I’ve been on a platen knob hunt lately. My interest in making platen knobs has peaked as several machines have come into the shop with broken and missing knobs. I buy many 3D printed knobs and continue to encourage folks to produce and sell them. I’ll keep buying them!
For the knob that doesn’t fit the 3D mold (ha, ha) I make my own by forming silicone molds. These are from original knobs that are as perfect as 80 years plus of aging can make. Today I finished making silicone molds for both the Corona portable model 3 right side knob and the left and right side knob for the Corona portable model 4.
Knobs are $10 each. You send the metal core with what ever remnants are attached and I match the color as close as possible (think Bruce Green). You get back an acrylic plastic knob that is pretty hard to tell from an original.