Puzzle Overview: Moiré Maze

I've previously posted about the development of Moiré Maze so here's an overview of how it works as a puzzle.  There are a few clues about its solution but no spoilers.

At left is Oskar's Boston Subway puzzle from 2006.  It's a sandwich of acrylic sheets containing laser-cut channels; the bottom layer has 10 parallel channels running north-south and the top layer contains 10 parallel channels running east-west.  It's a criss-cross grid.  There's a layer in between that selectively connects the top and bottom grids at some places, thereby turning it into a puzzling maze.  George Miller constructed the puzzles and put inside a small magnet the user can guide through the maze using a magnetized wand.

It occurred to me to build a similar layered maze using circles instead of straight lines.  Ultimately I developed two layers of concentric ring-shaped channels, one over the other as depicted at left.  The layer at right is sandwiched between the other two layers to selectively allow the user to transfer between the two sets of rings like a maze.

The layers are stacked like this with a mirror on the bottom and a transparent cover on top.  I carefully selected a combination of layer thicknesses and a much thinner magnet to prevent the magnet from becoming turning sideways and becoming wedged between layers, a nuisance Boston Subway sometimes exhibited.

Laser cut acrylic comes with a protective film over the surface.  To avoid getting dust and fingerprints on the layers inside the puzzle, I only removed the protective film after each layer had been assembled into the puzzle.

But there's more to this puzzle than a mere shape variation on Boston Subway--it introduces a visual subterfuge that misdirects the user away from the solution.  The critical secret is plainly visible, even in the photo, but it's tough for a viewer to choose to see it once their mind has resolved the image.  Some testers couldn't even force themselves to see it when the solution was shown to them.

In Boston Subway it was sometimes difficult to locate the little silvery magnet because it reflected the same colors as the neutral mirror and irridescent sheets.  I chose to use a bronze-colored mirror with Moiré Maze to enhance the contrast, so the silver magnet is easier to distinguish against the bronze-tinted background.

As a final touch I gave Moiré Maze a built-in stand that secures the layers and holds the puzzle at a convenient slope for playing.  Initially I'd planned to make the stand with laser-cut acrylic like the rest of the puzzle, but after some experimentation I substituted dark-blue pieces 3D-printed from my SD300 because the PVC material is so resilient that it can squeeze the acrylic sheets tightly together.  If I had made those piece of acrylic, then the stand's outer pieces would be strained in tension and would thus be vulnerable to breakage--acrylic tends to fracture under stress.

A Shower Runs Through it

This is one of those "Gee whiz!" stories about 3D printing...

A coworker recently renovated the guest shower in his home, resulting in damage to a 1970's era plastic drain fitting.  He couldn't find a suitable replacement at any of the hardware stores so I offered to make a replacement.

It took only a minute to model a replacement in CAD.  The fitting just needed a flat grid for water to drain through and a collar (not shown) that extends into the opening in the shower floor.

Here's the replacement fitting next to the broken one.  My replacement part is PVC, the SD300's default material, which is ideal for plumbing.

The replacement fitting is thin but nice and strong because the layers are aligned with the natural laminations of the PVC material.  Since it's going to be used in a wet environment I treated it with PVC pipe primer to seal the edges.

It's not a very exciting model, but it was fun and satisfying because I produced it just a few hours after inspecting the original part.  And I posted it to Thingiverse.

Moiré Maze for laser cutter

I took last month's injection-molded prototype for Moiré Maze and adapted it back for laser cutting by projecting it into 2-dimensional layers and tracing their outlines.  I don't own a laser cutter, but plenty of businesses offer laser cutting services including mail-order Ponoko.  But why wait for the mail?

The SD300 can make good simulations of laser-cut parts, given adequate model data.  I created accurate simulations of laser-cut models by first modeling a sheet about the anticipated thickness of the part, about 3.0 mm to simulate the typical "eighth inch acrylic" (which usually runs a tad thin).  To simulate a laser's cutting behavior I cut the outlines using a "thin wall cut" with a 2 degree draft angle.

Models were easy to clean because the sheet-like design meant there weren't any overhangs, undercuts, or loose ends to deal with.  It was easy to stab leftover support material and peel it away from both sides of each finished piece.

I also designed a 2-piece base, shown upside-down here, on which the maze layers are stacked.  The base aligns the maze pieces and holds them together.

The magnetic wand can be stored in a compartment at the top edge of the maze, and it's held in place because the magnets in the wand are attracted to steel beads embedded inside the model.

Above is a brief video tour of Moiré Maze.

