I recently ordered a Onefinity Journeyman CNC router. The table dimensions for this monstrosity are 72"x52".

The top will be 3/4" sanded plywood, everything else will be pressure treated kiln dried 4x4s. A 32"x48" MDF spoilboard will go on top of the table, and the CNC will add about 200lbs as well.

Rigidity and squarness are the major factors here. I'm concerned the table will dip in the middle and be a problem. Twisting forces would be bad for the CNC; bending one of the rails would be like a $1500 to $3000 loss. In order to combat this I'm putting a stretcher across the middle of the top, and 2 additional legs.

I have some (very expensive) steel braces in my amazon shopping cart but I would rather use joinery to make the corners.

* What joint is recommended for the corners where 3 4x4"s come together at right angles?

* What joint where the stretcher meets the center legs?

* Should I change from 4x4s to 2x4s for everything but the legs?

Thanks for any advice!!