Shop-Built Fixtures Reveal the Magic of Switchable Permanent Magnets

Have you ever wondered how switchable magnets work? Not electromagnets, but those permanent magnet fixtures like the ones that hold dial indicators to machine tools, or the big, powerful chucks for surface grinders that can be mysteriously demagnetized at the flick of a lever. It seems like magic.

Thanks to [Andrew Klein] and this video on shop-built magnetic switches, the magic is gone. As it turns out, the ability to nullify the powerful magnetic field from a bunch of rare earth permanent magnets is as simple as bringing in another set of magnets to cancel out the magnetic fields of the first set.

[Andrew]’s magnetic pucks are formed from two thick plywood discs with magnets set into the edges. These magnets alternate in polarity around the discs, and they match up with mild steel pole pieces set into the face of the discs. The two discs swivel on a common axis; when the top disc is swiveled so that the polarity of the top and bottom magnets align, the magnet is switched on. Swiveling the top 60° puts the opposing fields in line with each other, canceling out the powerful combined pull of all the magnets and releasing the fixture.

[Andrew] sells a set of plans for the magswitches, which he built using standard woodshop tools. We think the design is perfect for a CNC router, though, where the fussy boring and counterboring operations might be a little easier. Perhaps even a 3D-printed version would be possible. This isn’t the first switchable magnet we’ve seen, of course, but we like this one because it’s all mechanical.

21 thoughts on “Shop-Built Fixtures Reveal the Magic of Switchable Permanent Magnets

    1. And well-chosen words worth a thousand pictures.

      A switchable magnet works by providing two alternate routes for the magnetic flux that have almost equal reluctance, so you need no force switch from one to the other. One path simply goes out through the face, and the other is shorted through the bar in the middle.

  1. Does posting a link to a video that seems to be intentionally vague to try to get you to buy his plans sort of go against the spirit of “hacking”? Kind of feels that way to me. That, and the guy comes across as kind of a jerk in the video comments.

    1. I dunno… I’d never heard of a switchable magnet until one of my co-workers showed me one a few weeks ago. It was completely enclosed, but it’s really easy enough to figure out just by holding it and moving the switch, you can feel how the mechanism works.

    2. Haking for the pure pleasure of hacking does not pay bills. So, here to us the new frontier of “i work a lot to do the video and I want to make money from my yob: youtube don’t pay enough, you don’t support me by patreon, but i have to take home some dimes”. So, he does a video make a nice “dancing cake” in front of us, we got the smell of it and it is delicious. But if we want to taste, we have to pay the slice. It is honest, noone force us to buy: after all, when you pass in front of a restaurant you can smell the food, but if you want to eat, you have to pay. The same here: he showed us the final product and some steps doing it. We can be smart enough to do a replica, but if we want the recipe, we have to pay. The time of “all for free, all well documented step by step by video and comments” are going to be the past.

      1. My comment was not against anyone trying to make a living. I just don’t know if it’s appropriate for Hackaday to drive traffic to a for-profit presentation. I don’t appreciate being “teased” by what is essentially an infomercial for plans that he likely modified from someone else’s design to begin with. I think that, like open-source software, if you’re going to try to make a profit by building on a freely-available design, you should be expected to share your modifications with the community as well.

        1. I think you completely missed the point of this post. Whether it acts as an ad for his product is irrelevant because by doing the video, he reveals exactly how switchable magnets work. Figuring out how stuff works is exactly what Hackaday is about, and if you care to reproduce this useful mechanism, you now have all the information you need to do so. If you choose to support the OP’s work by buying his plans, that’s your decision. Or if you decide the effort is not worth it at all and just buy a magswitch, then at least you now know how it works.

          1. I don’t believe I *did* “miss the point”. He teases and taunts and obfuscates in the comments because he doesn’t want to give away his “secret”. He even replies, “magic” to one person who asks how it works. That’s not what I like to see on Hackaday. In my experience, this site has always been about ferreting out and sharing information; not hiding it so people have to buy your stuff. There’s nothing particularly revolutionary about his design, if it even *is* his, and I really don’t care if he wants to peddle his plans. I just don’t feel that it aligns very well with the intent of this site. You are, of course, welcome to your own opinion.

  2. A few suggestions:
    * Start with a metal base plate to function as a flux return path.
    *Tap the plate and use a shoulder screw or stripper bolt for the center axis.
    *Omit the soft metal pins and press fit/glue the magnets in the holes parallel to the central axis using wood/plastic the same thickness as the magnets are long.
    *Simplify the index mechanism using two stop pins in the base and one radial pin in the rotating part.

    1. marketing is all about getting you to spend your money in one place instead of another. He wants you to build it from plans you purchase from him instead of buying a commercial product. Its actually clever marketing and i tip my hat to him for that. Especially given that by watching the movie and reading the article here and looking at his site, it should not be overly hard for anyone with the ability to make this for themselves should be able to come up with their own plans very easily.

      Originally i was going to just make a drawing of this and then post it in the open on the internet because i can and this article seemed more like an ad than a hack, but then i looked at his site and the video and was reminded of the saying: “a fool and his money are easily parted”. Or maybe some people just want to donate money to him so he can keep making videos and this is his way of providing such a route for cash flow.

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