I was wondering if you considered using a thin kerf ripping blade (fewer teeth) when making that deep cut. I would think that the fewer teeth and deeper gullets would produce a lot less burning. Also, if you clap on a taller fence, you will have a much easier and safer time keeping that board at a perfect 90.

When cleaning a sawblade, I’ve found a little steel wool highly effective. An acid brush? Why make it harder than it needs to be?
Green stuff? Dumb. Leave your blade in a caustic for an indefinite period? If you’re that dumb, you deserve what you get. Use something that works, is cheap and requires a reasonably intelligent person.

Sincerely,

Robert H. Galloway

RMN: I think we agree that a powered-down drive is much safer in the presence of a magnetic field. What I’m trying to point out is that the drive is a complicated system with a lot of amplifying power, and trying to say “this will never cause a problem” is overconfident.

I talked with a few architects here at work (major HDD design center) to see what experience they’ve had with external magnetic fields in customer environments. While I can’t disclose what they said, they each had worked on specific failures that were caused by external small-scale magnetic fields. The common theme was interactions that are less-than-intuitive.

To erase the data on your hard drive, the magnet would need to generate a field strength (in gauss) higher than the platters’ coercivity (in oersted). Most modern hard drive platters have coercivities well above 3000 Oe (4000 for “perpendicular recording” drives), and the _surface_ field of NIB magnets is generaly well below 2000 gauss, so you could theoretically put the magnet directly _onto_ the hard drive platter and still not erase it. Of course, to do that you’d have to open the drive so it would probably be dead anyway, unless you happen to be in a clean room. :-)

Of course, if you put one of these…

http://www.engconcepts.net/Lis.....agnets.asp

…on your drive, there’s a good chance it won’t survive. But I have a feeling Marc isn’t using those for the gadget station. ;-)

But actually here’s a thought: how about incorporating some really strong magnets into some piece to make a part of it “float”? That would be cool.

Note: All the above applies to hard drives that are turned _off_. If the hard drive is working, the magnet can cause the heads to move, and that can corrupt the data (because the electromagnet on the head _is_ strong enough to change the platters, obviously, or you wouldn’t be able to write any data to it).

- Magnets can cause damage to a hard drive. If you want to know why the ones inside the drive are OK, I can elaborate in the Coffee House on the forums.

- Given the strength of these magnets and the distance from the electronics, you should be OK. Two inches or so would be a good safety margin for all your electronic devices. If your magnets line up with the walls or bottom of the cabinet, I’d call it good.

Great episode -really coming together.

Mike

Unless we’re talking about insanely powerful magnets or degaussers (like the ones actually designed to erase drives), you can pretty much put them ON the hard drive and they won’t do a thing, especially if the drive isn’t spinning (if it is spinning they may arguably lead to some oscillation which can lead to damage).

There are very strong magnets INSIDE every hard drive (lots of people buy damaged HDs just to get those magnets), so if simple proximity to one caused any damage to the data, no hard drive in the world would work.

Basically, to damage your hard drive without being placed directly on the platters, a magnet would have to be strong enough to hurt you if your hand got caught between it and the hard drive.

Now, even relatively small and weak magnets can cause some things like LCD screens, speakers or touch sensors to malfunction, but those will generally be temporary problems. Moving a magnet along a wire can also interfere with the signals being transmitted.

I wouldn’t put any electronic gadget too close to a strong magnet (too close meaning less than 1 or 2 inches) just to avoid magnetising any part of it (gadget LCDs are bad enough without warped colours), but the hard drive itself is the least of your worries.