Pickup Theory!

[Dolmetscher007]

I have some ideas that I'd like to play with, but I do not have a ton of cash to waste on just winging a lot of experiments. For example, I'd like to take an Alnico 2 bar magnet that is: 2-1/2" long, 1/2" wide, and 1/8" thick... and cut it into several 5/16" x 1/2" x 1/8" bars, carefully using a hacksaw. Imagine the magnet is a stick of butter, and I'd be cutting it into a bunch of "pats".

But as far as I can see, a bar magnet has a N pole and a S pole, and those poles are at the ends of the 2-1/2" length. So, if you cut it into... let's say... 10 pieces, would the 5 pieces that were on the N side of the bar, simply have a N polarity, and the 5 towards the S side all be south-oriented? That does not seem to be possible in my mind. Would each piece immediately "reorient" itself into a N/S magnet? If so, would the N/S poles be at each end of the bars, or along the 1/2" lengths? This is pretty hard to describe, but pretty easy to show. So, I drew up this rough idea and attached it to this post. The two N - S (one green and one red) is where I am wondering what happens to the poles when you cut off a "slice" of one side of a bar magnet? What happens to the poles?

[tedmich]

Cutting magnets (IME) only works in "thought experiments" so imagine whatever result you'd prefer

[LtKojak]

I have some ideas

What you just proposed simply doesn't happen, simply because of the laws of nature.

Seems you're getting more confused with every single question you ask.

Before you even attemp to break the 10-sec. 100m barrier, you need first to learn how to crawl.

[Helmholtz]

I have some ideas that I'd like to play with, but I do not have a ton of cash to waste on just winging a lot of experiments. For example, I'd like to take an Alnico 2 bar magnet that is: 2-1/2" long, 1/2" wide, and 1/8" thick... and cut it into several 5/16" x 1/2" x 1/8" bars, carefully using a hacksaw. Imagine the magnet is a stick of butter, and I'd be cutting it into a bunch of "pats".

But as far as I can see, a bar magnet has a N pole and a S pole, and those poles are at the ends of the 2-1/2" length. So, if you cut it into... let's say... 10 pieces, would the 5 pieces that were on the N side of the bar, simply have a N polarity, and the 5 towards the S side all be south-oriented? That does not seem to be possible in my mind. Would each piece immediately "reorient" itself into a N/S magnet? If so, would the N/S poles be at each end of the bars, or along the 1/2" lengths? This is pretty hard to describe, but pretty easy to show. So, I drew up this rough idea and attached it to this post. The two N - S (one green and one red) is where I am wondering what happens to the poles when you cut off a "slice" of one side of a bar magnet? What happens to the poles?

[ATTACH=CONFIG]51121[/ATTACH]

There are no magnetic monopoles, i.e. each piece must have an N and a S pole (generally every magnet must have equal numbers of N and S poles).
If the bar magnet is actually magnetized as shown in your drawing (which is not typical for HB magnets), you would get the result as shown in green.
But forget cutting alnico yourself. It's extremely hard and brittle. Manufacturers use diamond blades with watercooling and cut them in un/demagnetized state.

[big_teee]

I learned by taking cheap import pickups out of china made guitars.
I started with humbuckers, and most of them had ceramic magnets in them.
Since Alnico is such a hard material, it is not easily cut.
I've done some shortening on a few magnets, with fiber grinding wheels.
For overall pickup learning, I recommend buying a kit, and building it.
Whether it is a Single coil kit, or a humbucker kit.
Once you get that kit perfected, then move on to another type kit.
After you get that behind you, then try some of your own ideas.
If you have some old import pickups laying around, try rewinding them.
GL,
T
**Cutting the magnets like you suggest, is not practical.
For magnets like you show, use ready made rod magnets.

[Helmholtz]

Grinding alnico produces high local temperatures which may irreversibly degrade its magnetic properties at least in the parts exposed to the high temperature.

[big_teee]

Grinding alnico produces high local temperatures which may irreversibly degrade its magnetic properties at least in the parts exposed to the high temperature.

I've always heard that, but never found it to be the case.
Maybe I didn't get them that hot, and always recharged with NEO.
Also I've cut ceramic bass magnts off, but that is pretty tricky!
T

[Dolmetscher007]

There are no magnetic monopoles, i.e. each piece must have an N and a S pole (generally every magnet must have equal numbers of N and S poles).
If the bar magnet is actually magnetized as shown in your drawing (which is not typical for HB magnets), you would get the result as shown in green.

