RAFI RS 74 M
 | |
| Manufacturer | RAFI |
|---|---|
| Family | RAFI Full-Travel Keyswitch |
| Introduced | 1975 |
| Discontinued | 2005 |
| Switch type | Linear, latching lock |
| Sense method | Metal leaf |
| Actuation force | 80 cN |
| Total travel | 2.5 mm |
| Keycap mount | RAFI |
| Switch mount | PCB |
RAFI RS 74 M is a low-travel switch in the RAFI Full-Travel Keyswitch family.
Contents
Description
RS 74 M switches share the same overall design as the 4 mm RAFI RS 76 M switch, but have a reduced travel of 2.5 mm. They are targeted at a unit of 0.75", or 19.05 mm, and the switch shells are themselves this exact width.
The switch uses a square loop of sprung metal that is kept away from a metal contact by the slider. When the slider is depressed, the metal loop lowers until it reaches the static contact. The switch has two solder points, and the slider recess appears to form the single PCB fixing pin. Actuation is at 1.5±0.5 mm; the lug on the slider which raises the loop travels further than the loop drops.
The sprung loop and the static contact both feature gold crosspoint contacts, as with most Cherry switches.
The switches are available in several forms: linear, linear (illuminated), latching, and latching (illuminated). So-called "illuminated" switches simply have room for an LED in the top-right corner; they are not intended to provide backlit keycaps.
Keyfeel
RS 74 M switches appear to be intended for keypads, not desktop keyboards (for which, you would use the RS 76 M or RS 76 C); they have an actuation force of 80 cN within a pretravel distance of 2.5 mm, which makes them quite stiff. Based on a 1984 keyboard, they can also suffer from binding when struck at the corner.
Keycaps
QWERTY keycaps are double-shot; other legended keycaps are engraved and painted; RAFI's catalogue suggests that the engraving is not performed with a laser, as the infill process is not stated as being applied to lasered keycaps, only the "labour intensive" low volume engraving process. Relegendable keycaps are also available.
Variants
Linear
The basic linear switch has a clear plastic top.
Linear (illuminated)
The illuminated linear variant has space at the top-right for an LED, and the clear plastic top to the switch is absent. There is a recessed area at the rear of the shell which appears to be designed to support the latching mechanism in the latching variety.
The slider on the linear version has two lugs that sit above and below the sprung loop; when the switch is fully depressed, the loop is forcibly deformed, unlike the non-illuminated version where the loop is only raised by the slider on the return.
Latching lock
Latching lock (illuminated)
Keyboards
- Neve Necam 96 audio workstation keyboard
- Thorn EMI Liberator keyboard[1]
Status
RS 74 M switches were discontinued from production in 2005, but they are still available as replacement parts with a minimum order quantity (MOQ) of 25 pieces.
Gallery
RAFI RS 74 M switches
RAFI RS 74 M switches
PCB traces
Opened switch
Opened switch viewed from the rear
Slider, spring, upper shell
Upper shell is hard to remove without damage
Gold crosspoint prism on the static contact
Gold crosspoint prism on the sprung contact
Slider fully depressed
Linear illuminated variant; the switch design is open and has no transparent top
Slider removed
Spring removed from the slider
RAFI keycaps targeted at the RS 74 M
References
- ↑ The Register — Liberator: the untold story of the first British laptop part 1 (page 4)
