A Solution to Loose Change

I hate having change jingling around in my pocket. Unfortunately, I always buy everything with cash, and I have an equal dislike for not having change when I need it. I've found it is not enough to have change in my backpack or car, since I can never remember to grab it when I need it. I needs to be on my person.

When I first started having this problem I came up with the idea for a credit card-sized holder that would slip into my wallet and hold 100 cents in assorted coinage. I was only able to realize this concept recently when we bought a 3D printer, but I am very happy with the results.

The concept was that the card would have holes cut into it at the right diameter to hold each coin snug in place. The intention was for one side to be solid to prevent the coins from falling through. In the final model each coin hole has a smaller hole going all the way through to make it easy to pop them out.

I started by measuring each coin with calipers and then modeling a test ring with a diameter slightly bigger than the coin. I created all the test rings in 123D Design and printed them with the setting I intended to use on the final print. Once the ring was done I would test fit the coin, and make adjustments to the model as necessary.

I didn't experiment with the sizes as much as I could have. I was also convinced that I wanted sizes loose enough for the coins to fall out if I dumped it into my hands. Both these decisions led to more tests and versions of the project, but that's what making is all about. In the final model I ended up making each hole a fraction too small and then scraping the inside with chisel until it fit the coin perfectly.

The final diameters that I printed were Quarter: 24.6 mm Nickel: 21.7 mm Dime: 18.3 mm

The final card is 2.4 mm thick (about the size of three credit cards) and the bottom support layer is .6 mm

I started the model with a rectangle the size of a credit card. I decided to use 3 quarters, 2 dimes, and a nickel. This gives me change for anything to the nearest five cents. I then added circles at the diameters that I had decided for each coin. I moved the circles around by dragging the center points until they were all equally spaced and not too close to the edges. Then I drew smaller circles inside all the larger circles; these would be the holes used to pop the coins out through.

I extruded the main portion 2.4 mm and all the inner support sections 0.6 mm. I was printing the card with layers 0.2 mm thick. I decided that three solid layers on the bottom was good, and the top portion was 1.8 mm of material, which would hold all the coins flush except the nickel, which protrudes 0.1 mm. These measurements also kept everything in 0.2 mm increments.

After extrusion I filleted the edges with a radius of 4.5 mm, because it looked right, and exported into STL.

After creating g-code in Cura, and converting it to the format that the printer takes, we started the print in PLA. It went fairly smoothly, though the first layer had trouble sticking to the bed. We turned off the heated bed and just laid down glue stick, and that seemed to work well with most of the prints. The model took roughly 40 minutes to print and 2.5 meters of filament.

I printed the first version and was unsatisfied with the hole sizes, so I went back and changed them. In the final version, as I mentioned, I made the holes a fraction too small and used a small chisel to clean it up and fine-tune the fit. I have since printed one more, and only one out of the three has had a little trouble with warping on the bed.

The final model and g-code of the coin card are included below.

This project is finished! I am very pleased with the results. The coins stay in the card even when turned upside-down and don't jingle around at all when they're in your pocket. And when you want them, you can pop them out easily with one hand. The card is about as thick as 3 credit-cards, but that being said it does not seem to take up a bunch of space in the wallet. In my opinion it is much more convenient, space-conservative, and easy-to-use than any other method of carrying change.

I am very happy with my coin card and I already have several people who want their own. Please let me know if you have any questions about the project or the process.