Strength and stiffness are two different things. Stiffness is the more important in this application.
I've been too busy to read much in the last few weeks, or I would have posted more in this thread.
If you haven't seen it, you may want to read through my very long thread on building a large wood construction router.
My 68" gantry beam will be an MDF torsion box, roughly 8"x8", and 68" long. To make it stiffer, the MDF panels are laminations of 1/4" MDF.
Calculations using Beamboy show a deflection of about .001" with a 200 lb load on it.
Anywhere on my machine where I will be attaching metal to wood, I epoxy phenolic plates to the wood, and machine it flat. This minimizes the wood compressing when bolting metal parts down. It also gives me perfectly flat and straight surfaces for mounting the linear rails to.
Of course, it's much easier to do this when you have access to a large industrial CNC router.
Here's a link to my parts for my beam, which I cut many years ago. I should be starting assembly this winter, once I get the garage in my new house organized.
https://www.cnczone.com/forums/cnc-w...ml#post1168468