Hi Jonathan,

Glad to see the spreadsheet being used. I think they could still do with making even more user friendly. They're ok if you are used to doing this stuff and just want to save doing it by hand, but if this is new territory then you could easily be put off, or worse still, try to use them in the wrong way and get meaningless answers.

Your method of mixing materials by scaling Young's modulus has got me thinking . . . think it's OK.

Your estimate of stiffness increase for supported rails over unsupported (2.8 to 6.8 times better) neglects the part that the supported rail is bolted to (often a thick plate for Z axis), which is the main reason for doing it. You'll find if you factor in the mounting plate that the differences are significantly greater still. Good work though at 1 in the morning!

Other CAD s/ware, such as AutoCAD, CATIA will give properties including second moment of area, so for complex shapes this is another way to do it.