Documenting the process for a custom 0-99 counter made of relatively nice materials. I am starting with a one off to prove the concept out and ensure everything looks/feels right with the coin. If there’s local demand I’ll design the necessary jigs to batch out multiple at a time and document that process.
Let’s start with a rendering of the coin to keep your attention:
The body of the coin is a single piece that measures ~40mm in diameter by ~3mm in depth.
This is mostly because I already have stock of this size from some fiber laser projects.
You can see in the rendering that there are two concentric rings. These rings are numbered 0-9.
From a user experience, I want those numbers to index in line with the small “indicator” gemstone that sits between the rings. I also want the action to be smooth and relatively easy to manipulate with one hand while the coin is on a table (EG: you shouldn’t have to pick it up to index it)
So we have some questions to answer:
- How do we get these numbers to index
- How are we going to keep these rings in their slots
Both of these issues can be solved by man’s best friend: Magnets
The current plan requires 40 total magnets.
These are 2mmx1mm cylinder magnets embedded into the body and the rings. 20 embedded in the body and ten in each ring with a magnet being embedded under every number. This keeps the rings in the body, allows freedom to slide, indexes appropriately, and will hopefully provide a really satisfying action in the hand 
This raises a few more questions:
- How should we constrain the magnets
- Is a 2mmx1mm magnet the best choice
- Will these magnets be too strong to enable a smooth motion
I don’t have any real intuition about the strength or feel of magnets in this sort of scenario (yet!) so the best way forward would be to stop typing and start cutting! (Or 3d printing…though that’s kind of boring isn’t it)
I have a sneaking suspicion that 3mm magnets may be ~fine and they are much easier to source as they are used in hobby scale modeling and mini figure builds quite a lot. I also suspect that agents in the ring and body may be too strong…I think I’ve got a solution for that if necessary.
That’s all for now, I’ll try to keep updates coming as I move forward with the project.
