On Mon, May 6, 2024 at 11:59 AM Chuck Guzis via cctalk < [email protected]> wrote:
> On 5/6/24 11:28, Wayne S via cctalk wrote: > > You do need a very strong magnet. I’ve put 3.5 floppies on top of a mag > tape demagnitizer ( not technically called that, but you know what i mean) > and it had no effect at all. I could still read them fine in my pc. I > surmised that the magnetic field generated was not strong enough to get > through the plastic disk shield. Gave up after that. > > I made my own PM demagnetizer (I do own a bulk videotape eraser also, > but this one is so convenient and works very well). The trick was to > use two magnets with like poles facing. I got the magnets from a > magnetron--it took a fair amount of clamping to get the things set in > place. Unlike poles facing doesn't work, BTW. > > https://i.imgur.com/MUKTExa.jpg > > --Chuck > At the old Alameda County Computer Resource Center (the non-profit computer recycler I was shacked up with before I got my own warehouse and started my own recycling operation), James ("God") designed a bulk demagnetizer that accommodated several hundred 3.5" floppies at a time. He'd run it for I think 20 minutes (the period of time he determined was required for 100% erasure of data), which also had the side effect of heating up the disks, which had the desirable side effect of making it much easier to peel off the labels. They sold bulk recycled 3.5" disks and made good money off it (this is late 1990s). I wish I could remember the details of how he made it, but he basically took some existing thing and either modded it in some way or simply re-purposed it from its intended purpose to conveniently demagnetize floppy disks. Sellam
