Hard Drive Magnets in a Pickup- created 07-18-2010
Peterson, Alan - 07/18/2010.17:10:21
I Gots Me a Dremel and I'm Not Afraid to Use It
I'm not ready to give this a try as of yet - lots of other projects are stacked up on the bench right now - but I'd like to attempt creating a pickup made from a magnet removed from a blown computer hard drive. These things are
Problems I face include the odd shape of the magnet itself which makes it hard to mount and align; and the location of the poles are still something of a mystery to me (doing the compass trick, I'm getting some oddly false readings). But this strong a field might make this magnet a natural for a low-Z PU, where I'm losing out on hundreds of windings.
I have a stack of dead hard drives in the garage - not enough to make that windmill generator I'm seeing in my head - but more than enough to noodle with guitar pickups for awhile. You'll know I'm underway with my magnet experiments when the aurora borealis shifts locations to just over Washington DC.
Keep us posted.
And when I hang it on the wall, I'll always know which way is North
Of course, they will work, as far as getting a sound out, but I think that with magnets that strong you would have to keep them fairly far away from the strings. Even with alnico magnets, which are FAR weaker than hard drive magnets, you have to keep them a certain distance away from the strings or the magnetic field interferes with the string. They can even pull a string out of tune, kill your sustain, and cause the world to fall off it's axis. Well, not that last one.
But of course, the only real way to find out for sure is to try it. Let us know.
Is magnet strength a problem that needs to be solved
It's not necessarily a problem, but it's certainly a factor. Originally, pickup magnets weren't of the highest quality, and as they aged, they lose a bit of power. Some people like the tone, though, which is why those are popular among those folks.
They then came up with alnico, which found it's way into speakers and pickups. It has a longer magnetic life, losing far less than the older magnets do. It is also a fairly strong magnet. I suspect that it's about this time that adjustment started really being an issue. With stronger magnets, putting the pole pieces too close to the strings puts them in the area that they pull the strings magnetically. This is what leads to poor tone, lack of sustain, inability to tune properly or stay in tune, etc, and the only way to deal with it is to move the pole pieces further away from the strings. So you lose volume because of that.
My question would be whether you have to move the pickups so far away from the strings as to negate any signal strength you would get by having such strong magnets. It's a very interesting question, and I am looking forward to hearing what happens.
Another issue is going to be that those magnets are a really odd shape, kind of a 6th of a circle, usually glued to a mounting bracket. They are screamingly strong, though, and it's certainly possible to machine them into something usable (I would think, though I'm not an expert on this by any means).
It is an interesting question. I hope we hear the outcome of it, sometime soon.
I've been using Neodymium magnets in my pickups for about 10 years now. The issue with these large and strange shaped magnets would be the bulk of them. If I had to use them I would follow the style used on those old National pickups like the one in this photo.
<a href="http://s67.photobucket.com/albums/h300/searcystringworks/Pickups/?action=view¤t=3-21-096.jpg" target="_blank"><img src="http://i67.photobucket.com/albums/h300/searcystringworks/Pickups/3-21-096.jpg" border="0" alt="Photobucket"></a>
This allows you to position the magnet away from the coils by using a steel pole frame to transmit the magnetic charge through the coil and to the strings.
I have never tried and I am not a machinist either, but I don't think that you can machine those magnets, as they are neodymium.
Didn't someone in the $100 Tele contest make pickups like this? I think it was the guy who salvaged all of his parts from a copier.
I could be wrong and often am; respond accordingly.
You can't cut these magnets. The shatter easy and lose their charge if they are heated above their maximum operating temperature, which is 176°F (80°C) for standard N grades
Also, the dust can explode
You can buy these magnets cheaply at some arts and crafts stores like Hobby Lobby. I have a couple packages of them in 1/4" disks waiting to be used in pickups. Well the label says they are 1/4" but they look closer to 5/16" to me, or maybe they're a metric size. I plan have steel pole pieces on the pickups and them mount the magnets below the windings like on a pickup with ceramic magnets
"Also, the dust can explode. "
OOH, sounds like an episode of Mythbusters! So the dust is potentially dangerous, but the magnets themselves are safe? How interesting. Well, I don't think I'll be taking any of them to the band saw, then. Thanks for the safety tip. That's not one that you would ordinarily think of.
