Ultrasonication done safely!


I’ve been making great progress on my woodwind project, and have found the Form 3 so accurate I can print the headjoints of these pennywhistles in one piece. However, the long, narrow slot (windway) directing the air towards the airblade always makes me a little suspicious when the occasional piece doesn’t sound quite right. I squirt IPA down the windways of course while washing, but perhaps 10 percent actually goes through and 90 percent backflows all over the room, so I wondered whether something that could really shake the uncured resin loose might prove more effective. The shop I used to work out of had a Form Wash, but frankly I thought it was more of a gimmick than anything else. I’ve never been impressed with the results versus just shaking the daylights out of the piece by hand in a bucket of IPA.

Now, a warning - generally speaking, ultrasonicating flammable liquids is exceptionally dangerous, and should only be done in a laboratory environment in equipment rated as, and this is the actual term, “explosion proof.” If you’re going to replicate my method, do so exactly as I describe, and at your own risk. This is only appropriate for small parts. If you can afford a Form 3 L you can afford an explosion proof ultrasonicating unit.

Anyway, from my research the main concern with ultrasonicating any high vapor pressure liquid is that, as you might expect, it generates a lot of vapor. Flammable vapors have a habit of finding ignition sources. Second, motion is essentially just heat. Move the shit out of something and you’re effectively heating it.

So, it logically follows that to do this safely, one should not allow vapors to be released, and should keep the IPA cool. This is as easy as putting your workpiece along with half a cup or so of IPA into a ziploc bag, squeezing all the air out, and submerging it in a consumer jewelry cleaner full of cold water. I have not tested this on industrial grade equipment, and again, if you can afford industrial grade equipment just get the right tool from the start. Just in case of any spills, do this under a fume hood, or as in my case in a small apartment, under the stove hood. Keep your CO2 fire extinguisher handy, less out of self-preservation and more out of a need for that deposit back should any shenanigans occur.

First, I wash the parts normally for five minutes in the first bucket, and five in the second. I then transfer the parts to the bag with some IPA from the second wash bucket, and sonicate them for about 30 seconds, four or five times, massaging the bag and flipping it between each 30-second run. Then, take the parts out, dump the IPA back in the wash bucket, and you’re done.

Now, danger signs would be feeling the bag and discovering it is warm, or observing the bag (which you have squeezed ALL the air out of) inflating with vapor. Abort immediately if this occurs.

I find this very effective for getting clean, consistent prints of parts with narrow openings without any hit to surface finish. Note that ultrasonicating for long periods does frost the surface as the cavitation bubbles start to eject partially-cured resin rather than just uncured resin, so if you’re after a nice surface finish, don’t exceed what I’ve detailed here.

The most recent batch of whistleheads played much better, much earlier in the voicing process and overall took much less hand-finishing to achieve the final result. I hope this is helpful for those printing functional and/or production parts with a need for precise dimensions. Six thou in the wrong place will absolutely kill one of these instruments, and Formlabs delivers in spades with the clear resin. I’m less impressed with the durability/accuracy of the color kit, but even with the color resin the results are pretty damn good.

As a side note, while I initially was using the clear resin just to prototype the heads, so many people at concerts and sessions asked for a clear one that I guess I’m making the production models clear by default!


There are water-based cleaners that are supposed to work as well as IPA, but aren’t volatile like IPA. I’ve never tried the stuff, but I’ve ready plenty of stories of people who have and were happy with the results.


Eh, I’d be suspicious of anything that doesn’t chemically dissolve the resin. There’s an industrial solvent that Formlabs recommends that is non-flammable and better still, non-surface-eroding, but it’s $300 a gallon, and if I’m going to pay $300 for a gallon of anything, it had better be single malt and come with a superb cask finish.


Like I said, I haven’t tried it. But I don’t remember ever reading a negative comment from someone who had.

I prefer my single malt peaty and at least 18 years old. And it better not come in a gallon-sized container. :slight_smile:


Or with a screw cap…