Moiré Maze was inspired by Boston Subway, Oskar van Deventer's design for IPP26 shown at left in the picture.  Boston Subway has layers of criss-crossing channels built from laser-cut acrylic, and the goal was to guide a little magnet from "work" to "home" using a magnetic wand.  Moiré Maze substitutes ring-shaped channels for the straight ones, and thereby creates a visual hiding place for its solution even though it's entirely transparent!

Evaluating Protomold and Moiré Maze

A friend from IPP suggested I investigate a company called Protomold for their expertise in rapid injection molding and wide selection of materials.  Although he was not a puzzle builder himself, he had apparently sponsored production of another designer's puzzle via Protomold and was pleased with their work.

As an exercise I chose to adapt Moiré Maze, a design I briefly tested in 2009.  The original test model contained 5 layers of transparent laser-cut acrylic containing ring-shaped channels.  The goal is use a magnetic wand to guide a small magnet through the channels from start to finish.  The lowest layer is a mirror, which I hoped would create an illusion that would disguise one secret feature so its solution could literally hide in plain sight.

I gave the prototype (pictured above) to several testers, and their toils demonstrated the secret feature was a success.  But the maze as a whole was much too elaborate, the nine pairs of overlapping rings merged into a dizzying kaleidoscope of curves.  The key feature worked, but testers agreed the overall maze was just too complicated.

So I consolidated the inner layers of Moiré Maze into a single 3D model, simplified the maze to just six rings, and added details for a built-in stand that could be injection-molded in a standard 2-part mold.  I requested a quote from Protomold, and in the meantime I built a test prototype on the SD300.

As it turns out, the SD300 is great at building a model that's designed for injection molding because there aren't any overhangs to get in the way while cleaning unused material off the model.  I did need to use a fine probe to clear the smaller channels, but it was easy because I had unobstructed access from both sides.

Both sides of the model needed some sort of lip to hold the cover pieces, so I designed these little tabs.  This tab is an example of a sliding shutoff.  It looks like an overhang but it really isn't--the other half of the mold would project through the hole in order to form the underside of the tab.

It's always good to build a prototype: during inspection I discovered an error in my maze.

Upon correcting the error I built another test model, this time using the SD300's transparent material because the user is supposed to see through the mazes.  My PVC material isn't nearly as transparent as acrylic, and there are blemishes from the SD300's construction process.  But it's an excellent test model!

Also using the SD300, I built a pair of transparent covers.  Above, I installed the back panel into the test model.  The back panel ought to be cut from acrylic mirror material, but a simple transparent panel would suffice for testing.

I dropped a small magnet inside and then installed the top cover.

The challenge is to navigate the maze from start to finish by using a magnetic wand to guide the little magnet through the channels between the two covers.

Protomold replied within 1 business day, giving me an interactive quote that enabled me to gauge the cost of various options.  These folks obviously know their business!  Their versatile quoting system permits the customer to view and evaluate their quote in four distinct ways, at the user's discretion:

• As a straightforward web page (pictured above) with tabs and interactive elements.
• As an enhanced web page with a powerful 3D plug-in.
• As a printable PDF document with all the information comprehensively laid out.
• As an enhanced PDF document that exploits Adobe Reader's ability to view 3D models.

The report called attention to six "required changes" that would need to be addressed for the model to be injection molded.  Five of these were the result of a single error in my model, which caused an undesirable indentation in the walls.  Pictured above, Protoquote's interactive plug-in highlighted the error and explained exactly what action was required and why.

Additionally, the report explained the ramifications of certain attributes that might have cosmetic or functional ramifications on the finished part even though they wouldn't prevent the model from being built as-is.  For instance, the blue marking show where "sink marks" could appear in the finished model because injection molded plastic shrinks as it cools.

After I resolved the "required changes" Protomold supplied an updated report.  Now that the model was completely build-able the report added an informational section calling out foreseeable (but harmless) side effects of the tool-making process.  Pictured above is a sample of the "Printable PDF" version of the report, denoting where sharp corners would come out very slightly rounded as a machining artifact.

It was a valuable experience, and this particular model was probably an ideal choice for learning how to make an injection-molded design.  But, in my final analysis I concluded injection-molding isn't suitable for this particular project in the quantities I needed because:

• This particular design still required laser-cut parts for the mirror and top cover.  Injection molding merely reduced the volume of laser-cut parts per model (from 5 down to 2), it didn't eliminate laser cutting entirely.
• To attain the required transparency the molds would require laborious polishing to a mirror finish.  That polishing would cost more than all other expenses combined, which rendered the project hopelessly uneconomical for a small production run.
• Critical geometry includes a knife-edge "gore" where two arcs converge toward an intersection, a feature not suited for injection molding.  Hence injection molding would diminish the quality of that particular detail.
• The previous test model had already demonstrated the design was suitable for being laser cut.

