Some thoughts on cnc machine design principles. . .

[williamturner1]

By popular demand I've updated the spreadsheet to include a range of sections for the gantry sides in bending.

As expected the channel is similar to the I beam for torsion (i.e poor), but redeems itself in the bending load case.

Great work! Thanks for sharing.

I really am surprised at the figures for IBeam. With industrial stock ... eg 100mm Width / 200mm Height / 10mm thickness upper + lower plates, 7mm thickness of upright.
Comparing it to 12mm thick Plate, 200mm height
and RHS 120 x 80 x 3

Ive placed 120x80x3 2m length between two RSJs and stood on its middle and bounced, observing its considerable flex.
I've done the same with a 2.2m RSJ (100x200x10) and done my best tigger impression but observed little if any movement.

but the spreadsheet indicates the opposite should be observed:
DEFLECTION: 31micros vs 2micros (RSJ vs RHS)
TORSIONAL STIFFNESS: 28,000 vs 1,800,000 (RSJ vs RHS)