Sharpening with Bluetooth

Few things are as frustrating in the kitchen as a dull knife. [Becky] and her chef friend collaborated to build a Bluetooth module to tell you when you are sharpening a knife at the optimum angle. That might sound a little specialized, but the problem boils down to one that is common enough in a lot of situations: how do you tell your exact orientation while in motion? That is, with the knife moving rapidly back and forth over the sharpening stone, how can you measure the angle of the blade reliably?

Looking for a challenge, [Becky’s] first attempt was to just use an accelerometer. It worked, but it wasn’t very precise. Her final answer turned out to be a full inertial measurement unit — the BNO055 — that combines an accelerometer, a magnetometer, and a gyroscope along with enough smarts to fuse the data into actual position data.

The project should be simple to replicate. It’s made of off-the-shelf modules, breakout boards, and common components like a battery, a switch, and some magnets. There’s also a 3D printed case to cover it all up.

Of course, another answer is to make a jig to hold the knife at the right angle. If you aren’t a fan of sharpening knives by hand, we can help with that, too.

20 thoughts on “Sharpening with Bluetooth

        1. I actually have a use for this. I have a nice sharpening kit but it only works with standard blades. Anything odd can’t be sharpened accurately. With this bad boy, I can slap it on whatever has an edge (a hatchet/axe?) and just let it guide me to the right angle.

          1. You can save yourself some money and use the same trick the USFS does when setting an axe edge, cut an edge gauge out of some brass sheet or cardboard at your preferred angle. 30-35* works for general use on axes, hatches, and chisels.just check it against the edge frequently until the profile is set.
            Unless the edge is really dinged up or misshapen from previous sharpening attempts you should be able to just match the angle already there. Permanent marker or dykem along the edge will help you see where you’re taking metal off. Consistency is more important than matching an exact angle unless you’re making metal lathe tools or gravers.

    1. Close to the end of the video, [Becky] says that the purpose of the device is to develop muscle memory and a correct form while sharpening, so that with practice the device will no longer be necessary.

    2. Since there’s no quick and functional feedback mechanism it’s a very hard skill to get good effective practice at. There’s a reason many people switch to ceramic-post sharpeners where the knife just needs to held straight vertical to get a consistent angle.

      1. Those V block ‘sharpeners’ are horrendous. If your life is really so busy you can’t learn a new skill, buy one of the sharpeners that hold everything in a jig (Lansky makes an affordable) at a fixed angle.
        People have hand sharpened all manner of edged implements for millennia it’s not that hard.
        You just have to pay attention to what you’re doing and not rush things.

    1. I bought a knife sharpener from Ali with this exact same principle, brandname “ruixin”.
      It works much better than you would expect from the pictures.
      Quality of the stones also seem to be good. The stones do wear maybe a bit fast, but that is much better than a stone loosing it’s sharpness and just sliding over the knife. These stones keep their bite.
      My motivation for buying the Ruixin was from a demonstration of some american brand knife sarpener on youtube of the same principle, It probably was better quality, but for a redicilous price of USD300 or so.
      The Ruixin has amazing capabilities for it’s USD 30 pricepoint.
      Some other Chinese sharpeners have very bad quality stones and are not worth their shipping cost.

  1. IF this will do anything for getting rid of knives being “sharpened” to closely resemble a metalworking (cold) chisel.
    Nothing like asking a knife to slice tomatoes and you’re handed something (that they mention paying $48 for)that has that high angle on it like a bolt cutter.
    Keep the included angle at no more than 30~35 degrees max.
    You’ll find that slicing succulents, fresh peppers, onions, a steak etc, becomes something close to fun!

  2. The true hack would be dedicating the time and practice to learn how to sharpen knives without any special equipment. I guess that falls under the category of a body hack these days.

  3. Why does this need bluetooth? Why can’t there just be a bunch of led like a guitar tuner? middle light lit you are at the right angle left or right leds lit and you are at the wrong angle. Seems a bit over engineered.

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