Vielen Dank Herr Helmholz! Ich habe fast zehn Jahre in München gelebt (gewohnt?). Ich vermisse die deutsche Sprache, und ihre Kultur!

Thanks for the info on magnet polarity. It makes sense that all permanent magnets must have a N and a S. I guess it is just hard to visualize, because, I think that if most people are honest... not very many people actually understand how a magnet works. It still seems like magic, really. It kind of blows my mind, I guess. If you have a 2 inch long bar magnet that has a N and a S pole, and you slap it onto your knee and break it into two 1 inch magnets, each of these two "new" magnets would suddenly have a N and a S too. That is crazy to me.

I have a question for you though, Mr. Helmholz... You said that humbucker bar magnets are not polarized the way I have it in my drawing. How are humbucker magnets polarized then? Are they like if you set one on a table, N would be facing up, and S would be facing the table? Or some other way?

[Helmholtz]

Vielen Dank Herr Helmholz! Ich habe fast zehn Jahre in München gelebt (gewohnt?). Ich vermisse die deutsche Sprache, und ihre Kultur!

Thanks for the info on magnet polarity. It makes sense that all permanent magnets must have a N and a S. I guess it is just hard to visualize, because, I think that if most people are honest... not very many people actually understand how a magnet works. It still seems like magic, really. It kind of blows my mind, I guess. If you have a 2 inch long bar magnet that has a N and a S pole, and you slap it onto your knee and break it into two 1 inch magnets, each of these two "new" magnets would suddenly have a N and a S too. That is crazy to me.

I have a question for you though, Mr. Helmholz... You said that humbucker bar magnets are not polarized the way I have it in my drawing. How are humbucker magnets polarized then? Are they like if you set one on a table, N would be facing up, and S would be facing the table? Or some other way?

Das ist aber eine Überraschung! Ich wohne/lebe tatsächlich auch am Rand von München. Es freut mich, dass es Ihnen/Dir hier gefallen hat.

The magnetization of the pieces of a permanent magnet is easy to understand, if you visualize the original magnet as homogeneously filled with tiny elementary magnets (actually spinning electrons) all aligned along the magnetization axis, i.e. all their north (and south) poles pointing in the same direction. Thus, if you cut the magnet, no realignment is necessary. The cut surfaces become new poles according to the (unchanged) orientation of the elementary magnets.
Outer poles are not produced by some magnetic charge at the pole faces, rather they are the summation effect of all the elementary dipols (magnets) inside pointing in the same direction, i.e. producing a directional magnetic field perpendicular to the pole surface.

HB magnets need to have their poles at the 2.5"x0.125" faces. You can find out using a compass.

[big_teee]

How a humbucker works!

Humbucker magnets are polarized on the long edge.
Like this diagram.

[Dolmetscher007]

Humbucker magnets are polarized on the long edge.
Like this diagram.

[ATTACH=CONFIG]51139[/ATTACH]

Ahhhh... okay... I thought that a humbucker was literally just two strat-style single coils, side by side. I did know that they were wound in opposing directions CW vs. CCW, and that one has a N polarity, and the other a S polarity.

But, according to that diagram, at least that particular humbucker, is not necessarily engineered that way. Instead of having two coils that have 6 pole pieces in the center of the coil, it has two "empty" coils, and a magnet in between the two coils. Or am I misinterpreting that diagram?

[Helmholtz]

Ahhhh... okay... I thought that a humbucker was literally just two strat-style single coils, side by side. I did know that they were wound in opposing directions CW vs. CCW, and that one has a N polarity, and the other a S polarity.

But, according to that diagram, at least that particular humbucker, is not necessarily engineered that way. Instead of having two coils that have 6 pole pieces in the center of the coil, it has two "empty" coils, and a magnet in between the two coils. Or am I misinterpreting that diagram?

Not shown in the drawing are the 6+6 mild steel pole pieces in the coils that attach to the magnet at the bottom and direct the magnetic field/flux to the top (strings facing) side.

[big_teee]

Here's the physical layout of a PAF type humbucker.

[Dolmetscher007]

Ahhh... ya know... I’ve seen diagrams like that one a billion times, but I guess it didn’t sink in until just now. Thanks man!
Not to just keep asking questions, but... why does one side have screws and the other fixed poles?

[Helmholtz]

Ahhh... ya know... I’ve seen diagrams like that one a billion times, but I guess it didn’t sink in until just now. Thanks man!
Not to just keep asking questions, but... why does one side have screws and the other fixed poles?

The height-adjustable screws allow to individually vary the magnetic field strength at the positions of the strings for improved signal balance between strings.