Double-shot moulding

Double-shot keycap production sample

Cherry announcement about double-shot keycaps

Double-shot molding, double-shot, dual-injection molding or insert molding is the process of molding plastic around a preformed metal or plastic insert. This has been a popular process to create very durable keycaps in the past. Recently, the process has become more rare and is usually only used on separate keycap orders from companies such as Signature Plastics or on special keyboards used as military or medical equipment. There currently is no mainstream keyboard being produced that still uses double-injection molded keycaps. Until early 2010, Cherry still offered double-shot molded keycaps as an option for their POS and special-order keyboards. Production ultimately stopped and all keyboards with double-shot molded keycaps were recalled. November 2012, it was announced that German company GMK had acquired the original tooling and molds. In December 2012, EliteKeyboards offered the first GMK product in the form of a double-shot Cherry Escape key.

Attributes

Advantages

• Maximum contrast lettering: the legends are bold and vibrant and pure in tone, with smooth edges and uniform colouration.
• Zero wear: the legend will never wear, as it runs right through the surface of the keycap.
• Colour freedom: the keycap and legend can each be of any colour desired: this lends itself well to custom keycaps where a wide range of colours is highly desirable.
• Feel: the legend and the keycap are one, and the legend cannot be felt while typing.

Disadvantages

• Cost and availability: the process of building moulds for each and every legend is an expensive process compared to making one mould per row profile and adding the legends afterwards on demand, especially considering manufacture for the wider international market where even simple letters such as "A" move between row profiles (e.g. QWERTY vs AZERTY, QWERTY vs QWERTZ).
• Single colour: typical double-shot processes restrict the keycap to a single legend colour, although it is possible to inject further colours and this has been done.
• Low resolution: double-shot legends are limited to low resolution designs with broad strokes and rounded corners. The range of typefaces and symbol designs available with pad printing and dye sublimation cannot be achieved with double-shot, as the moulding process doesn't support the fine detail and sharp edges that those processes afford.
• Gloss and yellowing: Double-shot moulded keys are made from ABS plastic because most other plastics shrink too much in the moulding process. ABS may yellow over time, and is not as hard as PBT plastic. The texture of PBT keycaps will remain longer than the texture of ABS keycaps - the ABS keycaps get glossy after extended usage. Because of this, PBT keys with dye sublimated legends are regarded by many as an even better alternative, although dye sublimation has its own set of disadvantages and limitations, most notably it cannot be used to print light legends on dark keycaps.

Production

As the name suggests, double-shot molding is a two step process. In the first step, the legend or graphics to be placed on the keycap, are molded in plastic. The plastic insert, resulting from the first step, is then placed in another mold, while plastic is inserted under heat to combine both molds to a single piece keycap.

Manufacturers

Companies who manufacture or previously manufactured double-shot keycaps include:

• Cherry (tooling now sold to GMK) — for Cherry switches
• GMK
• Tai-Hao — Cherry MX and Alps mount
• Signature Plastics — many mount styles

Gallery

Signature Plastics

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  Signature Plastics group buy novelty keycaps

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  Back of Signature Plastics double-shot keycap production sample

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  The first shot, a white legend prior to molding

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  Front of Signature Plastics keycaps after the second shot

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  Back of keycaps after the second shot

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  RGB modifiers

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  Assorted novelty keycaps

Alps Electric

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  Alps double-shot keycap from a NeXT keyboard (Alps SKCM Black)

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  Alps double-shot keycap on an Alps integrated dome keyboard

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  Assorted IBM 5556 keycaps, top view

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  Assorted IBM 5556 keycaps, underside, showing the different moulding patterns

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  Detail of IBM 5556 keycap

Tai-Hao

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  2013 product samples

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  Bottom view showing the moulding process

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  1991/1992 keycaps (top) and 2013 group buy keycaps (bottom)

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  Underside view

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  Assorted 2013 group buy keycaps

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  Cherry MX mount rubber WASD gamer keycaps

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  Top and bottom views of the rubber gamer keycaps

Other

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  Acorn BBC Microcomputer keyboard showing the bold, high contrast double-shot legends

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  BBC Micro spherical keycaps showing the characteristic patterning of the second colour (Futaba switches; keycap manufacturer not known)

External links

• tttっちゃtttttったりttttったいね — Yamaha QX3 Sequencer keyboard — quadruple-shot keycaps (Japanese)