To round out this discussion I did a box gantry also. Deflection of 0.02mm is the lowest yet.

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Dimensions of the boxed beam are the same as the widest dimension of the horizontal "L" gantry.

So all this playing around with FEA has basically validated the advice given in the sticky threads at the top of the sub forum. That is, use a box or an "L" beam. I think I will. Just gotta decide which one to chose.

Thanks to all.

John C