[How-To] Make a powerful permanent magnet

[Cadillac]

Anyone out there a magnet guru? I want to take the plunge into magnet fishing. I have a 10yr old son that loves the outdoors. We go fishing all the time and it’s good times but if you e every fished with a 10 yr old it doesn’t last long. Fishing on the boat is better he stays focused on fishing. When we shore fish that’s a whole different story. If the fish arnt bitting he gets bored really quick and starts tossing rocks. Messes up my game.
So I thought let’s try magnet fishing. He can throw till his arm falls off. He loves finding stuff. So it might be win win for both of us.
While searching the web I see they will spec like 1000lb combined lifting force. Which the magnet is a hockey puck size with a thin magnet on each side of the large surface glued to a metal frame. So they have two 500* mags back to back. To me that’s a 500* lifting mag from each side not a 1000* mag.
Can you combine mags to make a stronger magnet? I want to make a 360 degree magnet with a great pulling and holding force. Does anyone know of how to get the best holding forces without spending hundreds on some crazy big neodymium magnet?

 

[Jake M]

What are you hoping to find? These are great at picking up lost hand tools and such. They're from Harbor Freight, so when they say 250 pounds, they mean more like one fifty, or one seventy five... But dead flat on solid metal, (yeah, I know, that's an ideal you're not likely to hit when you're trolling with a magnet....) this will do 200 pounds. I wouldn't put my foot under whatever that thing is.... But it'll do it. All you need is a rope if you want to test the waters before you jump in...

250 lb. Pull Retrieving Magnet

Amazing deals on this 250Lb Pull Retrieving Magnet at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

That said...... There is some serious black magic that can be done with magnets. Magnetic fields follow things, transfer through things, can be combined, cancelled, re-routed in different directions, and generally played with in a lot of unexpected ways. It's kind of fascinating, but it's not something I've ever pursued, so I can't offer you advice on how to build one, if that's the route you go.

 

[Cadillac]

I have a magnet very similar to that. I’ve tried it and it doesn’t work very good. Neodymium is the best mag available I just wonder if theirs a way to compound the force of multiple magnets?

 

[Inferno]

I know a tiny bit about magnets.
I only have a few thousand of them in my house.

The magnet ratings you see in the adverts are misleading. They're NdFeB magnets with a N-rating over 50. The trick is the metal that surrounds the magnet. I might be wrong but I suspect it's mumetal or something that's designed to act as mumetal.
Basically, the magnet properties of mumetal will reroute magnetic fields. People think it blocks magnetism but it merely redirects it.
If you take the 500lb magnet you will find it has a magnetic pull on only the face. That's because the metal surrounding it is rerouting the field to the face.
So, while it has a pulling force of 500 pounds, the pull of the actual magnet, minus the housing is much less.

These fishing magnets aren't a new technology. I had a 500lb magnet in 1980. It wasn't NdFeB (neodymuim Iron Boron) but it so it was much larger. Although the pulling force was 500lbs, the entire magnet had to be in contact with the surface of the metal to lift that much.
So while I could actually lift an anvil with it (I did), I couldn't lift most items that weighed 50 pounds.

The new fishing magnets have a smaller surface area so it's easier for them to find a good surface to get the most magnetic contact.

Also good to note that the housing around the magnet on a fishing magnet helps to protect the magnet itself. They are very brittle. I've exploded many by letting them get out of my grip when joining them. I have some pretty powerful ones but nothing too extreme. I pinch my skin but will never lose a finger.

 

[ChazzC]

Go here, K&J Magnetics is a great resource, and the respond to questions.

 

[whitmore]

A permanent magnet, of whatever type, has an 'output' of flux, measured in Webers; the
field strength is Webers/square meter... or some equivalent. What determines the lift capability,
is the fact that this field is NOT uniform, but gets weaker with distance: the force
with which the magnet lifts iron is proportional to the field strength gradient, not the field
strength.

You can use pole pieces and supermagnets to make a lifting element for big steel chunks
by putting two poles at a big steel spacing, or to hold a map on a sheet steel surface by
using multiple poles close together (2mm is typical) in stripes, like on those rubbery magnet
things we all have on the refrigerator...

The rubbery stripe things have all the gradient in the 2mm region near those close poles; they
hold as well to a thin sheet as they do to a big block.

A horseshoe shape is actually not a bad compromise in a lifting magnet, you can choose the gap
between two soft-steel poles, and hide a NdFeB supermagnet somewhere it won't get slammed (they're
expensive, and somewhat brittle). Just remember the poles conduct that flux, connect one
to the N and one to the S face of the magnet, and go fishing.

 

[homebrewed]

I suspect it's mumetal or something that's designed to act as mumetal.

No, it's not mu-metal, permalloy or the like. They have very high permeability -- in other words, they are excellent "conductors" for magnetic fields -- but only for relatively weak magnetic fields. The technical term is that they have a low Bsat, the magnetic-saturation point. Once the magnetic field exceeds Bsat the magnetic field is no longer confined to the metal, so there is less magnetic flux that can contribute to the attractive force. Here's more information along those lines <pun>.

The ideal material for a lifting magnet is one that has both high permeability and a high Bsat. It turns out that it's same stuff used to make iron-core transformers. However, for a DC application like a lifter you won't need a laminated core, that's used to reduce eddy current losses in an AC application.

 

[talvare]

What I know about magnets wouldn't fill a teaspoon, but I'm curious about why you want to use such a powerful magnet. If you're using a magnet that actually has a 500 lb lifting capability, and you happen to latch onto something that weighs several hundred pounds, how are you going to lift it ?
Ted

 

[D.sebens]

What I know about magnets wouldn't fill a teaspoon, but I'm curious about why you want to use such a powerful magnet. If you're using a magnet that actually has a 500 lb lifting capability, and you happen to latch onto something that weighs several hundred pounds, how are you going to lift it ?
Ted

The issue is that rating would be for a perfectly centered load with flat contact. Using a shopping cart as an example, if you latched on to that it probably weighs 30lbs and is stuck in the mud for a total pull of 60lbs. A 500lb magnet probably won’t do it due to the very little contact a round leg or handle has on the magnet face. That’s why you go for a really high lifting capacity.

Plus it seems that all the Amazon ones are lying based on reviews.

 

[homebrewed]

The lifting power of your magnet also depends on the thickness of the metal -- here's another web page on the subject. So there are a number of factors that conspire to reduce the actual lifting capacity.