Still, it would be nice to devise a design that would be optimal (and economical) for injection molding--preferably something I couldn't otherwise fabricate.  Protomold offers a wide selection of engineering materials, including elastomers.  Hmm.  I have an idea that could use Santoprene™...

3d Printer Brings New Light to Antique Japanese Lantern

Ben Sherwood experimented with the use of modern technologies to help repair this 150 year old Japanese lantern.  It was missing a curved wooden rib like the one in the picture, so we 3D printed a replacement on the SD300.

The 3D printed rib fit the size and curvature of the lantern perfectly, thanks to careful measurements that Ben took prior to building it.  But naturally the modern plastic looked a bit funky among all the wood and paper components of the lantern.

Ben Purdy, a maker colleague, took my CAD data and adapted it to a vector drawing so he could make a replacement rib in acrylic using a laser cutter.

It looked even funkier than the 3D printed rib, but the acrylic rib fit the lamp so neatly that it could have been used to make a perfect repair.

Ben turned up the intensity of the laser and cut another replacement rib from solid wood.

The laser charred the sides of the wooden rib, which makes it a nice match for the original wood in the Japanese lantern.

The laser didn't touch the top edge of the rib, so it's still pale.  But Ben can choose to apply stain and lacquer to make it a perfect match if he chooses.  Although the 3D printer didn't manufacture the final replacement rib, it was a helpful catalyst for completing the project.

It was certainly a fun, satisfying project.  Ben Sherwood shared it in a five-minute standup presentation at Ignite TAO PDX at the Alberta Rose Theater in Portland, which they recorded for posterity...
http://www.youtube.com/watch?feature=player_embedded&v=Tim3PSv5GrQ#t=305

Success 3 - Guile in the Box

Partial-spoiler warning: This blogpost does not disclose the solution, but for the sake of discussion it discloses history and design details that could spoil some of the surprises, especially for avid puzzlers.

Guile in the Box was my first-ever entry in the Nob Yoshigihara Puzzle Design competition, another personal landmark.  The challenge is to fit the four pieces into the box and shut the lid.  The four pieces are almost identical--each has an off-center notch, but one piece is a mirror image of the other three.  The box at rear left shows how three pieces (white) nearly fill the box, so the fourth piece is attached to a storage hook on the outside of the box.

Inspiration came from the 4-T Puzzle, an elegant challenge to fit four T-shaped pieces into square openings of two different sizes.  It's trivial to fit the pieces into the larger square, but the smaller one requires an "Aha!" insight.  The 4-T Puzzle is currently sold by ThinkFun.

Bits & Pieces sold a derivative called T Party, which extended 4-T Puzzle into a 3-dimensional puzzle by transforming the tray into a box with a lid, and by replacing the four T-shaped pieces with extruded aluminum segments.  The red pieces are cut from aluminum T angles.  Unfortunately the stock-sized aluminum didn't have the right proportions for this puzzle, so T Party has a number of unintended solutions other than the elegant one the designer intended.

Over time I grew dissatisfied with T Party because so many people who attempted it found inelegant solutions: arrangements that fit entirely inside the box, but didn't resemble the intended solution.  And it didn't exploit its three-dimensional design to accomplish anything new.

So I devised another three-dimensional adaptation with careful attention to all the specific ratios of height, width, and wall-thickness that would be required to replicate the behavior of the T-pieces in a square box.

I wanted the pieces to fit inside the box like they had in 4-T Puzzle, but I wanted there to be an added twist: that shouldn't be the solution to the puzzle!  But how to accomplish that?

Gotcha!  It's impossible to put the removable lid on when the pieces are arranged in the 4-T configuration because the pieces block access to the corner where the lid attaches to the box.  Users briefly think they've found the solution, but they can't close the lid--which unambiguously tells them they need to try something else!

To keep things interesting the asymmetrical pieces can fit together in various neat ways, but they can't all fit together the same way because one piece is a mirror image of the others.  I took advantage of a lot of testers' feedback while developing the puzzle, and tuned the pieces so they can fit and interlock in all sorts of fascinatingly distracting configurations.

The strange combination of pieces (3 left-handed and 1 right-handed) led many testers to think they'd gotten a mismatched set.  I embossed letters A, B, C, and D onto the four pieces to provide a visual confirmation they were correctly matched.

At the design competition Guile in the Box was exhibited adjacent to Tom Jolly's Little Window, another 4-piece packing puzzle handsomely crafted from manzanita and zebrawood.  Above, puzzle enthusiast Bram Cohen is trying to fit together Little Window after he'd already finished Guile in the Box.

