Orange, Green, and Blue Marble

George Bell graciously took several sets of my Bag of Marbles puzzles to the International Puzzle Party in Berlin this year. Currently I have three styles of marbles, distinguished by color.



Orange Marble was my first design, a puzzle with two interlocking pieces that slide together unintuitively. It was created by accident as part of a design that I abandoned while studying Bram Cohen's Trapped Marble prototype. Although the two pieces are different from each other, they can be flipped relative to each other and they slide together symmetrically.


Green Marble is another two-piece design. This time the two pieces are identical, but they only fit together when the pieces are oriented in one specific orientation.


Blue Marble is based upon the same curves as Green Marble but divides a sphere into three pieces instead of merely two. Most people fit two of the pieces together easily, but instinctively try to insert the third piece upside-down...which doesn't work.


Here's how a batch of Blue Marble pieces looked shortly after I'd removed them from the SD300 and removed some of the support material.


Unprocessed pieces have a translucent sidewall finish. It's attractive, but I wanted a shinier smoother finish.


To smooth the side walls I dipped each piece in Weld-On 2007 solvent for 30 seconds.


After their solvent bath I laid the pieces on baker's parchment to dry. Parchment is non-absorbent and the wet pieces don't stick to it, so it's an ideal disposable drying surface.


Eventually I plan to add other Marble styles (and colors) to the series as I think of new challenging features to add.

Wrong Way Nut

A moderator on my favorite puzzle-building forum called attention to a YouTube video entitled Magic Nuts and Screw Threads in which two nuts are shown unscrewing in opposite directions on the same threaded rod.

I don't have any inside information about the trick nut in the video, but I conjectured I could build a nut that would behave like that. The threas on my first test model turn a bit tightly, but it works!

I will record a better demo video later. It could use a little refinement, and the screw threads need to be a lot longer for a better demonstration. But it's sure gratifying when a new idea passes the proof-of-concept test on the first try!

My first functional Yoshimoto Cube

Ultimately I would like to 3D print a fully-functional Yoshimoto Cube in one piece, but I really need a solid reference model to help me visualize the design. So I used the SD300 to build the individual hinged panels and glued them together one-by-one.

This black one is almost assembled; the hinged panels at right will be joined with the already-assembled group at left.

I built and assembled a pair of Yoshimoto cubes, one in black and the other using transparent amber.

The geometry of a Yoshimoto Cube is peculiar and confusing, so it'll sure help to have a physical model for reference! So far I've observed a few details that could enable me to build the model in one piece.

Yoshimoto experimentation

In July 2010 I saw plans on Thingiverse for building a kit that could be assembled into a Yoshomoto Cube, which is a type of folding puzzle. At that time I didn't have much experience with hinged models, so tried to adapt the concept.

I built a pair of experimental models that had hinges in each axis, some horizontal some vertical. This picture shows the two models before I'd finished removing all the support matieral; they look like they're attached, but I subsequently separated them.


One separated, the models could fold along the hinged connections. They were somewhat delicate (and tiny!) but each could be folded into many shapes just like a Yoshimoto cube.


Careful folding and unfolding would permit the model to change shape until it was inside-out from its starting position. The model on the left has been inverted, while the one on the right has been returned to its starting position.


Also like a Yoshimoto cube, the inverted and non-inverted models could be nested together in such a way that the combined pair could still be folded in all the same ways as before.


After a few hours' of use both models broke along one of their vertically-oriented hinges. I didn't continue with the project at that time...and now a year has passed by.

Recently I've gained a lot of experience building models with built-in living hinges, so I want to try experimenting with the Yoshimoto cube again soon.

Flexible Burr...Cuburr?

Here's a picture of the current revision of my flexible burr puzzle. I've adopted a scheme with a distinct color for each type of part.


Assembling the parts depends heavily on the flexibility of the material, as the parts must be distorted to fit through each other.


It looks like a mess, but the puzzle is almost solved.


The last step is to fold the faces flat and hook the corners together so it holds a cube shape.


I carved the puzzle's name "Cuburr" into one of the faces in the 3D data, which caused the SD300 to trace it like line art.


