Double-shot moulding

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Double-shot keycap production sample
Double-shot keycap production sample

Double-shot moulding, double-shot, dual-injection moulding, two-shot moulding or insert moulding is the process of moulding plastic around a preformed metal or plastic insert. This has been a popular process to create very durable keycaps in the past, used extensively in the 70s and 80s and still found into the 90s. Once a staple of keyboard manufacturing, during the 1990s double-shot moulding faded into obsolescence as keyboards were reduced to a simple commodity.

Double-shot moulding is enjoying a slow resurgence in the gamer and enthusiast markets: brands such as Vortex, Tai-Hao and Topre now provide modern backlit double-shot keycaps, and Tai-Hao double-shots are available for sale in a wide variety of colourways in both ABS and PBT plastic. These new product ranges demonstrate a willingness to invest in this technology.

Attributes

Advantages

  • Maximum contrast lettering: the legends are bold and vibrant and pure in tone, with smooth edges and uniform colouration.
  • Zero legend wear: the legend will never wear, as it runs right through the surface of the keycap; also, unlike engraved and laser foamed legends, dirt cannot accumulate within the legend.
  • 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 is fully flush with the keycap surface, and it 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.
  • Typeface limitations: double-shot moulding cannot provide the sharp corners that are present in most typefaces, which poses a minor limitation on the typography of legends
  • Gloss and yellowing: Double-shot keycaps are typically manufactured from ABS plastic. ABS may yellow over time, and it is not as hard as PBT plastic. The texture of PBT keycaps will remain longer than the texture of ABS keycaps: ABS keycaps become glossy with use. 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 that it cannot be used to print light legends onto dark keycaps. PBT double-shots are now in available, using a non-PBT plastic for the first shot.

Production

As the name suggests, double-shot moulding is a two-step process. In the first step, the legend or graphics to be placed on the keycap, are moulded in plastic[1]. The plastic insert, resulting from the first step, is then placed into another mould, and plastic is inserted under heat to combine both moulds to a single piece keycap.

The technicalities of this process vary quite distinctly between manufacturers. In many cases, the process leads to a striped pattern within the keycap formed from the two different coloured plastics. This striped pattern remains even when keycaps are manufactured for engraving or other marking processes, as is clearly visible with Devlin Q series keycaps.

Other manufacturers use a wholly or near-wholly solid first shot, that gives keycaps a "nested" or "stacked" appearance when viewed from below. Regardless of the specifics, double-shot keycaps can be identified by observing the underside where both colours are visible.

Double-shot moulding.jpg

Despite the name, the moulding process is not restricted to two colours: triple and quadruple[2] shot keycaps exist, where two or three different legend colours are present on a single keycap. The use of more than three colours is however quite rare. More commonly, where multiple legend colours are required, the additional colours are provided using pad printing (dye sublimation would be unsuitable with the ABS material used in double-shot moulding). This is especially true where the extra text is printed on the front of the keycap, such as with NeXT keyboards.

Materials

The majority of double-shot keycaps are made entirely from ABS plastic. Despite their greater wear resistance, Signature Plastics have confirmed that the majority of Comptec keycaps were nonetheless made from ABS, albeit of different formulations (the plastic formulations have since changed due to regulatory requirements).[3] Older Cherry catalogues show that in 1982, the tall Cherry M7 and Cherry M9 keycaps were made of double-shot Tenite, while their other double-shot keycaps were all ABS.

ABS is typically chosen because most other plastics shrink too much in the moulding process.[Citation needed] Modern ABS however lacks the desired wear resistance, leading to keycaps that develop shine too readily. However, PBT double-shot keycaps are now produced by both Vortex and Tai-Hao.

Backlighting

Double-shot moulding is suitable for backlighting: the first shot can be made from a translucent plastic. Vortex, Tai-Hao and Topre all offer backlit double-shot keycaps. In Topre's case, the first shot cannot support fully enclosed shapes, giving a stencil-like appearance.[4] Neither Vortex's or Tai-Hao's processes are affected by this limitation.

