The builders of the DIY CNC routers overwhelmingly prefer MDF as the basis for these machines over plywood because they say that plywood is not as dimensionally stable as MDF. They claim the dimensional changes in plywood with weather and time would affect the accuracy of the machine.
I am toying with the idea of building one of these machines (haven't told LOML yet), and it seems to me that cabinet grade plywood would be as dimensional stable as MDF. My view is that MDF is better for flatness and surface integrity, but with all the glue and cross grains in plywood, its dimensional stability would be about the same. Since plywood is easier to join than MDF, and I have a lot of cabinet grade scraps leftover from a previous project, I would like to use plywood.
What do you think - is MDF significantly more stable dimensionally than plywood?