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:



  1. #1 by madbodger on 2016-06-24 - 09:38

    This sort of thing is where 3D printing shines. If they all do fall off, it would be simple enough to add a snap ridge on one or more sides.

    • #2 by Ed on 2016-06-24 - 09:44

      The layer lines probably serve the same purpose: I could feel it snap along the stud, repeatedly, as I pushed it on.

      In retrospect, I should have made a rectangular button with a domed top…

  2. #3 by Raj on 2016-06-24 - 23:26

    Ed, these push buttons come in a range of operating pressures. You could chose a type that suits your finger! I found out while trying to find a replacement center button for my mouse. Finally the PTT switch from a defunct FT411 did the job!

    • #4 by Ed on 2016-06-25 - 09:46

      You should see all the switches we didn’t use along the way! She started with a flat switch like the one on my bike, tried a few others, then settled on the peg you see here… and now we’re back to a bigger dome. All of them use the same mechanical design to get the sharp click we both depend on to verify that the switch activated: without that, we can’t tell when we’re on the air.

      One of these days I’ll spot a big surplus switch assortment and restock the bin!