Basic Male Form by Nicholas C. Lewis

Nicholas C. Lewis uploaded a model Basic Male Form to Thingiverse just as I was starting a build that had a little unused volume in it. On a whim I downloaded his model and scaled it to fit. It fit neatly into the leftover volume, so I got an extra model without using any additional material.


His original was 10 cm high, but I scaled it down to ~2 cm to fit within my existing build envelope, so I got a very tiny but very detailed model from the SD300.


It looks pretty on my $3 light table from American Science and Surplus. It's amazing how easily I can build an extra model for so little effort.

"Snap" assembling a Nut

I never seem to have the right fasteners on hand for my projects, so I like to design things that can be assembled without screws. This nut-themed shell is designed so two identical halves can snap together, leaving ample room for the mechanism inside.


For testing, I assembled two halves without installing the mechanism. The part was built with a combination of opaque white material and transparent material, which makes it striped.


The round bumps will fall into matching holes when the part is squeezed together. This is a very rigid part with thick walls, but the SD300's PVC material has just enough 'give' to allow these halves to be snapped together securely.


Thanks to the layers of transparent material, the assembled shell includes windows through which the mechanism will be visible in the final puzzle.

Magnet bearings

I've wanted to develop this, even before I owned an 3D printer.

Oskar's 8-Inch Bolt is a cylindrical incarnation of a hysteresis maze, where the user can move a collar up or down but can't turn it from side to side. The collar has a pin that traces from side-to-side along the walls of a maze, but the user can't steer it. There are very few samples of the puzzle in existence.

I liked the premise of Oskar's 8-Inch Bolt, but the collar operated very poorly due to excessive friction. Sometimes I tried to share the puzzle with other puzzle enthusiasts, but it moved so roughly that only one could even make it work. So I've been developing a low-friction replacement collar.


I designed the replacement collar as a disc studded with 24 magnets, which would be sandwiched between two additional rings of magnets. The magnets are all configured in repulsion, so the central disc tends to hoover. This minimizes friction, yet the magnetic repulsion ensures the ring won't rotate unless it receives some lateral force.


In later prototypes I added a channel with nylon ball bearings so vertical forces won't cause the disc to rub against the other parts. (Nylon is unaffected by the powerful magnets.)


The current prototype seems to exhibit exactly the right behavior. The central disc effortlessly rotates in response to sideways pressure on the pin, but it stops at predefined positions and stays put.

More marbles?

Maybe I'm stuck in a rut, but I've built a substantial number of test marbles using various build orientations, color schemes, and tolerances.


Some are twisted in the reverse direction. I plan to use them as building blocks for a larger puzzle by gluing some halves back-to-back so they have to be attached to other parts in a specific way.


Despite all the different tolerances, the pieces are similar enough to mix-and-match. When two halves are joined into a single marble they usually hold together firmly, but some pairings will spontaneously disassemble themselves as captured in this video.