Damping Test of Concrete & Steel Tube

[Voicecoil]

I guess the resonance you need to damp in a machine tool isn't the ringing of the tube itself but of the structure formed by it. So if you were to stick a large mass (gantry, machine head etc) on the end of said tube and give it a knock, you'd get a much lower resonant frequency as the mass swung back and forth. That's the motion you'd need to damp in a machine tool isn't it? I expect the damping effect of that different structure at the lower frequency is likely to be different.

The tube resonance (or rather resonances) seems to be of some importance for the gantry at least on my machine, being a "raised sides" design, the long (y in my case) axis seems to be well constrained due to it's large attachment area to the base/bed with multiple fixing points and shows very little vibration even when properly thugging through metal. When the z-axis is in the middle of the gantry it will obviously load it and reduce the frequency of the fundamental resonance however it won't affect the 2nd harmonic much at all, similarly for other positions where it's sitting over a node. I found that damping out the higher harmonics with constrained layer damping was quite easy, the lower ones were less easy which is an issue to my mind as on typical sized machines they can fall into the same frequency range as cutter flute impact frequencies and low harmonics thereof.

[Tenson]

Thin Hollow


Thick Hollow


Thin Filled


Thick Filled

[Bongo]

This is all really fascinating, thanks for sharing! So I made an 8 x 4 machine frame from I beam profile filled with concrete mix (vid of it being made, concrete mix design details etc & it cutting: https://youtu.be/cqYJS27aC4w ) and wish I had made more video recordings of how the concrete changed the vibration characteristics. I actually used a vibration monitor on my smartphone, and had the data, but that phone got hit by a freak flying phone seeking branch when we cut a dead ash tree down :(

I suspect you have seen it, but I haven't seen mention of it here yet: Bamberg's "Principles of Rapid Machine Design" In it he describes a similar concrete-filled tube, but he adds constrained layer damping... Worth a look if you haven't seen it - page 96 on.