Re: Bulk erase methods

In article <pan.2005.07.13.22.18.03.757605@xxxxxxxxxxx>,
Rich Grise <richgrise@xxxxxxxxxxx> wrote:

> On Wed, 13 Jul 2005 16:57:58 +0000, Guy Macon wrote:
>
> >
> >
> >
> > Naveed wrote:
> >>
> >>"Guy Macon" <_see.web.page_@xxxxxxxxxxxxxxxxxx> wrote...
> >>>
> >>> Barry Lennox wrote:
> >>> >
> >>> >On 11 Jul 2005 15:45:50 -0700, bigcat@xxxxxxxxxxx wrote:
> >>> >
> >>> >>What methods can be used to bulk erase a lot of floppies? I dont have
> >>> >>one of those nice big electromagnets, and was wondering if anything
> >>> >>else to hand could be used. I presume 2 seconds in a microwave with a
> >>> >>load to prevent sparking is too risky, though I should try one.
> >>> >>
> >>> >>Cant think of anything else that causes a strong enough mag field...
> >>> >>any ideas?
> >>> >
> >>> >Old magnetron magnets will do the job very nicely.
> >>>
> >>> Magnets do indeed destroy data, but if that's all he wants to do
> >>> a bonfire is even better. If he wants to re-use the floppies he
> >>> would be better off with something that creates an alternating
> >>> magnetic field.
> >>
> >>If the magnet was attached to a drill running at low speed then that would
> >>cause an alternating magnetic field.
> >
> > Excellent point.
> >
> > Which brings up the question, what is the optimal frequency?
> > With an electromagnet you get 50/60 Hz unless you go to a lot
> > of effort to get another frequency - and it works well - but
> > with a motor/magnet it's easy to pick a frequency.
>
> The frequency is irrelevant. The point is to have a strong enough
> magnetic field to line up all of the little magnetic thingies in
> the media, and then turn them all around on the next half-cycle.
>
> A permanent magnet will line up all the little thingies, but then
> you've got a magnet bias that could introduce confounding factors
> when re-using the media.
>
> Anyway, with the AC field (hey, there's a usage of AC that we
> didn't consider in the "Tastes Great-Less Filling" ACDC thing!),
> just twirl the magnet fast enough that it can sweep the field
> over the media once or twice.
>
> Then, the secret is, slowly move the moving magnet ( or half
> a transformer, or whatever) away from the media, and as the
> alternating field gets weaker and weaker, reversing fewer
> and fewer thingies, until on the average, there's no
> residual magnetism in the media.
>
> It's the same principle with CRT degaussers, but they use
> a PTC thermistor in series with the coil. Press the degausser
> button on your monitor - see the pretty patterns? And how
> they decay? That's the principle that ends up with
> negligible residual magnetization. I know there's a whole
> nother jargon here, but, come on! :-)
>
> Anyway, Hope This Helps!
>
> Cheers!
> Rich
>
>

Years ago, bulk magnetic tape erasers were sold for erasing reel-to-reel
magnetic tapes. You might be able to find one in an antiques store ;-)
and use it for your purpose.

Al
.