Back last July another user VideoKarma use Resonance1 was looking for some phtos of knobs for Admiral 30A12 TV
http://videokarma.org/showthread.php?t=275980
I tried TinkerCad (free online web access) for the first time and created an initial 3D model of one of the knobs. I never finished the model but here is a snapshot of my admiral knob from my TV and the model I created with TinkerCad
Basically a cylinder resized and Rectangular box containing subdivisions. I created the 3 boxes across then created a duplicate and joined the two together. It was series of copies and joins. As I stated it was not finished. It could be created several ways. It seems TinkerCad mechanism for creating is similar to a mesh package such as Meshlab and Meshmixer. I didn't do any geometry. Maybe Resonance1 or others can give thoughts in a better way forward. Autodesk TinkerCad is free. All you have to do is create an online ID and start creating.
https://www.tinkercad.com/