Please keep going on this. I would love to hear how it turns out
You can get all manners of shapes and sizes of neo magnets here:
<a href="http://www.kjmagnetics.com/" >K&J Magnetics</a>
Like Clint said, you are best using the magnet to charge some steel poles. That will keep the pull at the poles at a sane level, e.g., using neo rod magnets in a Fender style pickup would really be too strong.
Here's a book to look into for some off the wall ideas:
"Getting a Bigger Sound - Pickups and Microphones for your Musical Instrument" by Bart Hopkin with Robert Cain and Jason Lollar.
Amazon's got it, and so do a number of other booksellers.
"... using the magnet to charge some steel poles" I'm assuming we mean carbon steel not stainless (non magnetic)
Correct
So now how to ignite the magnet dust...
I have to admit a certain fascination with that, myself. Now, if we can only get Kari from Mythbusters to explain it to us, I'll be fascinated for at least an hour at a time.
Seriously, though, would it be a spark, or would it be a pressure issue? I can't imagine what would make a multiple metal like that become explosive.
All sorts of metals and alloys are incendiary and/or explosive. Thermite is a nice famous one, a mix of iron oxide and copper oxide
Good point, I hadn't thought of that. But all of them need some sort of ignition source or a sudden force change to set them off. Some pure metals react with water dramatically.
So the question is what is the method of combustion for the dust cut from a rare earth magnet?
Some metals in very thin shavings, lathe swarf, powder, or granular form, oxidize rapidly in air and will self-combust. A surprising one is titanium, which is benign in solid form and is "sticky" to machine--it doesn't like to let go of itself. But titanium lathe swarf will combust and burns with a hot, almost transparent blue flame.
The ones that don't spontaneously combust from the heat of oxidation can often be triggered, like corn starch or powdered sugar, by a spark or open flame. I think neodymium is one of the latter.
I used to make thermite with iron oxide and aluminum dust. Get it burning with a magnesium ribbon fuse, and the iron oxide's oxygen moves to the aluminum. It produces a lot of heat. You get molten iron and little black grains of aluminum oxide. They used to use it to repair cracked railroad rails--pack it into the break, light it, step back. After it cools, file or grind off the lumpy parts.
I've seen an aluminum bale of turnings combust from being tainted with magnesium turnings and being encased in a plastic bag. I can tell you I removed the entire stack it sat atop at unsafe speeds on a forklift due to proximity to titanium bales.
When I heard about the magnets combustibility I instantly had an irrational desire to fire it through a tube wrapped as a coil in order to record the explosion till I got a perfectly balanced recording. Then I would just blow the **** out of stuff and try to figure out uses for blowing micro magnetic debris all over kingdom come.
Grind off the lumpy parts
Hahaha! Bill, may I suggest you use that as your new "2nd line of information", replacing
>I'm assuming we mean carbon steel not stainless (non magnetic).
Certain grades of stainless are indeed magnetic. Gibson claims to use it on one of their pickups, and I've used it at one time, but didn't like the tone on the particular pickup I was making.
Check some stainless flatware (knives, forks, etc.). Most of it is magnetic.
It's true some stainless will mag as they are "martensitic" and contain less chromium, moly and nickel and more carbon than "austenitic" which is more corrosion resistant. Most stainless you commonly run into is austenitic 300 series stuff and most of that in flat sheet stock. Martensitic stainless is aimed more at machinable applications and solid strength than corrosion resistance. Most likely to find slug material here. Dunno why you'd use it as there are much more magnet responsive metals. Perhaps they have a tighter control of the field and can use overly strong magnets on the cheap. Just a guess
Joe Brown in the UK ... gettin' it done with hard drive magnets:
http://www.joebrown.org.uk/wp/?p=1476
As I understand it, neodymium is fairly easy to ignite with a saw or grinder, and it burns not unlike magnesium. Like magnesium, it also seems that hot neodymium reacts violently with water, turning some of it into hydrogen. Thus, a neodymium fire cannot be extinguished with water. It seems it also reacts violently with CO2, so you can't use a CO2-based fire extinguisher either. The fumes from burnt neodymium are highly toxic.
The stuff also corrodes at an incredible rate if exposed to air. Any neo magnets available are plated, usually with nickel. According to Wikipedia, a centimeter-sized uncoated magnet would completely oxidize within a year. If you machine it, you must find a way to completely seal it.