Magnetizing alnico rods

[Chris Turner]

I've got a question about magnetizing alnico rods...

Every time I've seen people post about the procedure, it seems that the best practice is to set up your strong neos that you're using to magnetize the rods in such a way that you can pass the rod a few times through the magnetic field, but not touch the neos themselves. Why is this?

Would the rod not be magnetized properly if you touch the neos with it?

[mr fab]

hi chris, I use a pair of N52 neos to charge my alnicos. in my experience, its not so much as contact with the neos that's the problem, but once they have stuck to the magnet face, getting them off the face of the magnet in a perpendicular direction is most difficult. in charging bar magnets, if you slide the magnet off the face of the magnet, (which is the easiest way to remove them) you can end up with magnets with uneven magnetisation across the face that was in contact, or even in some cases even a face partially magnetised in the opposite polarity. hence by not having them in contact avoids this problem.

I found this problem is particularly evident with alnico 3 bar magnets and also to some extent with alnico 2

the problem is less evident with rods as opposed to bar magnets, however I would be cautious

I have glued some plastic sheet on the face of the magnets and the magnets sit within the jaws of a small cast iron vice facing N-S. the vice allows me to adjust the gap between the two neos for the magnet to be charged , and I can leave my magnets in the jaws for a period to charge properly........ and I can open the jaws wider when needed allowing room to pull the magnet off one of the faces, in a perpendicular direction. as I said, I believe its the removal in a perpendicular fashion from the magnetizing face that is most important

hope this makes sense

[Chris Turner]

hi chris, I use a pair of N52 neos to charge my alnicos. in my experience, its not so much as contact with the neos that's the problem, but once they have stuck to the magnet face, getting them off the face of the magnet in a perpendicular direction is most difficult. in charging bar magnets, if you slide the magnet off the face of the magnet, (which is the easiest way to remove them) you can end up with magnets with uneven magnetisation across the face that was in contact, or even in some cases even a face partially magnetised in the opposite polarity. hence by not having them in contact avoids this problem.

I found this problem is particularly evident with alnico 3 bar magnets and also to some extent with alnico 2

the problem is less evident with rods as opposed to bar magnets, however I would be cautious

I have glued some plastic sheet on the face of the magnets and the magnets sit within the jaws of a small cast iron vice facing N-S. the vice allows me to adjust the gap between the two neos for the magnet to be charged , and I can leave my magnets in the jaws for a period to charge properly........ and I can open the jaws wider when needed allowing room to pull the magnet off one of the faces, in a perpendicular direction. as I said, I believe its the removal in a perpendicular fashion from the magnetizing face that is most important

hope this makes sense

That makes perfect sense. I had thought about the possibility of there being some weirdness as you pull them toward the edges of the neos, where the direction of the flux lines starts changing. I just also thought that coming in contact with the neos might be a no-no, but couldn't imagine why.

[David King]

A drill press or an arbor press makes a good way to pull the magnets straight apart without sliding them off the ends and ending of with an asymmetric charge. Whatever off balance charge you manage to achieve will probably migrate to an equilibrium in the first 24 hours.

[big_teee]

With rod magnets, I have a Neo glued to the file cabinet.
I stick the rod to it then contact the other end with the other Neo I have attached to a board.
I pull them off each magnet end several times.
The only problem with doing that it takes all the chrome finish off the NEOs.
My chrome finish is long gone.
Then I test them with the gauss meter.
Probably not the correct way, but It works for me.
T

[mr fab]

That makes perfect sense. I had thought about the possibility of there being some weirdness as you pull them toward the edges of the neos, where the direction of the flux lines starts changing. I just also thought that coming in contact with the neos might be a no-no, but couldn't imagine why.

I forgot to mention, that as a control I use one of those green magnet viewer cards. with a properly charged bar magnet, a horizontal line appears along the magnets length at the interface between north south. using this card I can check visually if the magnet is charged correctly as in some cases the line may be skewed to one pole indicating that I removed magnet incorrectly (those n52 neos have a lot of pulling force). those green cards are cheap and give a lot of handy visual info about the magnet. I keep it next to pickup winder and check every magnet before I assemble the pickup.