[mae-su]

Hi! I'm working on designing a router-style CNC machine (likely moving gantry) that can ideally cut aluminum. Rigidity is my main concern here, so I'm looking at different options on the X axis framing. The lower profile it is, the better. Yesterday, as I was using my school's laser cutter, I noticed it had some very interesting looking extrusions that made up the gantry. I know that laser cutters aren't subject to the same forces as machines with spindles, but this extrusion feels very rigid compared to others. It's a BossLaser LS-2440, and I've attached a picture of the extrusion below. Does anyone have a hunch on what type of extrusion this may be? Is it custom?

Thanks,
Mae

[jaguar36]

Might just be me, but I don't see any pictures attached.

Regardless, the rigidity of an extrusion is going to be directly related to its area moment of inertia, which can be calculated fairly easily.

[joeavaerage]

Hi,
for a given external dimension, say 100mm x 50mm, the section that yields the highest second moment of area is a tube, be it rectangular or circular.
The features like grooves and flanges inside the boundary of the section add to the area but not neccesarily add significantly to the second moment of area, and maximizing the stiffness
is all about the second moment of area and the Youngs modulus of the material.

The Youngs modulus of aluminum is 70GPa whereas steel is 205GPa. Thus for a section of a given second moment of area steel will be 205 / 70= 2.93 times stiffer.

The bottom line is that a steel rectangular or square section the same size as your aluminum extrusion is likely to be much MUCH stiffer.

Craig