Manufacturers

Double-shot keycaps were a standard feature of many vintage keyboards, when keyboards were expected to be expensive. As a result, many manufacturers have produced double-shot keycaps. Only a small number of these product ranges are still known to be in production to this day. However, new product lines have arisen to cater for the gamer and enthusiast markets.

Current

Devlin

Devlin's Q series and K series keycaps are available in both double-shot and engraved forms.

GMK

Until early 2010, Cherry still offered double-shot moulded keycaps as an option for their POS and special-order keyboards. Production ultimately stopped and all keyboards with double-shot moulded keycaps were called off. November 2012, it was announced that German company GMK had acquired the original tooling and moulds[5]. In December 2012, EliteKeyboards offered the first GMK product in the form of a double-shot Cherry Escape key[6].

RAFI

Signature Plastics

Signature Plastics took over the keycap manufacturing of Comptec.

Tai-Hao

Tai-Hao are a long-time manufacturer of double-shot keycaps, both Cherry MX mount and Alps mount. Their widely-used TI series is still manufactured to this day, and has been extended to cover PBT keycaps. Tai-Hao keycaps were used by brands including Ortek, Focus Electronic and Northgate Computer Systems.

Tai-Hao offer opaque PBT, backlit ABS and backlit PBT double-shot keycaps.[7]

Topre

The Topre Realforce RGB comes with backlit double-shot keycaps. These are one of the product ranges that show a stencil look to the first shot.[4] While sold by Topre, it is not confirmed that Topre manufacture the keycaps themselves.

Vortex

Vortex are one of the manufacturers of PBT double-shot keycaps. Vortex backlit keycaps use translucent POM for the first shot, and PBT for the second shot.[8] Vortex also offer non-backlit double-shot PBT keycaps.[9]

Historical

Alps Electric

While Alps are better known for the dye sublimated keycaps used in Apple keyboards, Alps also produced distinctive double-shot keycaps. Alps are one of the companies whose moulding process did not show stripes of colour within the underside of the keycap. Many double-shot Alps keycaps feature a curious pattern of bars and square holes that aids in their identification.

Alps double-shot keycaps are likely to have been produced in-house.

Cherry

Cherry announcement about double-shot keycaps

Cherry produced double-shot keycaps in-house, they discontinued the manufacture of double-shot keycaps in 2011. The tooling was sold to GMK, who resumed manufacture of the parts.

Comptec

Comptec were one of the world's leading keycap manufacturers, whose keycaps have been found in a large variety of equipment including the Acorn BBC Microcomputer and Wyse terminal keyboards. Comptec USA became Signature Plastics, who remain a very prominent double-shot manufacturer. Tall Comptec keycaps often feature an inner step that appears to be specific to their manufacturing process.

Futaba

Little is known about Futaba keycaps.

Micro Switch

Micro Switch are notable for their very thick, sturdy keycaps.

SMK

SMK double-shot keycaps have varied in design over time. All their keycap styles have in common a completely solid first shot, without striped bands of colour. Older keycaps (from SMK vintage linear keyboards) had a large first shot (giving thick keycaps), while newer keycaps for SMK second generation switches reduced the size of the first shot. It is not known whether they were produced in-house or outsourced.

External links

References

  1. Deskthority — Visited Signature Plastics for real
  2. Deskthority — Quad-shot keycaps?
  3. Correspondence with Signature Plastics, 2015-10-02
  4. 4.0 4.1 Deskthority — [Review] Realforce RGB
  5. Deskthority — German company GMK does MX 2shots
  6. Deskthority — EK selling authentic cherry doubleshot esc
  7. Tai-Hao — Products
  8. Massdrop — Vortex Backlit Doubleshot PBT Keycaps
  9. Mechanical Keyboards — Blue - Bi-Color PBT Double Shot Keycap Set by Vortex