I was thinking about how sometimes when I have a sketchy setup, I can almost completely cure harmonics just by clamping an adorable little vice clamp (that weighs less than my phone) to the part.
But also, the circuit board in your phone isn’t glued to the case (probably). You’ll in part be measuring some or all resonant modes of the circuit board within the phone.
Here’s what I bought; $10 for 3 boards:
I’d expect that regardless of the source of accelerometer data, you would plan to take the scalar (dot) product of the three axes at every sample and do an FFT on the resulting waveform, and have samples across the range of spindle speeds you care about?
Yeah, it’s loading each individual flute that I think is the problem, unless you have a really bad spindle, which is its own problem… And a transducer will let you control the input consistently so you know what you are testing more reliably.
Honestly, you could start by just testing ringing from whacking it with a solenoid! The main reason to test it with a transducer is to look for resonant frequencies, but a 4’ length of tube won’t tell you anything about the resonant frequencies in your final frame. The clearest signal about damping vibrations will be a single shot. The main reason to whack it with a solenoid and not a hammer is repeatability. Come to think of it, you could set up a fixture to swing a hammer a fixed distance to get that repeatability and it’s probably just as good, or maybe even better, since getting a solenoid that can whack it hard enough might be a pain.
You would still take the scalar product, but no need for an FFT, just load it up in audacity (e.g.) and measure something consistent. Maybe the number of cycles for the amplitude to drop by 10x, or log(x), or something — I don’t know that you care whether you are directly measuring a time constant, probably more that you can compare them between samples.
(Incidentally, If I were trying to do this using analog sensors, I’d put a voice coil on X and Y, ignore Z (defining that as the length of the bar), use an op amp configured as a summing amplifier, and then look at the waveform on a DSO. But that seems like a lot more work!)
Well, that was the idea where I saw it mentioned in a comment on the epoxy
granite garnet video I linked to on Social… But if you are also testing oil-soaked sand, you could test oil-soaked cast iron swarf I guess?