New skew is magnetic from the factory

[Alpha-Dave]

Suggestions on demagnetisation please!

I received a Hamlet Alan Lacer large skew last week, and got to test it this weekend. To my suprise it is quite magnetic; not just a bit, but strong enough to jump into contact with the tool rest and make controlling the toe almost impossible.

It is strong enough to hold up a set of 80 mm jaws!

I'm sure that the normal demagnetisers for £3 from Maplins or a DIY shop will be pretty much useless for something this big (the cross section is 9.5x35 mm) as I don't think it could fit in the hole.

Can anyone suggest a way to demagnetise it for a reasonable cost? I'm against 'whack it against something hard' that I have read in old threads.

All suggestions appreciated, else I'll send it back next week.

 

[LancsRick]

Hit it with a hammer sharply a few times. Or run it close to a transformer.

 

[NazNomad]

I suppose heating it would be the answer ... However, I'd send it back as it's ''unfit for purpose''.

 

[Robbo3]

Wow!

+1 to NazNomad's reply

 

[NazNomad]

I'm wondering if it's been finished with a surface grinder and magnetic chuck?

 

[Alpha-Dave]

It had clearly been surface ground, but I would assume that the chissel grinds and the rolled edges were all done in a jig which may or may not have had magnets in. I have at least a dozen other Hamlet tools that are excellent and no hint of magnetism but most of them are ground from round bars, which I suspect would be held in a collet.

 

[Paul Hannaby]

Look on the bright side, it's a great place to store your chuck jaws! ;-)

 

[Alpha-Dave]

I called the shop today, apparently this is 'normal' and it should dissipate over time. The idea that I could send this one back and pay the difference on a more expensive chisel was turned down, at least until I had left it for a week on the lathe bed to see if the iron would draw the magnetism out. Apparently if I had wanted a magnetism-free chisel I (and all customers) should be willing to pay more for a demagnetising step, but as we don't specify that then this is what we get.

I'm quite disappointed with this outcome, but then I think I have got used to small companies offering a US-level of customer service, which some British companies just don't understand.

 

[Eric The Viking]

I don't think the lathe bed will achieve anything - magnetically soft iron is used to make magnet "keepers" across the poles of a traditional U-shaped magnet to preserve its magnetism.

Proper demagnetisers are hard to find nowadays, as we no longer use recording tape.

That said all you really need is a reasonably large electromagnet, or a coil. It doesn't have to connect to the mains, so you might dismantle a motor carefully so that you just have the stator (the outside coils) and not the rotor, and try connecting that to a modified old battery charger (they have overload cutouts and are only about 14V it ought to be quite safe). You need to remove the bridge rectifier (the thing with a lot of fins inside the case) and wire the transformer, through the cutout, straight to the output leads. If it has two charge rates, use the higher one. If not comfortable with this, don't attempt it!

You will need an assistant, probably. Put your chisel in the middle of the coils - you should feel it vibrating in the magnetic field. Leave it there for a few seconds, then slowly withdraw it to a distance of about 4-5 feet away. At that point switch off the coil (assistant's job?). "Slowly withdraw it" means take about 8-10 secs to move that distance, and go most slowly at the beginning.

Even if it doesn't do the whole job all at once, it will reduce the permanent magnetism of the chisel. Repeating the same process will further reduce it. The distance matters. If you just bung it in and then switch off after a few secs, it may end up more magnetised than before.

Obviously, this also works for keys, scissors, screwdrivers, etc.

E.

PS: If disconnecting the coil trips the overload cutout on the charger, this is a 'feature' of inductive loads, and shouldn't matter.

PPS: I have seen pocket demagnetisers for screwwdriver bits, etc. (Wera make one). I can't see how they'd be effective, without a coil driven by a chunky AC current source. If anyone knows or has experience, please say...

 

[Alpha-Dave]

Thank you Eric, that info is very much appreciated. Unfortunately I don't have an old electric motor to hand. I've had a quick look on ebay, and even 'spares or repair' motors start at £30 + postage. I'll check gumtree, or even call a scrap merchant to see if they have an old motor I can gut and return.

 

[Eric The Viking]

I wouldn't spend money on it - something small, like a broken extractor fan motor would probably do. It all comes down to how much flux you can get into the chisel to start with - you then reduce this to zero, which leaves it effectively demagnetised. To do it properly you need to start off by whanging it up to magnetic saturation point to start with, then progressively reducing the field. I doubt a motor coil will easily achieve this as-is, but it will have a demagnetising effect, so repeat-until-happy.

