An interesting experiment on stiffness and damping

Over on mycncuk (sorry, external) there’s an interesting thread where one of their forum members tests out the vibration damping and resonance characteristics of steel tube vs. steel tube with concrete damping (bringing different moduli and loss coefficients together as per this post with the excellent graph)

There’s actual data with waterfall plots of the decay times for both the rigid steel and the damped steel tube which are quite revealing in terms of the machine behaviour. Having seen a little data the choices of people like Hermle to use epoxy granite in their machines in addition to steel become quite a lot clearer.

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Isn’t it really the drive, gantry and spindle/mount that primarily limit CNC router performance? Solid granite tables are required when doing things like laser holography, but likely orders of magnitude overkill for CNC routers.

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Yep,

The Shapeoko is primarily limited by V wheels, and drive belts but lots of folks upgrade those.

The linked post is about the extrusions and other long components and how their movement below and above resonance relates to both their youngs modulus and loss coefficient. What’s interesting in those results is the amplitude and persistence of excitement at the resonant frequencies (and multiples) and how bigger, thicker metal doesn’t necessarily do what we might expect.

It’s frequently assumed that stiffening and reducing vibration are synonymous. In many cases rigidity and mass are seen as the right ways to fight vibration and that’s not the whole truth. There are folks here who’ve done linear rail type upgrades but who have also filled their extrusions with things, including pea gravel, which exhibit some of this high loss coefficient damping characteristic. The waterfall plots in the linked test are an interesting data point in understanding the outcomes of stiffening vs. reducing vibration and particularly in how mixed materials provide options for tuning this.

It’s also interesting to consider what damping characteristics those Gates belts exhibit in comparison to a rigid system.

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My Nomad with ballscrews and higher axis tq compared to the shapeoko, cannot take as aggressive a cut and is much more susceptible to resonance. The Shapeoko also is sand filled.

Its pretty interesting how the style of cutting can differ. I’m thinking the Nomad could benefit from stepper dampers.

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That sounds like a good experiment…

Blast this forum. 30 minutes gone learning about stepper dampers.

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You get into silicone fluid viscous or rattlers?

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