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Thread: Magnetising and demagnetising tools.

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    Supporting Member tonyfoale's Avatar
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    Magnetising and demagnetising tools.

    There have been several posts here about tool demagnetisers, mostly using the mains 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.

    However, recently Mark Presling posted an ingenious demagnetiser which did not connect to any electrical supply, see here http://www.homemadetools.net/forum/d...ol-works-72881

    Today was my wife's birthday celebration and it was a big family day with much eating and drinking, which kept me out of the 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.

    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. This is shown following, with magnets glued in place. I made it with the magnets a little proud.

    Magnetising and demagnetising tools.-demag-01.jpg Magnetising and demagnetising tools.-demag-02.jpg Click images for full size versions.

    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 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.

    Magnetising and demagnetising tools.-demag03.jpg Magnetising and demagnetising tools.-demag-04.jpg
    The magnets can just be seen through the 1 mm Delrin cover.

    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 like this

    Magnetising and demagnetising tools.-demag-05.jpg Cleaning that off was dead easy.

    Here is the finished device shown working.

    Magnetising and demagnetising tools.-demag-06.jpg

    If I was making it 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.
    -------------
    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, and that's all there is to it. Thank goodness for modern magnets, years ago, if you needed to magnetise something, you would have to stroke the object many times with a magnet to build a significant effect. This current 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.

    Magnetising and demagnetising tools.-mag01.jpg



    PS. Since I took the photos I cut out a 1 mm thick steel circle to use as a keeper for the demagnetiser which completely kills any tendency to collect ferrous swarf

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    Last edited by tonyfoale; May 16, 2019 at 02:17 AM. Reason: Minor correction.

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    Thanks tonyfoale! We've added your Demagnetizer to our Miscellaneous category,
    as well as to your builder page: tonyfoale's Homemade Tools. Your receipt:




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    Thanks tonyfoale! We've added your Magnetizer to our Miscellaneous category,
    as well as to your builder page: tonyfoale's Homemade Tools. Your receipt:




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    Here are pix of the keeper for the demagnetiser.

    Magnetising and demagnetising tools.-demag-09.jpg Magnetising and demagnetising tools.-demag-10.jpg

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    Peter Sanders's Tools
    Hi Tony

    A magnet keeper spans both poles. In effect the screwdriver in the image shown is a keeper. A plate on each end of the magnet (not reaching the opposite pole) does not act as a keeper. The keeper shown in the demagnetiser does work as a keeper, as it connects the magnetic poles.

    When you state, "I just put it on the tool", do you mean to magnetise the tool, or to utilise the magnetism in the magnet (via the attached tool) JUST while the magnet is attached? I presume the former.

    The method of stroking the magnet along a tool such a screwdriver, is to align the grain structure of the metal being magnetised. I don't see how just placing the magnet on the tool does this same structural alignment (except of course while the magnet remains attached).

    Removing the magnet may leave a small residual magnetic attraction in the tool, but I doubt it will be as strong as the stroking method. Unfortunately I do not have similar magnets to try your idea. :-)

    Here is some info... https://en.wikipedia.org/wiki/Magnet_keeper

    I'd like to read your thoughts on this :-)

    Best regards

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    Quote Originally Posted by Peter Sanders View Post
    Hi Tony

    A magnet keeper spans both poles. In effect the screwdriver in the image shown is a keeper. A plate on each end of the magnet (not reaching the opposite pole) does not act as a keeper. The keeper shown in the demagnetiser does work as a keeper, as it connects the magnetic poles.
    Peter,
    You are quite correct. I called the end pieces keepers because that is what they were, they came with a bunch of magnets arranged in two columns and these end pieces bridged the two. I knew that keeper was not the right name in the context in which I used it but it was easy.

    Quote Originally Posted by Peter Sanders View Post
    When you state, "I just put it on the tool", do you mean to magnetise the tool, or to utilise the magnetism in the magnet (via the attached tool) JUST while the magnet is attached? I presume the former.
    I put it on the tool just to magnetise it, and removed it before using the tool.

    Quote Originally Posted by Peter Sanders View Post
    The method of stroking the magnet along a tool such a screwdriver, is to align the grain structure of the metal being magnetised. I don't see how just placing the magnet on the tool does this same structural alignment (except of course while the magnet remains attached).
    Stoking was a common technique when commonly available magnets were not very strong. Any field will do some alignment depending of the field strength.

    Quote Originally Posted by Peter Sanders View Post
    Removing the magnet may leave a small residual magnetic attraction in the tool, but I doubt it will be as strong as the stroking method.
    Getting the maximum possible residual magnetism in the tool is hardly the idea. Just enough to hold a screw on a driver or Allen key is all that is required. If stroking was necessary then we would not need tool demagnetisers because tools would never get magnetised in general use, but they do.
    If I wanted to maximise the effect I would not be stroking I would use a capacitor dump into a coil around the tool. In any case regardless of the strength of the magnetising field a given tool has a maximum that it will retain.

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    Supporting Member Toolmaker51's Avatar
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    Somehow missed mention of useful, effective RPM in vid and text. The speed to withdraw tool is apparent. Does the effect increase with more revolutions?
    Sincerely,
    Toolmaker51
    ...we'll learn more by wandering than searching...

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    Quote Originally Posted by Toolmaker51 View Post
    Somehow missed mention of useful, effective RPM in vid and text. The speed to withdraw tool is apparent. Does the effect increase with more revolutions?
    Good question and one that I asked myself. I have no idea of the answer though. I have used it in a lathe running at 500 rpm and in a drill press running at around 3000 rpm. Both seemed to work equally well, as it did when I withdrew as fast as possible (maybe around 0.5 sec) and when I took several seconds for the withdrawal.
    Withdrawing laterally worked and so did withdrawing axially.
    I use magnetic bars to hold some tools and that is probably the reason that some screw drivers get magnetised but I do not know how drill bits get magnetised but some do.
    I have some small electric motors laying around and I might just mount the rotor on one and keep it plugged in ready to go. It will only take up minimal bench or shelf space. That will have to wait though, this morning is dedicated to making a Renishaw style touch probe which will be a time saver when I use my mill as a poor man's CMM.

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    Quote Originally Posted by tonyfoale View Post
    <snip
    I use magnetic bars to hold some tools and that is probably the reason that some screw drivers get magnetised but I do not know how drill bits get magnetised but some do.
    I notice odd things collecting magnetic charges too. HSS or cobalt drill bits yes, HSS lathe bits, no, yet stored not 10' apart. Really bugs me when a full bar of cold-roll gets a charge. Sufficient chips adhere, each cut needs to be cleared so a stop hits solid material. PITA. Hot roll it occurs, doesn't seem to though. Being essentially identical steel, with different texture, stored on elevated rack just inches apart, what is going on?
    And yes from same location, and arrives same time. . .
    Sincerely,
    Toolmaker51
    ...we'll learn more by wandering than searching...

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    I found Tony's post only recently and it struck me that the easiest construction method would be with a 3D print. For people with a printer you can download a Fusion file and a STEP file from my blog.https://www.altrish.co.uk/2022/02/19...ymium-magnets/. The demagnetiser works a treat.

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