What You Missed: Subtraction Final

Yeah…so towards the end of last semester things got busy. As they do. And I neglected my blog for a bit. Now my summer trysts are over and I’m back at it. Starting with a series I’m calling What You Missed. This is (possibly) the first in a series of posts catching up on things/events that have transpired and deserve a blog post but don’t have one yet.

I’m starting with my final project from Ben Light’s Subtraction.

The Cryptex

So here’s the thing about the Cryptex…it’s sort of a made-up real object. Cylindrical coded objects safes have been around for a while. The Jefferson Disk is proof. But the neologism “cryptex” was coined by everyone’s favorite author of mysteries kicked into motion by shadowy ancient organizations, unbreakable codes, and the fate of the free world/religion: Dan Brown. A physical version was build for him and subsequently patented in 2004. Just for the hell of it I guess.

For my subtraction final I decided to make one using just the metal lathe. (The 4-axis mill came in handy too as an overpowered drill press as you’ll see later.)


A cryptex™ has 3 main components. An inner sleeve with pegs. An outer sleeve with a channel. And x-number of rings that form the locking mechanism, depending on how long your cryptex is. They go on the outer sleeve. Then The inner sleeve fits into the ring/outer sleeve assembly. Simple enough.

Except that the rings need to fit all these little pegs on the inner sleeve and they need to be able to rotate until the holes line up and the interior sleeve can slide out and there can’t be any gaps on the exterior. (Think bicycle lock.) So the rings are designed with a recess on the interior for the inner sleeve’s pegs to sit in and still allow the rings to rotate. If it isn’t clear yet, keep going. All will be illuminated.

(Was that an Illuminati reference? Is Cole part of the Illuminati? These are all good questions to be asking.)


I started with two stock materials. One was a length of .75″ aluminum rod for the inner sleeve. The other was a length of 1.25″ aluminum tube for the outer sleeve and rings. At this point all of my measurements were done so it was a matter of machining the parts to spec.

Milling the Sleeves

Milling the Rings

After I checked my tolerances, I started milling the rings. Each one needed to nest into the next, while leaving enough room for the pegs to sit inbetween each ring.

4-axis for 2-axis

I needed a few precise operations done that I a) couldn’t do on an unmodified drill press b) couldn’t rig up a modification on the drill press that was safe/satisfactory c) would have taken forever if I had trusted the 4-axis on it’s own. So I opted to take the literal wheel and control the 4-axis by hand. Essentially using it as a 2-axis, hand-cranked mill.

For each operation I set the spindle speed and, very carefully, moved the bit little by little.


Power Coating

Power coating uses the principles of static electricity to evenly and completely coat a metal object in a plastic-y paint-y type material. Then you bake it. The material melts together, sets, cools, and you’ve got a powered coated thing. As much as I liked the metal look of the raw aluminum I thought this would lend an air of “finishedness” to the project. It sort of did. The coat was even-ish on the sleeves. But I coated the rings twice which gave them a slightly different color.


The arrows and dots helped me keep track of the interior slots and where the pegs/channel were so that I could easily slide the assembly apart and back together.

Photo May 06, 10 46 27 PM

The finished* cryptex.



*After several failed experiments with electroplating and laser cutting, I still never arrived at a satisfactory solution for a code around each ring, so I just put on some stickers. Which, I know, defeats the whole point of it locking to being with.