Since the day I got access to the waterjet, the main question in my mind was "What would it sound like to cut through something while recording it?". So I recorded a few things being cut.
And it was AWESOME.
But then I was like "I wonder what the cutting itself sounds like."
And I still had access to the waterjet, and I had some extra contact mics I'd wired up.
This is the story of the end of those contact mics.
Step 1: Preparing and Mounting the Contact Mics
Obviously I'm not going to throw my nice JrF's in the waterjet for destruction. In fact, I'm not gonna throw anything that costs more than a buck in there for something as silly as this. So, I just made my own balanced pair out of some extra cable and a few piezo sensors, following the Balanced Piezo Mic Instructable. Pretty simple, and it works!
I mounted 2 mics, one on each side, to a scrap piece of 1/4" mild steel. I put one on each side just to see the differences in sound of the waterjet cutting directly through the mic versus cutting through material and the mic. I blue-taped them to the metal, which worked well enough.
I hooked both mics into my Sound Device 722, which is so overkill for this it's not even funny, but if I'm gonna take silly sounds, it should be well recorded, well preamp'd silly sounds.
Step 2: Making the Cut
The cut was literally just a straight line, right through the mics. Nothing too complicated about it. You can watch it happen in the video above.
One issue that arose was my improper clamping of the workpiece. Near the end, you can see that I didn't make sure to clamp over the slats on the bed, so there was pressure exerted by the clamps that caused the workpiece to pop up. This could've meant some very expensive nozzle damage, but I got VERY lucky this time.
Remember kids: Always triple check your work holding.
Step 3: The Results
And there it is. 2 mics, cut in half. What'd it sound like?
The mic cuts happen at about 0:20 (for the mic on the far side of the metal from the nozzle) and 1:30 (for the mic on the close side of the metal to the nozzle). If you're not a fan of noise music, this probably isn't all that great, but personally I love the textures of sound that the waterjet puts out (and why yes, I do like Merzbow, why do you ask?).
Not to mention, how brutally awesome is using 50,000 lbs pressure behind garnet pellets and water to make noise, eh?