Customizable Knob for CPAP

This is a customizable knob to fit a D-shaft (shaft with flat) for a control that rotates and has push-on, push-off.

The housing it fits into has flats and ridges that interfere with pushing, and with the diameter of the print that holds the metal shaft.

I measured with digital calipers and wrote the openSCAD to model the broken knob, but better - stronger.

After an initial print that didn't fit, I added an option to the customizer to just print a test shaft so I could iterate on getting the dimensions right.

For the final print, I told the slicer to use concentric circles for the bottom layer - that's what you see in the finished print, in place on the CPAP.

In the slicer, I used a modifier to make the inner shaft use 4 vertical shells. That made it print solid, for extra strength.