I'd drop in to see your local scrappie - they'll probably be happier face-to-face and a small dead motor should cost pennies. Skip diving where someone's doing a bathroom or kitchen refit should yield results too - people often sling fans rather than clean them. Yes, I am an old skinflint!

Heating it to the Curie point does the same thing, but you can't really do this if it's got a handle on it, and anyway, depending on the steel, it could well affect the hardening and/or temper. The coil thing might still be ineffective, but it's also nondestructive.

Note that the coil MUST be fed from low-ish voltage AC rather than DC (i.e. NOT from an unmodified battery charger!). If you use DC you'll get exactly the opposite result to what you want.

 

[Happy amateur]

Is it right that you should take what the shop said. If the tool is strongly magnetic then it is not fit for purpose as
fine control of the movement of the tool is essential. I have never had a turning tool that was magnetic and I don't
see why you should accept it as is
I wonder if trading standards would agree with the shop
Just my thoughts.

Fred

 

[Inspector]

Check to see if you have any nondestructive testing companies in your area that does magnetic particle inspection (MPI). The last step in crack checking steel is to demagnetize the parts. I doubt they would charge much if anything to demag your scraper. Many automotive engine rebuilders also have MPI machines for inspecting crankshafts etc. You could also check out the trade/vocational training schools. Crane inspection companies also do MPI and may be able to help too.

Pete

 

[Rhossydd]

Have you spoken to Hamlet themselves, rather than an intermediate dealer that might not want the trouble of an exchange/refund ?

 

[Eric The Viking]

I'm sure you're right, Fred, but there are a couple of reasons why we can't necessarily blame them:

1. It's quite easy to magnetise things in use or during the sharpening process. That said, I've never managed to magnetise anything strongly by sharpening, but I've magnetised a lot of screwdrivers accidentally, some quite severely. You can also sometimes do it by electric welding (irrelevant in this case).

2. It is possible that it got magnetised while being delivered. Trains in particular have large DC electric motors, and their fields leak. I'm sure we'll see a similar issue with hybrid cars Real Soon Now (tm), as they also use powerful DC motors.
. . .

For decades the BBC had a strict ban on recording tapes being carried on the tube, because of the risk of damage. I know of someone who spent an entire day trying to do just that - damage some tapes specially recorded for the experiment - trying different seats on different models of rolling stock. He didn't find a problem, but the conclusion was that the magnetic screening of tube train motors had been improved since the edict.

It's long been recognised that the earth's own field magnetises ships as they move. In WWII "degaussing" was invented, to alter a ship's field so that it didn't set off magnetic mines. Now called 'deperming' (usually), it is still done today:

The frame over the sub is a series of coils with _huge_ currents flowing in them.

The earth's field also upset colour CRT monitors and televisions, as the shadow mask just behind the screen became magnetised. Almost all of the later ones had degaussing coils fitted around the screen (behind the plastic), and automatically degaussed each time the power was switched on.

The earth's field is small, but the fact remains large magnetic fields are out there and will affect paramagnetic materials like steels (and tapes), some worse than others. So the shop may not have been negligent at all.

Pete (Inspector)'s advice above sounds very sensible - I bet they'd probably laugh and do it for free (or at least almost nothing).

E.

 

[woodpig]

Hit it with a hammer sharply a few times.

That would be my first choice.

 

[finneyb]

Screwfix have a demagnetiser £7 also there are cheaper on ebay http://www.screwfix.com/p/wiha-magnetis ... 0wod3WcIZg

Brian

 

[Alpha-Dave]

Thank you all for the helpful comments. I'll contact Hamlet directly tomorrow.

I always find that facts help support an argument, so I have tried to quantify how strong the pull is by using luggage scales and the tool rest.

Luggage scale set up at the point of balance on the ferrule. Perfect balance:


Scale zeroed:


First to test the magnetic adhesion between the spine and the tool rest.

400g force and it doesn't budge:


700g, still nothing:


1.05 kg before it breaks free!


Back to zero as the magnetic forces are released:


1.05 kg of adhesion from just this small contact area!


Now to test the wide sides; zero the scale.


This time over 1.6 kg required. I'm sure it briefly said 3kg, but the camera's shutter was too slow.

 

[Eric The Viking]

That _is_ quite impressive!

Hope you get it sorted.

E.

 

[mind_the_goat]

In the unlikely event that you have a decent old CRT monitor, they often had degaussing coils built in. Hold the skew up to the screen and switch it on (or they may be a button to do it on a monitor). Of course if it turns out there is no built in coil, you will just magnetise your screen too.