The Care and Feeding of Neodymium Magnets

I have always been interested in magnets. Prior to getting involved with Neodymium Magnets I had about 4 dozen ceramic magnets at various places in my apartment. In the kitchen I have several attached to the side of a couple of cabinets. These provide easy access to various knifes and a pair of scissors. on the front of my office desk is a line of twenty 7/8" by 1 7/8" by 3/8" thick ceramic magnets that hold numerous items. currently I see a pair of tweezers, 2 mechanical pencils, a tiny Swiss Army knife, a small pair of scissors, some small Neodymium Magnets, a small pair of jewelers pliers a drill bit, paper clips and some screws nuts and bolts.   

I got started with Neodymium Magnets when I purchased a $20 Magnetix sculpture kit. After the novelty of kit wore off I used a pair of pliers to crush then trash the plastic parts, saving the pair of tiny Neodymium Magnets. Then I started making some geometric sculptures using only the magnets and steel balls. I had enough parts to construct a 5 level tetrahedron. 

Unlike most sculpture kits which use magnet tubes to hold things together, mine used straight rods which are more difficult to work with. The result though was well worth the struggle. The sculpture is amazingly rigid. I was hooked on Neodymium Magnets and started ordering some on the Internet. 

Now I walk around wearing a Neodymium Magnet bracelet and necklace. This is my "Magnetic Bling". I always carry a few extras which I tend to give away to people that seem really interested in NIBs. Usually I hand out a pair of 1/2" cubes after I demonstrate the power by placing 1 on each side of the person's hand. I show them how to use the edge of a table to separate them and finally I warn them that they are brittle and that they "Bite". Most of the time the next time I see them they will either show me a blood blister or tell me they smashed one. I give them a replacement.

Neodymium Magnets are available in different grades. The most common today are N42 but you can find some as strong as N52. You must determine if it's worth the extra money to buy the stronger grades. Visually, an N52 looks identical to an N42 so you have to trust the dealer to be honest with you. How strong are they?

The magnet is 1/16" dia 1/32" thick N50 Neodymium that weighs 0.000416 oz. and has a pull force of 0.20 pounds. The solid non-magnetic steel ball weighs 2.25 oz. or 5,400 times the weight of the magnet.

Neodymium Magnets are both strong and brittle. If 2 of them are allowed to fly together, one of them is bound to chip, break or smash. When experimenting this is inevitable. When buying magnets be sure to order a few extra so your experiment won't be 1 magnet short of what you need.

Eye Protection is necessary when you play with NIBs. Neodymium Magnets are very brittle. When they snap together they will frequently chip, break or shatter. When they do sharp pieces may fly around at a very fast speed. Personally, I like a full face shield. When ordering Neodymium Magnets for an experiment get a few extras to compensate for the ones that will break. Thick magnets tend to chip while thin ones break or shatter. Thin disk magnets with center holes are especially delicate.

Storing Neodymium Magnets in an organized manner is a point of concern. If you only have a few of them you can stick them together and attach them to something but when you have hundreds...

For my small magnets I use a small parts case with separate compartments. Those are steel balls in the plastic bags at the bottom. My large magnets are kept on the side of my refrigerator, nicely spaced. One of them holds a small telephone book to a door. 

Naked Neodymium Magnets are subject to oxidation. The Iron in the mixture rusts easily. That is why most NIBs are triple plated with a layer of nickel then copper then nickel again. Some have an additional plating of 24 karat gold. Spherical magnets easily wear through this plating at the points where the poles are located.

Frequently you will see Neodymium Magnet advertisements saying that a magnet's strength is something like 13,200 gauss. This is the Br_max (Residual Induction) - Also called "Residual Flux Density". For the hobbyist, this value is essentially worthless. All N42 magnets have a  Br_max of 13,200 Gauss. It doesn't matter weather it is a 1/16" dia by 1/32" disk with a pull force of 0.2 lbs or a 2" cube with a pull force of 348 lbs, all N42 magnets have a  Br_max of 13,200 Gauss. N35 magnets have a  Br_max of 12,100 Gauss and N52 of 14,800 Gauss.

The gauss, abbreviated as G, is the cgs unit of magnetic flux density in a magnetic field (B), named after the German mathematician and physicist Carl Friedrich Gauss (1777 - 1855). One gauss is defined as one maxwell per square centimetre. http://en.wikipedia.org/wiki/Gauss_%28unit%29

Another rating method you may run into is the Surface Field Strength. This is a direct reading with a Gauss Meter at the surface of a magnet. As an example I have listed the Surface Field Strength and the actually measured Pull Force of a series of 1" N42 disks/cylinders. 

