Magnetic Money Clip

So you want to make a magnetic money clip...

What is a magnetic money clip?

Two attracting magnets provide the clamping force in a magnetic money clip.

A traditional, old-school money clip is usually made from a length of spring steel fashioned into a clip.  It doesn’t get much simpler than that.

What if you want to use a pair of magnets instead?  How well does that work?  How do I make one?  What challenges should I be aware of?

Magnets don’t act the same as springs.

The more you pry open a traditional money clip, the greater the force. In a magnetic money clip, the force drops as you shove more money into it.

There is an important difference in the way a mechanical clip acts, compared to a magentic one.  This may sound like obvious common sense, but a mechanical spring clamps down harder as you open it more.  The more dollars you stuff in the clip, the greater the clamping force.

With a pair of magnets, the forces are just the opposite.  The force is strong when the magnets are close together, but get weaker as you move the magnets further apart.  Unlike a mechanical spring clip, our magnetic money clip will get too weak if we stuff too many bills in.

Should I worry about credit cards?

High coercivity cards are usually black or silver. Low coercivity cards are brown.

Yes.  Magnetic fields can scramble the data on a credit card’s magnetic stripe.  While many payment processors are using the more magnet-proof chip, the old magnetic stripe is still used.  It's nice if your wallet doesn't erase your cards!

We talked about this phenomenon in way too much detail in our earlier article, Credit Cards and Magnetic Stripes.  Key points include:

There are two types of credit cards: The low-coercivity cards used for hotel keys, subway tickets, etc., and the more durable, high-coercivity cards used for bank and credit cards that get more long-term use.  It’s easier to erase a low-co card (~300 gauss) than a hi-co card (~4,000 gauss).

With either card type, use distance or shielding to avoid scrambling the stripe.  Keep the magnets a safe distance away from the stripe, add a layer of steel between the magnet and the card, or both!

Do not put credit cards between the two magnets!  The field is very strong there.

The proof is in the testing

Naturally, we had to get our hands on some magnetic money clips to test.  We measured the field strength in a few of them, and then tested them with high and low coercivity cards.

We found that some of those off-the-shelf clips and wallets are probably OK with durable, high coercivity cards, but can erase the low coercivity cards like hotel keys or subway passes.  Adding a layer of steel blocked the fields nicely, but does add weight to the wallet.

What magnets should I use?

In between your two magnets, you’ll have at least two layers of material (leather?) and some amount of cash.  The force you feel between the two magnets depends on the distance.

In the rough prototype we made in the video, two 1” x 1/2” x 1/16” thick BX081 magnets felt nice.  That’s a thinner magnet than what we found in the money clips we took apart.  Of course, the card stock we used is much thinner than their leather.

When we added two layers of steel on the outside of the magnets, we felt even more strength.  This has several advantages: you get more strength from the magnets, you potentially avoid issues with credit cards by shielding some of the magnetic field from reaching outward, and it sticks much less to steel surfaces on the outside of the wallet or money clip.

With thicker material, you might want thicker magnets.  To simulate this, we added a 0.050” stack of PostIt notes on top of the 0.010” thick card stock – that’s about like 1/16” thick leather.  It held well, though not quite as strong.

Consider trying a few different magnet options for your project.  Experimentation is key to getting the right feel.  Good choices include:

How about one magnet?

Can I use a magnet on one side and a piece of steel on the other?  Though the steel is nice for shielding, we find that the pull force across a gap isn’t nearly as good with a magnet-to-steel setup.  You’d need a much larger magnet to get the same strength, which cancels out any advantages you hope to see with a one magnet solution.  Also, a magnet-to-steel setup doesn't center nicely like two magnets do.

A two-magnet solution seems to be the way to go.  All of the examples we've seen use two magnets.  Learn more about whether two magnets or a magnet and a piece of steel is right for you in our previous article, Magnets vs. Steel.

RFID shielding?

If you’ve been wallet shopping lately, you’ll find some that offer RFID shielding.  These wallets are supposed to block the radio signal from an RFID enabled card from getting out of your wallet.

While this is all very interesting, it’s not really related to magnets or magnetic clasps.  Magnets shouldn't have any effect on radio transmissions or RFID.

Thanks for reading!  If you make interesting money clips with neodymium magnets, please share a picture or two with us!