ok, first attempt using sketchup 8

[deannos]

Although it's convenient to use RSJ on X and Y, you'd be better off using a different cross section. The torsional stiffness of RSJ is pathetic, hardly much better than a sheet, so especially on the gantry where the cutting forces will tend to twist the beam you would get a lot of deflection. Similarly RSJ is poor under shear stress, which is the case on the X-axis. To an extent you have compensated for that by using a large thickness, but with less material you could use box section and get much greater stiffness.

Ok, would i be better using Ali extrusion, or are you talking about steel box section. What size would you suggest

One reason not to use smaller RSJ is it reduces the vertical spacing of the Y-axis bearings, which is something you want to maximise.

I'm still confused on the axis direction, by "Y" are you referring to the bearings the longer gantry is riding on

I want to get it right the first time, or as best as can be


How do you use the multi quote option, i clicked it and nothing happens