cnc machine stiffness calculator

[Voicecoil]

You may be able to save a bit of time analyzing the components using this:

https://skyciv.com/free-moment-of-inertia-calculator/

It does shapes such as I beam, T beam and angle as well as tubes.

[routercnc]

You may be able to save a bit of time analyzing the components using this:

https://skyciv.com/free-moment-of-inertia-calculator/

It does shapes such as I beam, T beam and angle as well as tubes.

That's quite a handy calculator, so it might be all you need.


But if you want to know what it is doing, there are quite a few steps involved (which is why you are better making a spreadsheet if you want to do lots of them). I've shown a worked example which uses 2 rectangles in a T shape. You can make any shape using more rectangles but need to include more terms in each equation associated with each new rectangle.

The T shape is worked through in 7 steps:









Hope this helps.

[dn7]

New features in version 7 are:

• Stiffness approximations of commercial ali profiles (e.g. Hepco)*
• I value calculations for arbitrary shapes, not just RHS, round etc. This is a standalone calc and gives vertical bending deflection only.
• Gantry top bending in the X direction (previously ignored)
• Visual tool deflection error graph vs requirement

Usual disclaimers apply.

Hi routercnc,

the stiffness calculator looks incomplete. Is it still cooking on the back burner, or did you abandon it completely, lost interest? If so, it'd be sad because it's hard to explain how important I feel this tool is.

Regards,
DN

[routercnc]

Hi routercnc,

the stiffness calculator looks incomplete. Is it still cooking on the back burner, or did you abandon it completely, lost interest? If so, it'd be sad because it's hard to explain how important I feel this tool is.

Regards,
DN

I wrote this along time ago when I was designing my first machine to explore the importance of design choices. It got to a point where it worked well enough and would allow most users to gain some design principles for their own machine. I stopped there and have no plans to go further. For the next level of analysis with more complex shapes you need to step up to FEA but this works in a different way and needs commercially coded software to run. My advice would be to have a play and come away with some principles, such as material needs to be far away from the neutral axis to resist bending and torsion. But in the end the design still needs to be practical and buildable.