Trapped Button Caps

In order to offer access to the buttons soldered to the TIMESQUARE PCB, I decided to build printed "caps" to extend the button press beyond the watch body. To keep the mechanical complexity low, I added a base to the button that would prevent it from falling out of the narrow button cavity, and scaled it down to compensate for more than the usual tolerance factor so that the button cap would sit in its cavity loose enough to move, but not enough to rattle.

Previous attempts to construct the buttons were too fragile, both in terms of the width of the shaft (shifting from 3.5mm to 5mm) and infill density (rotated the direction of infill and printed at 100% infill). I came to the result that worked through trial and error, taking notes each print as to the ideal height of the shaft, width for base, and shape of the grooves around the base to prevent rattling. 

Wireframe Routing Tip

One challenge for the base of the button was how to make sure the button functions well when pressed from any angle without either hitting the edge of the PCB (preventing the printed button cap from hitting the button on the board) or rattling. 

To help me solve this problem, I activated the layer that had the dummy cutting tool (ie larger than the printable dummy part) and to start the button cage and used the button that I had modeled on the dummy to help me find an angle satisfying my conditions.

Creating Button Cage

In the previous step, I used the dummy cutting tool model from a reference layer to calculate the furthest distance that the button might be expected to extend, with tolerance factors included. I created an ellipse at the angle I wanted for striking the button on the PCB, with enough range around the button the ensure good contact. 

Even though I wouldn't be using this closed curve to create a solid, I kept this ellipse throughout the design process as a reference point (and reference angle) to start when create the series of buttons I tried before selecting this simple shape -- building the buttons from the center of the ellipse and making sure that they satisfied the button's mechanical needs.

Creating Buttons and Button Cutting Tool

The yellow highlighted item ghosted within the larger outer button demonstrates the scale difference between the button cutting tool (the larger button) and highlighted button (for export for printing). Because these items are so small in terms of the roughly 0.5mm threadwidth of this machine, it was essential to keep the models handy for the cavity in a pre-boolean state so that the shape of the cavity and the shape of the button cap could be adjusted.

Printing Button Tests

For any part of a project that will be handled by a user, it is important to print lots of tests and record feedback for each version.

Within Rhino OSX I was able to generate mesh objects for testing the buttons. I collected each of the mesh results in row in a reference layer so that if the one-before-the-last-one proved to be the best, I had it ready.