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How it is madeHanayama Cast Twist

by Oskar van Deventer

IntroductionHanayama cast puzzles are among the most coveted mechanical puzzles in theworld, famous for their perfection in all aspects. Initial production batches aretypically sold out within a couple of days, and many collectors worldwide maintain acomplete collection. This summer (2013), George Miller, Roxanne Wong, José and Imade a factory tour through China, visiting many factories and offices aroundShenzhen, Guangzhou and Hong Kong. Kyoo Wong of Hanayama spent a full day toshow us the Hanayama facilities. This article provides an impression of the manysteps that it takes to produce a Hanayama Cast Puzzle taking the youngest of theseries, Cast Twist, as example.

The puzzle designA puzzle design starts with an idea. After seeingmy Oskar’s Disks puzzle [1] from 1986, WilStrijbos suggested that the two disks should gothrough each other all the way. Hanayama Cast

Disk [2] from 2000 was one of the spin-offs ofthat suggestion. In 2004, shortly after GeorgeMiller introduced me to 3D-printing, I designedthe Snake Ball (see Figure 1), which Georgeprototyped on his machine [3]. We consideredthe puzzle impossible to mass produce at thattime, so we abandoned the project. Early 2012,Brett Rothstein asked me for a sample, which Idelivered via Shapeways [4]. I also provided asample to Teddy Sakamoto and Takeshi Onishiof Hanayama at IPP 2012. They would checkwhether Kyoo Wong could find a solution toproduce the puzzle.

Hand samplesThe first thing Hanayama does for a new puzzleis producing hand samples (Figure 3). Thesehand samples are machined from brass andserve to check all production details of thepuzzle. When a prototype is delivered in physicalform, like Akio Yamamoto’s organically shapedpuzzles, they are 3D-scanned so they can behandled by CAD software. As the Snake Ball

was already available in electronic form, thisstep could be skipped. Kyoo, together with aChinese CAD specialist, found a way to split theSnake Ball rings into three separate castableparts.

Figure 1. Snake Ball prototypeafter use by Hanayama

Figure 2. Hanayama’s3D-scanner

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Mould makingOnce the hand samples are approved, the mould-making process starts. Moulds arealso designed using CAD, see Figure 4. Special care is taken to make sure that thepieces can be extracted from the mould. First a negative of the mould cavity ismachined in copper (figures 5 and 6). Actually, there are multiple negatives as themould is made in multiple steps. The mould is made using a process called sparkerosion [5]. The copper negative is kept onto a steel slab that will become the mould,and a high current is put through the system. As a result, the steel is eroded awayspark by spark, and the minuscule sparks are washed away by a steady waterstream, see Figure 7. The process proceeds at a glacial speed.

Figure 3. First handsample of Cast Twist

Figure 4. Mould design

Figure 7. Spark erosion

Figure 5. Machining mould negatives in copper

Figure 6. Copper negatives

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Die castingOnce the mould is ready, a smallzero-series production run isperformed to test the mould. Themoulding process is called diecasting. A special molten zincalloy (Figure 10) is pressed intothe cavity of the mould, the zincsolidifies in the water-cooledmould, a robot arm grabs the stillhot cast and puts it on a slowly-moving conveyer belt (Figure12) to cool down. Once cooleddown, the sprue [6] is broken offand recycled (Figure 13).

Figure 10. Special zinc alloy

Figure 9. Kyoo, George andOskar checking the mould

Figure 8. Resulting mould

Figure 11. Molten zinc in hot die-casting machine

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Post-processingA lot of post-processing isneeded on the cast pieces.Hanayama use special ma-chines to cut off excess fleshfrom the cast pieces, cutthread, bend parts and more.The pieces are buffed [8] toremove any sharp edges (seeFigure 14). After some ma-nual checks, the pieces arepolished in a vibratory tum-bler [9], see Figure 16.

Figure 12. Die-casting machine with robot arm and conveyer belt

Figure 15. Kyoo sanding metal parts.

Figure 13. Cast parts on their sprue Figure 14. Buffing of the pieces

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Metal platingThe next step is metal plating[10]. Hanayama has manydifferent plating types availablewith different looks and proper-ties (Figure 17). Some platingsare extremely scratch resistant,whereas other platings providea nice antique look. Pieces fromthe zero series are tested withdifferent platings, and a mar-keting decision is made whatplating will be used for produc-tion. A complication is thatdifferent platings may have

different thickness, depending on the number of layers used. In some cases, themoulds need to be corrected to compensate for the change of thickness for adifferent plating choice. The accuracy is measured in micrometers here, and thesedifferences do matter in an ultra-high-quality product.

Assembly and packagingA lot of manual work goes into theassembly and packaging of thepuzzles. Whereas workers aretrained to quickly assemble apuzzle, they have no clue how totake it apart. Special care is takenduring transport and assembly toensure that the pieces do notscratch against each other, by indi-vidually packaging each part andassembly in its own little bag. Next,the assembled puzzles are strap-ped into their boxes (Figure 19),the boxes are put together and putinto larger boxes, which are collec-ted on pallets and moved into seacontainers for shipping (Figure 20).

Figure 16. Vibratory tumbler to givethe metal parts a smooth polish

Figure 18. Oskar, José and George holdingfreshly-plated metal parts (photographer

Kyoo is making a funny face)

Figure 17. Testing different metal platings

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Marketing, sales, toy fairs, distribution, shops, collectorsThe final step in the process is promotion and sales, which includes presenting thepuzzles at many toy fairs around the world (Figure 21). The puzzles are distributed tothe shops and sold to the collectors, who can then start solving the puzzles.

Hanayama, happy 30th anniversary!

References[1] Oskar’s Disks, http://www.gamepuzzles.com/prpuzzls.htm#OD.[2] Cast Disk, http://www.puzzlemaster.ca/browse/wire/metal/638-cast-disk.[3] Snake Ball, http://www.puzzlepalace.com/#puzzle=200410.[4] Snake Ball, https://www.shapeways.com/model/428387/snake-ball.html.[5] Spark erosion, http://en.wikipedia.org/wiki/Electrical_discharge_machining.[6] Die casting, http://en.wikipedia.org/wiki/Die_casting.[7] Sprue, http://en.wikipedia.org/wiki/Sprue_%28manufacturing%29.[8] Buffing, http://en.wikipedia.org/wiki/Buffing.[9] Vibratory tumbler, http://en.wikipedia.org/wiki/Vibratory_finishing.[10] Metal plating, http://en.wikipedia.org/wiki/Metal_plating.

Figure 20. Shipping containerfilled with Hanayama puzzlesFigure 19. Packaging the puzzles

Figure 21. Hirano demonstratingHanayama puzzles at Tokyo Toy Fair

Figure 22. Special multi-coloursample for Oskar