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RAFI RS 74 M SPDT latching
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==Design== The shell appears to be identical to that of the illuminated switch, using the right-hand bay to hold a second terminal instead of an LED. The bottom of the shell is marked ".512" but this may be the shell part number, since the shell part numbers don't seem to correspond to switch part numbers. Based on small catalogue photos, the latch mechanism appears to be the same as that found in other RAFI RS 74 and RS 76 switches. Due to the size of the RS 74 switch, with the basic shell at 5.6 mm tall, or 6 mm including the standoff rails (half that of a [[Cherry MX]] switch) the latch mechanism must be very small. Unusually, it features a slide block; whereas [[Alps SKFL Lock]] places the cam track in the slider, this switch places the cam track in the slide block. The slider features a spring-loaded pin that follows the cam track. While Alps SKFL's follower pin is supported by a large plate spring, RAFI opted for a minute helical spring, 2.7 mm long and 0.9 mm in diameter, that sits inside the slider and maintains pressure on the follower pin. Following disassembly, the odds are very high that this spring will become lost. Until such time that regular RS 74 and 76 switches can be obtained for study, one may reasonably assume that the pictures here are representative of RAFI's latch mechanism. The contact system itself is also unusual. The normal RAFI flat metal loop is deformed in its normal state: the overhead stationary normally closed contact twists the loop down on its right side. As the slider is depressed, the left side of the loop is pushed down onto the stationary normally open contact, and then the right-hand side of the loop is twisted further to move it down away from the stationary contact. The action is fairly smooth and precise, with a clear tactile event. Nearly full travel (possibly just short of 2.5 mm) is required to actuate the switch: there is no clear overtravel. The switch contacts comprise flat gold-plated stationary terminals, and gold-plated hemispheres embedded inside the metal loop, with one hemisphere facing downwards towards the normally open contact, and one facing upwards towards the normally closed contact. The stationary contact terminals are strong, and are twisted by maybe 10Β° at the point of exit from the shell. The movable contact terminal is extremely weak owing to the particular thinness of the metal loop.
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