1" dia. x 1/32" thick = 1275 Gauss, 45.67 lbs
1" dia. x 1/16" thick = 1795 Gauss, 55.75 lbs
1" dia. x 3/32" thick = 2310 Gauss, 59.14 lbs
1" dia. x 1/8" thick = 2820 Gauss, 62.53 lbs
1" dia. x 1/4" thick = 4520 Gauss, 65.60 lbs
1" dia. x 1/2" thick = 5835 Gauss, 69.00 lbs
1" dia. x 3/4" thick = 6250 Gauss, 70.40 lbs
1" dia. x 1" thick = 6690 Gauss, 74.20 lbs
1" dia. x 2" thick = 6775 Gauss 75.17 lbs

For Graphs and More Info on This Click Here

Pull Force is the actual lifting power of any given magnet under ideal laboratory conditions. The Magnets is attached to soft steel plates at least 1" thick. the force applied is perfectly perpendicular to the steer plates. The plates have smooth surfaces. Factors that effects the actual Pull Force includes chemistry of the steel, thickness of the steel, the smoothness of the surface, surface covers like paint and the direction of forces applied. All of these factors lessen the actual pull force of any given magnet on any given surface. Still Pull Force is the best indication of the magnets strength. 

I store my large NIBs on the side of my refrigerator. The steel on the outside walls of it is probably 22 gauge or 0.031" thin. Because this is so thin I can place and remove my 2" by 2" by 1" blocks, with a rated pull force of 325 lbs, quite easily (although it takes 2 hands). When I place them on 1/4" or thicker plate steel I have no chance of picking them up without one of my special tools. When I place this magnet on my 1.05" thick Iron plate it feels like it is welded to it.

My Studio/Shop Refrigerator Loaded With Hundreds of Magnets.

I remember an episode of MythBusters where Jamie used several 3" dia by 1" thick Neodymium Disk Magnets to successfully climb up some vertical ductwork. It is because of the thinness of duct walls that he was able to succeed. If the ductwork was made from plate steel then Jamie would never have been able to have moved them with his climbing devise.

Pull Force Calculators can be found on the Internet but I find them extremely inaccurate and therefore totally worthless. Here are a calculator's results for a few 1" N42 disks/cylinders.

1" dia. x 1/32" thick, 0.27 lbs  (Correct PF = 45.67 lbs)
1" dia. x 1/2" thick, 44.77 lbs  (Correct PF = 69.00 lbs)
1" dia. x 1" thick, 89.54 lbs  (Correct PF = 74.20 lbs)
1" dia. x 2" thick, 179.08 lbs  (Correct PF = 75.17 lbs)

As you can see, the values listed are nowhere near the actual laboratory measurements in the previous table. The pull force calculators appear to assume that if you double the thickness you get double the pull force. This is WRONG.

Stacking Magnets

Neodymium Magnets come in hundreds of sized but you can save money by stacking. A 1" dia. x 1/8" thick has 2820 Surface Gauss and 62.53 lbs Pull Force. If you stacked 8 of them together you would have the equivalent of a 1" dia. x 1" thick with close to 6690 Surface Gauss and 74.20 lbs Pull Force. In this case 8 thin magnets typically cost less than 1 thick one. Best of all, you have lot more versatility with the 8 as opposed to 1. Another advantage is the fact that you can separate the thin disks easily by sliding them apart. A couple of thick ones, with their higher surface gauss, is many times harder to separate. The disadvantage is that thin ones break a lot easier than a thick one. 

On the right is a 1" by 1" by 2" thick NIB magnetized through the 2" thickness. On the left are four 1" by 1" by 1/2" thick NIBs all magnetized through the half inch thickness. In the middle are two 1" cubes. All are N42 and for virtually all practical purposes the three are identical. The stacks equals the block and vice versa. Typically the four 1/2" thick magnets would cost less then the pair of cubes and the single large NIB. A point you must consider though is the fact that the thinner magnets are more likely to break in 2 while the larger ones would be subject to minor chipping. 

Spheres

Neodymium Magnet Spheres are something different. They are representative of the Earth with its North and South Poles. They rarely chip and break, though the plating at the point of the poles will wear through exposing the NIB material. When they snap together they are more merciful on fingers. Rather than pinch they tend to push fingers aside as they slam together. I've never had a sphere chip or break on me.

Small spheres make for fun Jewelry. I walk around with a string of eighty ¼” around my neck. I have a girlfriend who is hemiplegic from a massive stroke (her left side is paralyzed). She absolutely loves the Neodymium Magnet Jewelry I’ve given her, especially her matching necklace and bracelet of gold plated ¼” spheres. Imagine trying to put a bracelet on your right wrist using your right hand. One problem with spheres is that they are too strong for their Nickel-Copper-Nickel plating. 

All the magnetic forces are concentrated at the 2 points at the poles. This is most notable when spheres are used for jewelry. The only way to prevent this is to make sure they never contact another NIB or hard steel.

NIBs Are Very Brittle

Soon after you begin playing with Neodymium Magnets you will start collecting broken or chipped magnets. Thin ones break very easily but even the big ones, like this 2" dia. by 1" thick monster, are subject to destruction.

Protect Your Neos

Neodymium Magnets are very brittle. This demo shows a couple of ways I keep NIBs from smashing when they strike another Neo.