[EDIT] As the founder of Bittorent Corporation, Bram Cohen got a bit of nice press today here.  It's so nice how well-connected everything is in the puzzle domain!

Success 2 - Its' Nuts!

In May I blogged how I built an enhanced copy of Oskar van Deventer's Cooksey Tribute D puzzle.  Oskar already owned a copy of Cooksey Tribute D, and so did I, so Oskar suggested I send the third as a gift to Jerry Slocum, a renowned puzzle enthusiast and author.

Coincidentally two other puzzle enthusiasts, John Rausch and Tyler Barrett, had recently persuaded me to build a small quantity of bolts with trick nuts like the ones in my Wrong Way Nut video so I chose to send one to Jerry.  That way Cooksey Tribute D would be a gift from Oskar, and Wrong Way Nut could be a gift from me.

For reference, here's the Wrong Way Nut video:

Jerry telephoned me immediately after he'd received the puzzles and asked if I could possibly build 120 copies of the bolt and nuts for the Puzzle Party.  I was thrilled!

We agreed the puzzle needed a name because I had originally adopted "wrong way nut" as a descriptive phrase, not an actual title.  Jerry researched to ensure we wouldn't infringe any trademarks.  I liked his suggestion Its' Nuts because it used an apostrophe in a nonstandard way, which was a subtle puzzle in itself.  Had it been intended as the contraction It's Nuts or a possessive term Its Nuts?

Each nut is embossed with "Its'" on one side and "Nuts" inverted on its opposite side so the puzzle's title appears when the nuts are correctly threaded onto the bolt.  Can you work out the probability of correctly assembling the bolt and its nuts so they say Its' Nuts?  (It's not just 1 in 2, as you might guess.)

It's customary for entries in the Edward Hordern IPP Puzzle Exchange to carry the name of the person exchanging them and the date of the IPP event when they were exchanged.  The bolts I built for Jerry are custom-embossed with IPP32 and the year 2012 on one face, and From Jerry Slocum on an opposite face.

With Jerry's approval, I added my own name to the top of the bolt head to identify myself as the creator.  Pay attention to how thin those letters really are, forming narrow strokes less than 1mm thick.

I deliberately made those hollow areas are narrower than 1mm so they wouldn't be sufficiently wide for the SD300 to apply anti-glue inside those narrow channels.  Consequently the letters are glued into the solid bolt head when the SD300 builds them, forming subtle outlines that can only be read by carefully examining the sheen of the top surface.

Screw threads need a slick finish, but the SD300 ordinarily builds layers with sharply-defined edges so I dipped every single nut and bolt in Weld-On 2007.

The solvent smooths and seals the layers, but after a few uses the solvent also tends to fog up the glossy top surface--an undesirable side effect.  To avoid fogging I learned how to dip the bolt only up to the sides of the hex-shaped head, but that left the side walls of the bolt head with a half-glossy/half-matte appearance.  The solution?  I wiped the side walls with ordinary PVC Pipe Primer from my local plumbing supply--it contains just enough solvents to impart a uniformly glossy appearance, and it includes a neat applicator.

This was a big project.  It took over a week to build all those bolts, and almost two weeks more to build all the nuts.  The nuts were more trouble than the bolts because I had to manually clear 72 layers of leftover support material from the center of each nut, tearing out the layers with a pointed probe as illustrated in this previous blog post.  It went at least twice as fast if I heated the model in my microwave oven for 30 seconds, a tip I learned from Jason Harris.

After the various pieces had been built, I assembled them into completed Its' Nuts sets.

I vacuum packed the bolt sets in groups for convenient shipping to Jerry.

For their final presentation Jerry repackaged Its' Nuts into individual prescription-drug containers, playfully labeled Slocum Pharmacy.  It included a caution, "Be sure to take with 1 grain of salt."

Jerry Slocum increased his order to 135 sets of Its' Nuts and I managed to build all 135 of them without any rejects or second-quality parts.  I sent him every single bolt I had built with the custom "From Jerry Slocum" inscription, and I forgot to keep one for myself!  I'm happy to build more bolts, but I wouldn't allow myself to build any more of Jerry's bolts--I regard them as a work-for-hire.

So I negotiated a puzzle-swap: he traded me one of the customized IPP bolts and in exchange I gave him this one-of-a-kind bolt that was professionally built via SLA, polished, and lacquered by a professional bureau.  To commemorate the occasion, I paired it with the very first nuts that had ever been inscribed with Its' Nuts.

Epilogue...
Jerry Slocum won me over to the name Its' Nuts because the odd placement of the apostrophe struck me as a clever piece of word-play.  He later confessed that it originated as a typo.