Double-shot moulding
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. Since then, production has been ultimately stopped and all keyboards with double-shot molded keycaps have been recalled. November 2011, German company GMK acquired the original tooling and molds[1]. In December 2011, EliteKeyboards offered the first GMK product in the form of a double-shot Cherry Escape key[2].
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[3]. 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.
Gallery
Back of Signature Plastics double-shot keycap production sample
The first shot, a white legend prior to molding
Front of Signature Plastics keycaps after the second shot
Back of keycaps after the second shot
Acorn BBC Microcomputer keyboard showing the bold, high contrast double-shot legends
BBC Micro spherical keycaps showing the characteristic patterning of the second colour
References
- ↑ Deskthority - German company GMK does MX 2shots
- ↑ Deskthority - EK selling authentic cherry doubleshot esc
- ↑ Deskthority – Visited Signature Plastics for real
