[EvilSpeeder]

I'm doing some machine improvements soon and I'm interested in finding out if my changes are effective. Machine vibrations in industrial settings are often recorded to monitor for problems and determine maintenance intervals. The best way to do this from what I understand is to use an accelerometer and a fast DAQ. I can't afford a DAQ, so I looked for alternatives. Out of curiously I thought I might be able to discover something purely through sound. You get really high sample rates, a wide spectrum of frequencies, and lots of available software for analysis. I used my iPhone and the standard voice memo app for recording. I placed my phone on several different places on the machine and ran the same g-code, recording each run. The program cuts a circle and descending depths in plywood. The software I used for analysis is Sonic Visualizer. The real value of this exercise will show when analyzing the recordings after the modifications, but these results were exciting enough that I decided to share.

I see several things going on. I can see the sound of the router motor itself. I'm running it pretty hard and you can see the frequency decrease as the load increases. I can see the sound from the stepper motors themselves probably mixed with the rack and pinion noise. I can see the vibrations due to the bit cutting through the material. There are a LOT of harmonics going on here, which isn't all that surprising just listening to it. I think I can really improve cut quality by reducing these.

This is an overall view of one circular cut. At the beginning you see the router freewheeling out of the cut, then slowing as it comes to full load. The opposite is seen on retraction.
Attachment 285692

This shows what I believe to be mechanical noise in the linear motion system. It's a DIY machine that's got a lot of hours on it and is due a rebuild.
Attachment 285694

Here are the sounds of the steppers/gears while going around the circle. There are some really interesting harmonics here. You can hear them, but it's really interesting to actually see them. I'm not sure what I'm seeing there. More investigation will tell.
Attachment 285696

My goals for this rebuild are to reduce mechanical vibration due to the linear motion system and reduce harmonics during the cut.

I plan to do more data collection to isolate out different sounds more clearly. If there is interest I will continue to post my results as well as annotating them in the future.

[shedbob]

I find this interesting.I dont think anyone has tried this before.Let us know what you learn.

You might find using an application with a spectrum analysis plot of frequency versus amplitude easier to analyse. As you will be able to see the fundamental frequency and the harmonics more easily.Your phone app may have this already.

If not and you have a pc near to the machine I would suggest this excellent donation ware.
Visual Analyser

You will need input transducers of course.You could try a mic or loudspeakers;large and small placed on the machine (they will have there own resonant frequency of course,but that can be found with a frequency sweep).A big speaker will have a lower frequency response but lack sensitivity,a preamp may be necessary.