So you want to make 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?
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.
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.
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.
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:
|BX081 Block||1" x 1/2" x 1/16" thick||We used this magnet in the blue folder demo.|
|BX081-N52 Block||1" x 1/2" x 1/16" thick||Same size as the BX081 with a little more strength.|
|BX08H1 Block||1" x 1/2" x 0.1" thick||Even stronger.|
|BX082 Block||1" x 1/2" x 1/8" thick||Perhaps too strong unless material is very thick.|
|BX082-N52 Block||1" x 1/2" x 1/8" thick||Same size as the BX082 but stronger.|
|BX881 Block||1-1/2" x 1/2" x 1/16" thick||A longer length.|
|BX882 Block||1-1/2" x 1/2" x 1/8" thick||Thicker and stronger.|
|DC1 Disc||3/4" diameter x 1/16" thick||A disc magnet alternative.|
|DC1-N52 Disc||3/4" diameter x 1/16" thick||A bit stronger.|
|DC03 Disc||3/4" diameter x 3/32" thick||A bit thicker & stronger.|
|DCH1 Disc||3/4" diameter x 0.1" thick||A bit thicker & stronger.|
|DC2 Disc||3/4" diameter x 1/8" thick||A bit thicker & stronger.|
|DC2-N52 Disc||3/4" diameter x 1/8" thick||Even stronger.|
|DX01 Disc||1" diameter x 1/16" thick||A larger disc magnet.|
|DX01-N52 Disc||1" diameter x 1/16" thick||A bit stronger.|
|DX003 Disc||1" diameter x 3/32" thick||A bit thicker & stronger.|
|DX0H1 Disc||1" diameter x 0.1" thick||A bit thicker & stronger.|
|DX02 Disc||1" diameter x 1/8" thick||A bit thicker & stronger.|
|DX02-N52 Disc||1" diameter x 1/8" thick||Even stronger.|
|SW-M Disc||3/4" diameter x 0.075" thick||A sewing magnet with integrated steel cup, provides some shielding and stronger strength on one side.|
|SW-L Disc||1" diameter x 0.08" thick||A larger sewing 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.
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!
While the K&J Magnetics website has a lot of great information about pull force, there are unanswered questions. What if I have two magnets facing one another across a gap, and I want to know the force to slide them apart sideways?
Let's answer three questions:
Magnetic Hooks Hang Holiday Stuff
This season seems fully of holidays, back to back. Between Halloween, Thanksgiving and Christmas, this time of year always brings us more questions about how to hang stuff with magnets.
Like all of our articles, we’ll test out a few different ideas for the most common questions. We’ll share what works and what doesn’t, hopefully helping folks find the right magnet for the job.
There are rules about how to ship magnets by air, including limits how strength, how to package them etc. We’re going to take a closer look at what this really means when you’re shipping magnets, and some practical advice on how to comply with these rules. We'll measure magnetic fields with super sensitive sensors, a rudimentary compass and a DIY sensor built with an Arduino.
Some of the most popular magnet demonstrations highlight eddy currents. Whether it’s magnets falling through a copper tube or falling against a flat plate, strong magnets move slowly when next to a conductor.
We took a brief look at this in our original Eddy Currents article. It’s about time for a deeper look. We’ll explore a formula that calculates the eddy current forces, and try to merge that theory with experimental testing. We hope to figure out how to estimate these interesting forces.