The knob of our 2003 Honda Odyssey broke so, rather than take the easy way out with a replacement, I decided to design and print a replacement in the classic "chicken head" design dating back to the '50s.
Obviously, a little finishing work (i.e. sanding) is due and then some paint. I think I'll paint it black with a thin stripe on the "beak" so the backing light will be visible through the off-white PLA.
I'd like to make another but I also have concerns about the PLA getting too soft on a black dashboard in the hot sun. So I'm planning on making a silicone mold of this printed part so I can cast it in resin and have a version that will be be able to better withstand the heat of a car interior. This will be interesting, I've never done a two-part mold of a 3D printed part, only open-faced molds of a couple previous projects.
Once that's done, I'll paint and stripe the cast ones for permanent use.
Now that the model was just right to fit the car functionally, I could have some fun trying to adapt the classic "chicken head" design within dimensions that would work well in the car and printed it out.....
I found that the printed knob was *very* accurate except for the inside D hole, which printed about 6% too small, probably due to the natural "squish" of the PLA. Back in 123D Design, I expanded the hole by this amout and, to save time, I printed only that part of the model - it fit perfectly!
Having not designed an original mechanical part to fit onto a commercial product, I used my calipers to measure every dimension of the original knob where it interfaces with the car - the shaft receptacle and the proper circumference lip design. The top at this point was just a simple stand-in. I printed this as a proof-of-concept for the basic functional design and to prove that my 3D printer (Flux 3D Delta) could give me the accuracy that this project needed.