Datanetics DC-60 is a family of tactile mechanical keyboard switches introduced in 1973.
The tactility of production DC-60 switches is neither well documented or well understood. Sandy’s page on the Fluke Y1700 keyboard suggests that the switches are linear that have become rough with age (neither Google nor Bing machine translation is sufficiently accurate to be sure), but it remains possible that the switches are faintly tactile and that Sandy simply didn’t realise that the tactility was intentional.
Meryl Miller sent me two assembled DC-60 switches: DC-61-03 (medium height tactile) and an unidentifiable linear DC-61-01 variant. From his time working at Datanetics, Meryl does not recall them ever selling linear DC-60 switches, yet he saved a sample of such a switch. By comparison, DC-61-03 is one of the most tactile switches I have encountered.
Additionally, I bought a bag of unidentified DC-61-01 variants from China, this time weakly tactile.
I had an x-ray taken of Meryl’s two switches side-by-side, and to no great surprise, they are visually identical inside:
(They were probably meant to face the same way, but the x-ray process ended up far harder than expected, with this being one final attempt at getting it right.)
The tactility appears to come from the normal force of the movable contact against the separator bar, but these parts are still present in the same form in the linear switch. As such, the linear switch should be tactile, but for unexplained reasons, it is linear. As this is the only one of its kind known to exist (and no other highly tactile examples are known to have been found), and as they are sealed shut, it is not possible to take direct measurements of the internal parts.
Through talking with Meryl, two possibilities have come. Datanetics engineer Mike Muller had apparently been experimenting with the cross-section shape of the separator bar. While this may affect the force exerted by the movable contact on the separator bar, from the x-ray image it appears that the two switches have circular cross-section separator bars, just as with all examples where the internals have been examined.
There are effectively three forces acting on the slider: the downward force from the operator’s finger, the upward force from the return spring, and the force from the movable contact. If the movable contact applies a horizontal force, then all it introduces is friction. If however it applies a diagonal force, then it will make the switch either lighter or stiffer depending on whether the force is diagonally upwards or diagonally downwards.
If you place a step in the movable contact, and the force changes mid-travel from horizontal to diagonally downward, it will suddenly counteract part of the return spring’s force, making the switch temporarily lighter. As such, the level of tactility will be related to the stiffness of the return spring, the shape and size of the step, and the stiffness of the movable contact.
This leads to the other possibility, that it is the movable contact that is sufficiently softer that it applies less diagonal force.
Sometime around 1979, it appears that Hewlett-Packard commissioned Cherry to produce a switch with the same dimensions as the tallest DC-60 type. This Cherry type is M1 (or M11). As M1 is linear, the suggestion is that the DC-60 switches in HP keyboards were also linear. (While linear is proven to exist, so far no documented evidence for it has been located.)
Meryl Miller provided two separate DC-60 brochures. These have been donated to the National Museum of American History Library who provided higher quality scans.
- Datanetics DC-60 series on the Deskthority wiki for prior notes and illustrations