Tool Demagnetizer and Magnetizer




About: I like to race classic motorcycles and I make chassis and engine parts to enable that. As part of that activity I make tools and test equipment, both mechanical and electronic. I am the author of the book ...

Tools sometimes get magnetised, this can be both useful and undesirable depending on the type of tool and the actual job that you want to use it for. For example there are times when having a magnetised screw driver is helpful to hold a screw when you need to put it in an awkward place but unless you want to do that it can be a disadvantage because it will attract any ferrous swarf, nails and screws nearby. Drill bits are a tools which you would not want to ever be magnetised, it will get covered in chips when drilling ferrous material.

That said, we can see that a means to magnetise and demagnetise tools and other objects like vernier calipers would be a useful workshop addition. To magnetise a tool we only need subject it to a strong uni-directional magnetic field and to demagnetise we subject the object to an alternating magnetic field.

DIY tool demagnetisers, mostly use mains power in one form or another to get an alternating magnetic field. For many years I have used a modified transformer to both magnetise and demagnetise tools. It has worked well in each mode. I feed it with AC current for demagnetising and DC to create a magnetised tool.

However, recently Mark Presling posted an ingenious demagnetiser on the HomeMadeTools forum which did not connect to any electrical supply, see here

Yesterday was a big family celebration with much eating and drinking, which kept me out of my workshop most of the time. I got free around 20:00 and I went for a quick fix. As I did not have much time I wanted something that I could start and finish in an hour or so and Mark's device came to mind.


Step 1: Materials and Tools

As with most maker projects it is the idea that is important not so much the construction detail. A project can be replicated in many different ways depending on the materials and tools available to the individual maker, so the following is what I used with the tools that I have. Remember that you do not have to follow to the letter my own construction and there are different tools that could be used. Just take the ideas and run with it.


  • A piece of aluminium bar, mine was a small casting from the scrap box.
  • A 13 mm length of 50 mm Delrin bar.
  • Four rare earth button magnets, 12 mm diameter for the demagnetiser.
  • Two longer (25 mm) bar magnets or a stack of button magnets for the magnetiser. As shown above.
  • Tube of super glue.


  • Lathe, with turning and boring tools.
  • Milling machine, with 12 mm end mill for the magnet recesses.

Step 2: Demagnetiser

The principle behind this system is to make a device which presents to the tool, being demagnetised, an alternating magnetic field. This is achieved by rotating adjacent magnets of opposing polarity.

Any even number of magnets could be used and I chose four. Using more would require a larger diameter device to fit them in.

It did not take long to turn up a piece of scrap aluminium and mill 4 recesses for the magnets. The other side of the block was turned down to 13 mm diam. to fit in a drill press chuck to spin it. The large end was 41 mm diam and 11 mm thick, but these dimensions were dictated by the piece of aluminium at hand and are not critical. This is shown in the above photos, with magnets glued in place. I made it with the magnets a little proud.

Step 3: Plastic Cover

A quick test confirmed Mark's claims that it worked well. However, because the magnets were proud it gave a rough ride to any tool being demagnetised. I was also a little concerned that, in general use, the strong magnets would pluck ferrous swarf, nails, screws etc. from the surroundings, which would be hard to remove properly. To fix both I turned up a cover from some 50 mm Delrin bar which I glued in place. The face part was just over 1 mm thick. I had tested that a 3 mm gap between magnets and tool was close enough to work well so I knew that 1 mm would give no problems with the increased reluctance. The cover was also a safety feature in that it prevents the magnets from being knocked out and becoming missiles.

The magnets can be seen through the 1 mm thick face surface.

Step 4: Cover Tested Early

As it turned out the wisdom of covering the magnets for cleaning reasons became apparent very quickly. Within seconds of fitting the cover I dropped the piece and it rolled under the lathe and came out as shown.

It would have been a pain to clean off exposed magnets but was a simple chore with the cover in place.

Step 5: Using the Demagnetiser

This is simplicity itself.

I mount the device in a drill press chuck, although it could be anything that rotates and a milling machine or lathe are equally suitable. With the device spinning it is just a question of holding the tool, to be demagnetised, against the working face for a few seconds and then slowly withdrawing the tool. It will then be demagnetised.

The photos show a screw driver and pair of calipers being demagnetised. The calipers became magnetised when measuring the magnets used in this project.

Step 6: Magnetiser

Sometimes it is helpful to magnetise tools such as screw drivers etc. to hold screws and other hardware in hard to reach places. I simply feed my transformer based demagnetiser DC in order to do that.

In keeping with the idea of using a "no power required" device for demagnetising I wondered how easy it would be to make a magnetiser the same way. It turned out to be dead easy, it was also a no work device, I did not have to make anything. As the following shows I joined two longitudinally polarised magnets end to end and added a keeper to each end. Then I just put it on the tool, a screwdriver being the example shown, and that's all there is to it. This method does not impart as much magnet effect as my transformer method but quick tests showed that it should be quite adequate for most if not all needs.

