Monday 7 January 2019

How To Make a Small DIY Ultrasonic Knife

Some time ago I made a DIY ultrasonic knife. It's a small tool for fine detail work, and I use it for removing tricky supports from SLA 3D prints. I wrote an article about it that you can review for details.

The tool was made from a cheap ultrasonic dental scaling tool I bought from China. I sharpened one of the tips into a sharp chisel point. This knife edge vibrates a tiny amount at a high frequency, which gives the knife edge some mild superpowers. It's able to cut through hard plastic (like the supports of 3D prints from my Formlabs Form 2 SLA printer) with ease, without putting stress on the part being cut.

In the animation below, you can see my tool slice through the supports on a tiny piece that would not normally survive being cut by a utility knife or side cutters. The supports on Boba Fett's helmet-mounted rangefinger (I printed it at 25% size so it's much smaller than usual) are larger than the piece itself and would normally be too delicate to reliably remove supports, let alone leave a good surface finish.

One potential application that I have been made aware of for a tool like this is to post-process prints that are intended for casting jewelry. They often have fine details that must be preserved.

DIY Ultrasonic cutter removing supports from SLA 3D print. Note the puff of particles and water vapor when cutting.
The liquid droplets are water; I used a small spray bottle to help control the dust.
Note: the rangefinder is a separate piece in the original 3D model. I attached it for the express purpose of printing it as one piece and seeing if my ultrasonic cutter could handle removing the supports from such a small and delicate part, and it worked great!

If you'd like to know more, there's a video and additional details on The device turned out to be a handy addition to my toolbox, and wasn't particularly expensive. About $125 in parts and a bit of work to modify one of the steel tips, and I had what I needed.

If you'd like to try making your own, search eBay for "dental scaler" and "EMS Woodpecker" in the description. Buy one that has the correct plug for your country and you should be set for trying your own experiments.
UPDATE: Perhaps you have seen even cheaper handheld "ultrasonic dental scalers" for sale and have wondered whether they could be made to work. I bought one to find out. The answer is no.

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