APRS/GPS + Voice Interface: Improved PTT Button Cap

Long ago, Mary picked out a PTT switch with a raised, square post that provided a distinct shape and positive tactile feedback:

PTT Button - bare post
PTT Button – bare post

Time passes, she dinged her thumb in the garden, and asked for a more rounded button. I have some switches with rounded caps, but replacing the existing switch looked a lot like work, sooooo:

PTT Button Cap - Slic3r preview
PTT Button Cap – Slic3r preview

As with all small objects, building them four at a time gives the plastic in each one time to cool before slapping the next layer on top:

PTT Button - on platform
PTT Button – on platform

The hole in the cap is 0.2 mm oversize, which results in a snug press fit on the small ridges barely visible around the post in the first image:

PTT Button - rounded cap
PTT Button – rounded cap

Rather than compute the chord covering the surface, I just resized a sphere to twice the desired dome height (picked as 6 threads, just for convenience) and plunked it atop a cylinder. Remember to expand the sphere diameter by 1/cos(180/sides) to make it match the cylinder and force both to have the same number of sides.

If it falls off, I have three backups.

The OpenSCAD source code as a GitHub Gist:

// PTT Button cap
// Ed Nisley KE4ZNU - June 2016
//- Extrusion parameters - must match reality!
ThreadThick = 0.20;
ThreadWidth = 0.40;
Protrusion = 0.1;
HoleWindage = 0.2;
// Dimensions
Post = [3.8,3.8,3.0];
OD = 0;
Button = [12,0+Post[2],6*ThreadThick];
NumSides = 8*4;
//- Build it
difference() {
union() {
translate([0,0,Post[2]/2 - Protrusion])
cube(Post + [HoleWindage,HoleWindage,Protrusion],center=true);