of the boxed beam it is still over twice as stiff as the original twin separated beam gantry design. Comparison deflection metric is 0.05mm. Going with this.

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Be back for more comments after getting this style gantry modeled.

Thanks,

John C