Thank goodness for modern magnets, years ago, if you needed to magnetise something like a screwdriver, you would have to stroke the object many times with a magnet to build a significant effect.

PS. I later shaped the ends of the end pieces to fit better on the screwdriver and so reduce magnetic reluctance. This produced a noticeable greater magnetic effect in the tool.

Step 7: Conclusion

This Instructable demonstrates simple devices for magnetising and demagnetising a variety of workshop tools. Its simplicity and handy convenience guarantee that I'll be using this in preference to my old transformer based device.

If I was making it again with the benefit of hindsight, I would have made it all out of Delrin and milled the magnet holes deeper but inserting the magnets from the rear. It would not work any better but would be a nicer solution.

To finish off, I cut out a 1 mm thick steel circle to use as a keeper for the demagnetiser which "shorts" out the magnetic field and completely kills any tendency to collect ferrous swarf. Illustrated above.



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    17 Discussions


    9 days ago

    "As with most maker projects it is the idea that is important not so much the construction detail. A project can be replicated in many different ways depending on the materials and tools available to the individual maker"

    How true this is; I usually find that a lot of minutes on Youtube tutorials are wasted time for me since I don't have access to a lot of tools, and just the general idea of the project is enough to learn and get you going. Thanks!

    2 replies

    Reply 9 days ago

    I get very frustrated with those videos that waste so much time showing the same thing for too long. For example turning a large bar into a small bar on a lathe. You only need to see the first few seconds and the last few to know all there is.
    BTW I just looked at your post on the van conversion. I am thinking of doing similar so it was relevant. I,too, live in Spain and want to travel around it more than I have so far.
    You mention a problem with putting a vent in the water tank preventing the ability to pressure it. There is an easy solution to that. Put a simple one way valve in the vent. That will let air in to prevent a vacumn forming but will prevent air exiting under pressure.
    I imagine that the water in your rooftop pipe tank will get warm to hot, do you have a source of cold water on board?


    Reply 8 days ago

    Yes! In those videos de right arrow key on the keyboard comes really handy to skop 10 seconds at a time. -- Thanks for the tip on the one way valve, must try that this summer, although I've found that I don't really need to pressurize the tank. Water on the tap just gravity is OK. The water in the tank can get quite warm in the Spanish sun, although I wouldn't say it's too hot. I usually fill a water bottle that I keep inside for drinking, and it's great to have warm water on tap for either cooking or washing up. Hope you liked the Instructible, and good luck in your travels. By the way, I'm in Tarifa, Cádiz. Regards, Pedro


    9 days ago

    I've taken apart so many old hard drives that I won't run out of magnets for many years.

    1 reply

    10 days ago

    Learned something today - well a few things - about magnetizing and demagnetizing and m Weller soldering gun!


    10 days ago

    Nice idea! Unfortunately I don't have a lathe or a milling machine. Might try 3D printing the "housing" with counter sunk bolt for the shaft. Thanks for sharing Tony.

    2 replies

    Reply 10 days ago

    If you have a Drill Press and jig saw or coping saw you should be able to cut the plastic to (rough) shape, drill a hole in the center to fit an Aluminium, or Brass bolt four holes to accept the magnets. If you do not have plastic thick enough a maybe cut three (or four) circles and make a sandwich with the center hole drilled through all four and the magnet holes in the 'inside' two pieces. It is not essential, of course that the thing be circular (neither magnets nor tools give a damn), but you could 'chuck it up' in the drill press and sand it smooth and round (or use a rasp).


    Reply 10 days ago

    Let us know how you get on with it.

    WhiteWolf McBride

    10 days ago

    I thought of a much easier way to make this, without ANY milling. You look in the hobby section, and get one of those facing plates (flange couplings!) like you use on a lathe to turn a bowl, except hobbyists use them to attach wheels to axles. They come with holes in the face, so pick one that fits your needs. Then go to get some magnets that have a countersink mounting center-hole. Then attach the magnets to the faceplate using countersink bolts, using either nylock nuts or locktite on your nuts. Then put the right diameter shaft in the axle hole (I'd use an old drill bit) and Presto. Want a face-plate? Find a bottle or jar cap (plastic) and carefully find the center, and then fix it temporarily to the face. If its too thick, try another. Another option are the end-caps for rods and table legs, in plastic and rubber, in ~many~ sizes.

    And Presto - no special tools needed. A source of parts cheap? a certain online advertiser thats a 'bang' for the buck, and 'good' service (*I don't make anything off that*)


    10 days ago

    I have also used magnetized screwdrivers on occasion, and all I do is take one of the longitudinal magnets, and use its magnetism to attach it to the shaft of the screw driver lengthways. At the end of the job, remove the magnet. If the screw driver remains magnetized, then that cool demagnetizer would come in handy.


    10 days ago

    I don't have the lathe either so I just drag the magnetized tool through the tip area of my electric soldering gun (Weller), one of those that has the copper tip coming out of two metal rods. Always works.
    Unfortunately, no shop time involved, LOL