I don’t want to dissuade you from buying a 3D printer but as for your pot lid knob, consider it will get hot and the knob will melt and run down over the pot the first time you use it. You might need to print a lot of knobs. 
I don’t want to dissuade you from buying a 3D printer but as for your pot lid knob, consider it will get hot and the knob will melt and run down over the pot the first time you use it. You might need to print a lot of knobs.