That last trick exploits a limitation of the SD300's build process: in the STL data the letters were rendered as cutouts in flat wall, narrower than 1 mm. The SD300's XY plotter can cut with 0.1mm precision, but regions narrower than 1 mm are left bonded to the layer beneath; you have to pry them mechanically if you want them removed. For situations like this, it's a convenient way to emboss line art onto a flat surface.

A flexible burr puzzle

(7 Feb 2013) I notice some debate about this post elsewhere online -- if you have questions feel free to leave a comment or contact me via the email address in my profile (right).

 
In 2002 George Miller devised an unusual puzzle titled Three Card Burr, made by laser cutting slots into three ordinary playing cards so they could be interlaced together. Interestingly, there's no practical way to disassemble the cards after the puzzle has been solved.


I was inspired by George Miller's Three Card Burr puzzle to create a more complex puzzle to exploit the SD300's ability to build sheet-like structures by creating a 3D model whose geometry can be mapped to the build material. I designed this flat model whose middle section is nominally 0.51mm thick, so it will be built using three thicknesses of 172-micron PVC sheet. The adjacent areas have two 0.34mm thick panels stacked one above the other and attached to the middle section by a 0.17mm thick strip to act as a hinge. The whole model is about 120mm x 70mm x 0.9 mm.


Here are my first 3 sample models, built in transparent material.


Like Three Card Burr assembling the puzzle begins by carefully interlacing the sheets together. It wasn't as difficult as I'd expected because the resiliency of the PVC material enabled me to flex the puzzle without tearing it.


Once the pieces are interlaced together, the hinged panels fold out and interlock at the corners to form a cube. This part was far more difficult than I'd expected because each corner depends upon its neighbors for stability, which meant each corner would come apart when I tried to assemble the next corner. I'd forgotten to allow for the thickness of the material in the corner dimensions, so the panels warped from excess tension.


Not bad for a first try, though. It proves the concept is basically sound; now I just have to adjust the dimensions and add something to make the corners more stable. Maybe a small tab or hook?

Eurofighter

Solido provided a sample model that demonstrates an interesting way to exploit the flexible PVC material. The model prints out as a number of flat, semi-rigid parts with living hinges and flexible tabs.


Fold the parts at the hinges and pass the tabs through openings in another piece.


These tabs tuck securely into the underside of the wing piece, thereby snapping the pieces together.


When all the pieces are assembled in this way, you get a modernized plastic version of the good old 'paper airplanes' we used to make from paper.


This gives me some fresh ideas for foldable models!

Assorted "stuff"

I'm continually building models and often forget to share them, so here are pictures of some recent projects.

I built a three-piece puzzle in transparent plastic. While it was building I used a permanent marker to add three splashes of color between layers, using the technique from an earlier post.


Once assembled the transparent material catches the light and the colors seem luminous!


I built this simple-but-elegant Mini Stand for iPhone & iPod Touch. While it was building I switched between black and white material to incorporate a subtle, decorative stripe. It's a small model so I built 3 of them side-by-side using no more material than just building 1.


A Thingiverse user created a script for Duplicating House Keys using the free OpenSCAD tool to create the model data. But it only makes keys for old Kwikset KW1 lock cylinders, so I think it'd be interesting to update the script for the newer KW10 models.


This Recursive Reuleaux Triangle is the first model I built that was pre-assembled. The parts were built already-interlocked in grooves so the triangles can slide around freely but they can't come apart.


Pixobox Studio provided the data for this detailed figure of a Human Head. I had reduced its size to 28% to fit it within volume left over for another model I was building. The Z-axis layering is plainly visible at this low resolution, but it has excellent XY surface detail. There's some tiny text on the sidewall, just below the chin.


Here's a view of the back of the statue, showing the surface details in the hair and more tiny text carved into the back wall of the figure.


Last month I ran into a challenge trying to disassemble part of my car. This spring needed to be tightly compressed to open another access panel, but it's offset from the opening where it's awkward to reach with ordinary tools. So I simply built my own tool with the SD300.


