I would like to share my experience in making of the missing buttons for my Yamaha YIS805 MSX computer's keyboard at home. The goal of the project was to create the authentically looking buttons that would be sturdy enough to me changed several times and that would feel similar to the original buttons.
First, the buttons were made on the FDM printer. The result was not satisfactory because of the low resolution of the printer, too complex form of the buttons and the small text that could not be printed well enough. Failed.
The form for molding the buttons was designed and printed on the DLP printer. The form consisted of 3 parts that were assembled together and then the liquid UV-hardened plastic was poured inside. After removing the bubbles the form was exposed to UV light that was supposed to create the button inside it. Failed and resulted in a mess. The form leaked through very small gaps and the plastic inside didn't harden at all no matter how long the exposure was. The form got sealed from the outside as the result of the leak and disassembling it was no longer possible.
Then the buttons were fully made on the DLP printer. The result was partially satisfactory - the text could be easily read, but the buttons were too hard to fit properly onto the pushers and too fragile in their thin parts to be changed multiple times. So failed.
The buttons were separated into 2 and 3 parts - the outer part and the inner part(s). I started with the 2-component button. The outer part was printed on the DLP printer and the inner part was printed on the FDM printer. Then the parts were merged with the help of the instant glue. That method created the good resolution for the text, slightly flexible and sturdy placeholder for the pusher. The gaps for the letters were filled with the liquid UV-hardened plastic of a different color and the button was exposed to UV light from outside and from inside for a few minutes. Then the buttons were polished using the nail polisher stick (borrowed from my wife). The result was a success! The buttons look and feel almost like the original ones.
Trying the key on the real keyboard (but on YIS503 computer as I don't have the broken keyboard in my possession yet):
Final result after polishing:
The models of the buttons can be found in my Thingiverse repository:
https://www.thingiverse.com/thing:3446006
