Thursday, December 6, 2018

Finished CAD modeling of DSKY substitute keyboard


Cutting slots in honeycomb component

I finally got the hang of Fusion 360, which I have been learning this week to accomplish this task. Or at least, I have enough of a comprehension to finish the complex honeycomb component in which the button plungers slide up and down.
Plunger that sits over pushbutton and slides down honeycomb slots
The plunger is a .81 x .81 x .4 inch hollow translucent plastic piece with two guide tabs on the sides. These will slide inside the walls of the honeycomb in a slot that retains the key surface just below the faceplate edge while the plunger is at one extreme and allows the plunger to move downwards 1/4" to the other extreme. 
Honeycomb that guides the plunger and sits on PCB
Inside the plunger is a coil spring that couples the inner face of the plunger with the top of a pushbutton that is installed on a printed circuit board below. The spring will be selected to compress about 0.170". The pushbutton itself will move downward 0.0785" thus the combined movement is the target 1/4".
Example keycaps to fit over plunger
Since the pushbutton requires 21 ounces to move down, and the spring will have a resistance of 3-5 ounces, the combined force will be right in the range of the real DSKY key. The keycap is 1/16" thick and will be glued onto the face of the plunger. The plungers are snapped into the honeycomb slots and have their coil spring epoxied to the hole in the bottom.
The honeycomb structure and the PCB with its pushbutton switches are sandwiched together, threaded through with four screws that fit through standoffs below the PCB and thread into the aluminum base of the DSKY enclosure.
Model of the PCB with the 19 pushbuttons mounted
The honeycomb can be any 3D printable material that is sufficiently accurate and strong enough to hold together the switch assemblies, but the plunger itself must be a translucent plastic material to guide light from tiny LEDs on the PCB up through the cutouts on the keycaps.

I was finally ready to prepare the two 3D printing files. The honeycomb cost me $120 in fine detail plastic. The 19 translucent plastic plungers will cost roughly the same. Shame we didn't have a 3D production house sponsor as well.


  1. It's not obvious to me how the plungers will be inserted into the honeycomb, especially the central wells. It does not appear there would be enough flexibility in any of the components to allow insertion.

    1. Yes, I too am concerned about that. I won't send in the plungers until it is sorted out. Thank you for the alert - if I hadn't recognized that I could have had parts that couldn't be assembled.