Author: Donald Papp / Source: Hackaday
An ultrasonic knife is a blade that vibrates a tiny amount at a high frequency, giving the knife edge minor superpowers. It gets used much like any other blade, but it becomes far easier to cut through troublesome materials like rubber or hard plastics. I was always curious about them, and recently made my own by modifying another tool.
It turns out that an ultrasonic scaling tool intended for dental use can fairly easily be turned into a nimble little ultrasonic cutter for fine detail work.
I originally started thinking about an ultrasonic knife to make removing supports from SLA 3D prints easier. SLA resin prints are made from a smooth, hard plastic and can sometimes require a veritable forest of supports. These supports are normally removed with flush cutters, or torn off if one doesn’t care about appearances, but sometimes the density of supports makes this process awkward, especially on small objects.
I imagined that an ultrasonic blade would make short work of these pesky supports, and for the most part, I was right! It won’t effortlessly cut through a forest of support bases like a hot knife through butter, but it certainly makes it easier to remove tricky supports from the model itself. Specifically, it excels at slicing through fine areas while preserving delicate features.
See It In Action
In the animation here you can see it slicing through some small supports on a tiny model. Cutting creates a puff of mist and particles, which a spritz of water helps control. The cutting edge of the tool shown is shaped like a chisel, which makes it easier to make smooth and clean cuts because the tip is very controllable.
The usual go-to method for removing supports is a good quality pair of flush cutters, but on very small models and in dense support areas they are neither maneuverable nor do they make it easy to see what one is doing.
Also, when cutting supports with normal tools there is always some amount of stress put on the piece that’s being cut. A knife forces its way through an object, and clippers shove anything between the blades apart which can crack or shatter small pieces. A fragile part can break from the force of these tools, no matter how careful one is.
The advantage of cutting with an ultrasonic knife is that very little force is transferred to the part being cut. Additionally, the small tool tip means it is highly maneuverable and easy to see what one is doing.
How It Was Made
We once featured an attempt to make an ultrasonic knife by harvesting parts from an ultrasonic cleaner. That project connected both a custom attachment and x-acto knife blade to the transducer. Results were mixed, and it appears that a critical aspect of an ultrasonic tool is to match the shape and mass of the head to the transducer itself so that they work…
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