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Hollow Coins? Answered

Does anyone know how to go about hollowing out a coin to conceal a MicroSD card or USB storage device? Like this one: http://makersmarket.com/products/micronickel-hollow-spy-coin What is the bare minimum toolset that I would need?



Best Answer 8 years ago

I'd guess that they've taken two coins and turned a face off of each on a lathe, then turned hollows.


Great answer. I'd never thought of it that way.

However these are machined, they look like real coins. The tricky-part will be mounting the things. I'd like to know how they do that, but I have ideas...


You machine two coins, one hollowed out and the other one has the edge removed (and thickness reduced) to a squeeze fit. A collet can be made to hold the 'cup' coin, and, if done carefully, the 'face' is glued (epoxy or other solvent or heat-release glue) onto a faceplate. The hole is slightly smaller than the face with a stepped edge so that the face doesn't fall too far in.

#That's sound. (Some of us are thinking of trying)


Two places to look for inspiration: A book called 'Numismatic forgery" and magic coin trick design.

On this occasion we were thinking instead of researching (for fun). Thanks for the tip though.


They may silver solder them. That would create a seamless joint on "silver" coins.

Solder sounds a bit permanent - the stick-together / come apart-bit I don't get.


The only one I had ever seen folded in half.

Now I looked at some on the internet that looked like they were chucked into a lathe and a lathe tool used to mill out the recess on the coins.

The closure is a milled snap like the old time plastic medicine bottles.  the ones before childproofing.

Ah right, Steve and I were thinking of a lathe-turning, might even try it.


Looks like I need to start lookin for a metal lathe.

If you want to go poor man DIY, you can take a penny (made after 82) and a file and some muratic acid from a home improvement store. nick the copper with the file untill you get to the zinc core. then submerge the penny into the muratic acid for a bit untill it eats the insides out of the penny. You will end up with two sides of penny stamped copper "foil" that can be used to secure the micro sd card.

Lemonie has the process exactly right. As for tools, you can't do this with hand tools and I wouldn't try it with anything but a metal lathe. But it would be pretty simple and straight forward with one.

You could possibly use a three-axis CNC, but it will be hard to secure the coins in a way that doesn't interfere with the mechanism. (At least in the ones that I'm familiar with.)

Is there enough material left in the rims to create a thread?

Could you not grind it out with a dremel?

If you had to mill it, the simplest way is just to epoxy the coin to something that fits in the vice of the machine, then boil the coin in a pressure cooker for 10 minutes to destroy the epoxy afterwards.


In the sample, you can see the tooling marks from the lathe.