Magnetizing and demagnetizing screwdrivers and screws

Andreas Thaler

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Small screws that you can drive directly into hard-to-reach places with a screwdriver.

An indispensable work aid.



And a screwdriver can be magnetized quickly, for example, with a tool like the one in the picture on the left, which can also demagnetize screwdrivers. However, if the screw itself is already magnetized, this cancels out the effect.

On the right, you can see a choke for demagnetizing tape heads in magnetic tape recorders. However, its magnetic field is too weak for metal parts, at least that's what my tests have shown.

What are your recommendations for demagnetizing screws and screwdrivers?
 

tjwspm

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I use exactly the same tool (the red one on the left).

I use a magnetized screwdriver to position very small screws that I can no longer position with my finger when screwing them in. A very useful tool.
 
OP
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Andreas Thaler

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There are demagnetizers that run on mains power. Does anyone use them, and what are their experiences with them?

And how can I demagnetize screws?
 

bernard_L

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De-magnetizing works by going around the hysteresis loop while progressively decreasing the excursion. In other words, submit the magnetic material to an alternating magnetic field, while decreasing the amplitude to zero. This could be done with a solenoid powered by 50Hz AC, and either decreasing gradually the excitation to zero, or withdrawing the screwdriver from the solenoid.
Disclaimer: that is from university physics; a working device would require some experimenting and optimization.

Also: do not let a magnetized screwdriver come close to shutter (or aperture) blades
 

Bushcat

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Wowza, that's not a cheap thing. my degausser currently costs around USD 15. To paraphrase Bernard, I go "around the hysteresis loop while progressively decreasing the excursion" simply by lifting the wand away from the target(s).
 

eli griggs

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This is a tool I should use, but for several years, I've just used 'doughnut' shaped magnets saved on several Wiha, Wera, Vessel, tiny screwdrivers in my kit and can't complain but I might be having issues I simply don't see.

By the way, Amazon has this Hex set + one cross point for a good price(it seems to me).

 

Kino

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Yes, this how I used t degausse the CRT on my Hazeltine Motion Picture Color Analyzer to realign the color guns for purity.

You can see several videos on YouTube where people are using a large degaussing coil on a CRT.

Tip: never turn on or off a degaussing coil near anything electronic that isn't the thing you are degaussing. If you start, you must finish the entire routine, or turning off the coil at close distances will collapse the field and do the opposite of what you intended!

Tip #2: Leave your wallet, any watches and your phone in the NEXT ROOM when running a large degaussing coil. Ask me how I know...
 

BobUK

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We are lucky having an a.c. mains supply here.

My first demagnetiser , and probably the safest, used a door bell transformer to lower the domestic 240 V ac down to 6v ac.
This was connected to a homemade coil of fine wire wrapped around a piece of plastic tubing.
To use it, the power is switched on, and the screwdriver to be demagnetised is slowly inserted into the coil along the central axis of the coil.
The screwdriver can be felt vibrating with the rapidly reversing magnetic poles.
It is held still in the magnetic field for a bout 30 seconds then slowly withdrawn from the coil along the axis of the coil and magnetic field. When well clear the power is switched off.
Keep watches well away from the demagnetiser when in use. Both quartz and mechanical watches can be damaged when place near demagnetisers.

I have made a few over the years including a massive one I wound myself that can take a medium sized drill vice.
I am ultra careful when using that as it goes straight across the domestic 240 vac.



WARNING 240 volts ac can be lethal, so unless you really know what you are dealing with, leave well alone.
 

Chan Tran

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For screw drivers I used a DC solenoid coil from a solenoid valve to magnetize it. I power the coil, insert the screw drive in the hole and cut the power abruptly. That would magnetize it. For demagnetizing i use a coild from an AC solenoid valve. Power the coil with the screw driver in the hole then withdraw the screw driver slowly.
 

BobUK

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I have just remembered a demagnetiser I read about in a few vintage watch repair books.

Not long too ago a fair number of premises here had no electricity supply, gas lighting etc.

The device recommended back then was to use one of those hand cranked grinding wheels, that had the cranking speed increased with a gear arrangement.
Instead of a grindstone, a bar magnet was attached on the revolving shaft.
The device was set in motion with the item to be demagnetised held close to the revolving magnet.
The rapid change in magnetic pole orientation acted as a demagnetiser.
I would't like to catch my knuckles on the magnet when going full tilt.
I have never seen or tried one, but the idea appeared in several old repair books.
Possibly ideal if you live off the grid.
 

reddesert

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This is how a commercial powered degausser works. They were once used to quickly erase magnetic tapes (which IIRC could be re-used), and are used to erase magnetic hard drives for security (which can't then be reused).

I found a youtube video where someone examined an unpowered magnetizer/demagnetizer like the red Wiha one in Andreas's first post. It just has two permanent magnets on either side of the magnetize slot. They are aligned to enhance the B-field lines along the magnetize slot. When you draw the screwdriver through the magnetize slot, along the field lines, it gets magnetized. The field lines are more perpendicular to the de-magnetize slot, so I guess the idea is that drawing the screwdriver through the de-magnetize slot semi-scrambles any previous magnetization. The stairsteps in the de-magnetize slot are just plastic and have no function, other than allowing you to tell the slots apart.

I just magnetize screwdrivers lightly by drawing them along a strong permanent magnet, like the back of a loudspeaker, or a magnet taken from a hard drive.
 

eli griggs

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Just saw earlier, Harbor Freight has a key chain demagnetizer, $5.
 
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