So I 3D printed this simple plastic tool, which has two built-in elbows that reach around and compress the spring. The tool has 1cm thick walls, so it was extremely strong...which was lucky because I had to be surprisingly forceful to release the spring completely!

Building hollow parts "as solid"

Unlike most other 3D printers, the SD300 builds solid parts faster than hollow ones of the same size. Hollow parts require just as much material as solid ones, so I generally make my designs as thick and solid as I like.

But I know many designers who optimize their designs for Shapeways White Strong & Flexible material, so they typically design hollow parts with very thin walls to minimize costs. The SD300 isn't very suitable for very thin freestanding walls, but could I build such models if I just left the support material embedded inside? Would it sacrifice functionality or strength?

A colleague graciously lent me a set of STLs that had been optimized for the EOS with exterior walls only 0.8mm thick and I set out to build them with peeling cuts arranged to leave the support material trapped inside.


I built a small batch of test parts without any trouble. Because the support material is trapped inside they feel like ordinary solid parts, but they aren't quite as transparent as solid parts usually are. The interiors are somewhat cloudy, undoubtedly because the SD300 cut and masked the material inside to facilitate removal. They looked perfectly acceptable, although I have my doubts about their durability.


It went well enough that I tried another batch, then another. A big piece broke off while I was peeling the last batch of parts. The chip (at top right) is still attached to the support material, and the pin is pointing to the surface where the chip broke off. If you look carefully you can see the thin, triangular border which was the only region that had held it together. Not surprising, really.


I repaired the break by putting the piece back and running welding solvent (Weld-On 2007) over the model. The solvent helped glue together the surface of the model, but the support material remained safely un-bonded so it could still be peeled away. Apparently the SD300's Anti-Glue coating works against Weld-On.


I test-assembled some of the parts; they didn't fit together as accurately as parts built from solid STL data. That makes sense in hindsight. Using "hollow" STL data meant the interior material wasn't continuous because the SD300 had made cuts for the interior walls and had masked the interior layers with Anti-Glue.


So the experiment answered my basic question, could I build STLs that had been optimized for EOS or other thin-wall technologies? Yes, I could build test models with restrictions on their usefulness:

• The support material would have to be left inside, so hollow STLs built as-solid would be much heavier than a hollow model built on an EOS.
• Such models would not be as strong as solid models, despite their solid appearance, because the interior isn't bonded together like solid models.
• Such models aren't as dimensionally accurate as models build from solid STL data.
• Such models aren't as transparent, even when built with transparent material.

If I intend to build parts on the SD300 I would not design them with thin walls like these, but the technique is potentially useful for verifying the basic size, shape, and dimensions of STL data that's optimized for another build process.

Efficient peeling cuts revisited

Here's another example of how to arrange peeling cuts for efficient cleaning of an SD300 model. The user adds peeling cuts (the purple walls) while preparing to build models in the SDView software. Peeling cuts don't affect the model, but they instruct the SD300 to cut the support material that surrounds the model so it can be torn away conveniently.

When I had just learned to use the SD300 I tended to put peeling cuts between each individual model to isolate them, resulting in lots of small areas that had to be cleaned one-by-one. But I eventually learned to arrange models so the peeling cuts could be joined and streamlined, peeling several models at once.


These nine models have two continuous peeling cuts that follow the geometry, so the two exterior regions can be peeled away in an easy continuous motion.


After the two outer strips have been removed the models are still connected by leftover support material between them. Much of this can be peeled away in the same manner, as the top and bottom areas are continuous just like the other strips were.


There's still some support material embedded in the middle layers between models, but it doesn't have to be removed layer-by-layer like the other strips. Instead I just loosened up the support material by squeezing a probe between layers in several places...


...then I gripped two adjacent models and gently twisted them to-and-fro, which gradually loosened the support material between the two adjacent pieces. In about 10 to 15 seconds the leftover material was loose enough to free the two adjacent pieces, and I moved on to the next pair of embedded models.


All told, it took less than ten minutes to completely clean these models. The same batch of models probably would've taken a half hour or more if I had isolated them with individual peeling cuts. Back when I was just learning to peel and clean models it probably would've taken over an hour, so experience helps too!