There’s no getting away from it: routing with a CNC machine can cause lots of vibrations to travel into the work surface below, causing quite a bit of annoying noise too. To combat that I separate the machine from the work surface using 25mm thick firm sponge sheet: the blue non-flammable foam sold for furniture. It does an excellent job of isolating machine vibrations, but is really overkill for a small machine. So I decided to play around designing some flexible feet to fit onto the 2020-section aluminium frame that would do a similar job of preventing machine vibrations being transmitted to the hard work surface.
Obviously the best way of doing that would be to use a soft material that will wobble around: not enough though to flop down, and not so little that the rigidity transmits vibrations through it. As I’d recently bought some flexible TPU filament for my 3D printer, which is quite elastic, it seemed a good choice for making a squidgy wobbly thing (other flexible filaments may work well too). Designing a dampening system is obviously a rather complicated thing to do, probably best done by professionals using finite-element modelling and things like that. But that’s no reason not to have a go anyway!
For a DIY approach building a damper that flexes with the frequency of the vibrations, and preferably does that inefficiently, can be a good starting point. That way some of the job is also done simply because some vibrations will be cancelled out by others that are out of phase with them. So I went through a few iterations of small dampers so that I could squash them and get an idea of how rigid or squishy each design would be. It turns out that making squishy models at small scale using TPU isn’t as easy as you might expect: even with 10% infill density shells, creases and corners all increase rigidity too much. In the end I came up with the design below in OpenSCAD.
The design includes a flexible adapter at the top to squeeze into the slot in a standard 2020-section aluminium extrusion, as used on many cheap CNC machines. It’s the best design I’ve managed so far for a TPU damper just 20mm wide, and was designed to be printed without support material. It’s not floppy even though it has only 10% infill density, but has enough ‘squidginess’ to flex slightly under the weight of the CNC machine using a damper at each of the back corners and one under the middle front of the frame. If you want to have a go at printing your own, you can get all the files, including the STL file for 3D printing, by visiting the Thingiverse page.
The good thing is that this prototype allows vibrations to set up flexing in a variety of directions that can help prevent them being transmitted straight through to the surface below. Of course, I realise this is a work in progress, but the design does seem a useful starting point for some more experiments: perhaps tweaking the infill density and dimensions to start with so as to fine-tune flexibility while retaining the ability to support the CNC machine without bouncing around. And as a final note the design was easy to fit to a 2020-extrusion even though the slot ends were closed off: I’ve put a photo below to show what a finished and fitted damper looks like 🙂