This is an example of Diamagnetic Levitation using only 1 piece of polished Bismuth. I polished the Bismuth to creat the illusion that the floating height is twice what it is. It is inevitable that the cube will fly up and smash into the 2" dia by 1" disk. To save the cube from destruction I illustrate 2 methods that I use to cushion the blow. On the top I glued a 2 1/8" dia by 1/4" soft wood disk to the Neo. On the bottom I have several coats of clear dipping plastic. Both are soft enough to absorb enough energy from the floating cube to keep it intact when it inevitably smashes into the monster. 

North or South?

All of these permanent magnets have a north and a south pole. Some Neodymium Magnets, specifically computer hard drive magnets, have a north and south pole on each side for a total of 4 poles. Damned if I can figure how they do that. Some advertising for "therapeutic" magnets, referred to as "BioMagnets", claims to be mono-poled but there is no such thing as a single poled magnet. If you have a north pole you must also have a south pole. There is absolutely no difference between a gold plated Neodymium Magnet and a BioMagnet except for the outrageous price they charge for BioMagnets. One company, Healiohealth2.com, charges $79.95 for twenty 1/2" dia by 1/16" thick N35 magnet. Magnets worth way less than $10. The widely TV advertised Zerosmoke consists of a gold plated 1/4" dia by 1/16" thick disk that you wear on the front of your ear held in place by a 3/8" dia by 1/16" thick disk on the back of your ear. The price, $39.95 for 2 magnets worth less than a buck. Do they work? Can you say "placebo"? I expand on this subject below.

We know that opposite poles attract and like poles repel but how can we tell which pole is which? The most common way is to use a regular direction finding compass. A compass north pole will be attracted to the magnets south pole and vice versa. There are commercial devices available to distinguish between poles. One is a Magnetic Pole Identifier which works on the same principle as the compass. Another device, and my favorite, is the Electronic Pole Identifier.

Since many experiments require the knowledge of which pole is which, you  should at least invest in a compass. The pic on the left shows the compass north arrow pointing to the NIB's south pole. The Magnetic Pole Identifier, in the middle photo, is a cool little device but it is too delicate to use with Neodymium Magnets. If it's magnet comes in contact with a NIB it will disassemble itself when you try to separate them. The Electronic Pole Identifier is neat. It beeps when it identifies a pole as well as shines 1 of 2 LEDs indicating which pole is detected. In this case a green light indicates that it is pointing to the south pole.

"Therapeutic Magnets"

When someone wants to use a Neodymium Magnet for medical purposes it suddenly becomes a "BioMagnet" and cost 10 times more. I see no way that a weak little magnet can have any influence on the human body. Ever since a Greek Shepard named Magnes found a rock that attracted iron supernatural powers have been attributed to Magnets. 4,000-years-ago in China the "Emperor's Book of Internal Medicine" prescribed magnetic stones to correct health imbalances. Cleopatra slept with magnets to keep her beautiful. Homer, Hippocrates, and Aristotle are said to have written about Magnet Therapy. Personally I think it's all a pile of crap. I see no way that a small magnet can have any influence on the human body that could possibly affect bodily health. And the statement that only the "negative" (South Pole) side of a magnet must be applied to skin defies all logic. I especially despise the scam artists who prey on the people in pain by selling overpriced, worthless products that they guarantee will relieve pain and suffering.

On the positive side (of the issue, not the magnet) it does have a placebo effect. This is definitely a case of ignorant bliss. Now the Placebo Effect isn't all that bad. If people think that magnets are having a positively influence on their health and as a result they are feeling better or sleeping better or taking fewer pain pills, then that can't be all bad for that individual.

How Strong is Strong?

I've given away several dozen pairs of 1/2" cubes and rate them as MEDIUM strength. I have seen many strong men struggle and fail to separate them by hand. Anything smaller than that or with a pull force less than 20 pounds I rate as LOW strength. Anything as big as a 1" cube or 100 pound pull force is rated HIGH. Anything with a pull force of 200 pounds or more I rate as SUPER HIGH.

My Strength Ratings by Damage Caused

LOW strength is blood blister territory. 

 MEDIUM strength = cuts and bruises

HIGH strength = broken fingers and bad bruises 

SUPER HIGH = crushed broken hand with permanent bodily damage (including Amputations)

Neodymium Magnets are inherently dangerous. Toddlers have died after they swallowed a couple of tiny ones which pinched off their intestines. One young lad had to have his hand amputated after getting crushed between a couple of 3" dia by 1" thick disks. In my opinion though, I believe the effort of removing the magnets probably caused much more damage than the initial crushing. While dangerous however they shouldn't be feared. Respected, yes but not feared.

Children should be allowed to play and experiment with low strength NIBs. Under adult supervision at first but then let them explore on their own. They will get bitten and suffer pinches, blood blisters or small nicks but they will gain experience and will be less likely to do it again. It's basically like the old joke. "Does it hurt when you do that? Then don't do that." They must, however, be kept away from the ones that can do great bodily harm. Kids love magnets and when they play with magnets they are learning stuff and there is nothing bad about that.