The torsional stiffness of I section is very poor compared to RHS or box section and clearly the ganty twisting directly leads to tool deflection (proportional to the extension of the Z-axis) parallel to the Y-axis. For the same mass you should be able to make a much stronger gantry with RHS, or an equally strong but much lighter gantry. The difficulty is the position of the Y-axis ballscrew is sub-optimal, but you should be able to get it close to between the rails. That's why people often use two pieces for the gantry with the ballscrew between. That also allows adjustment to get the rail mounting surfaces parallel.

Routercnc's spreadsheet posted a few years ago on this forums lets you compare the sections easily.

With this setup you'll be ok for anywoods really so long as your not expecting to cut 20mm in one pass.!!


I've done that in plywood...pretty scary at first but the second cutter survived!