Count yourself lucky if you own a Hermes 3000 and your knobs are in good shape I have two of these typewriters that are in fantastic shape and all knobs, levers, and buttons are extant and operable. However, I do have one Hermes that is missing both knobs.
It's a lovely mid-body Hermes. You know the ones; pale green and white key tops. They have all the feel of the original Hermes with the extra brittle knobs. Bonus! I haven't put it out into the rotation because of the knobs. As a typer it's completely useable, but the knoblesness makes loading paper too dependent on the line spacing mechanism. So, I set out to make a new knob.
Rob made some out of wood. Very nice. I support hand-crafted lovliness. Wood would be good, but plastic...well the future is in plastics. I, however, do not have a plastics factory. Or do I?
Enter Instamorph. You may have seen it as Shapelock or (as the boffins in labs know it) Polycaprolactone; PCL. This plastic is amazing. It melts in 60 degree (140F) water and becomes a pliable putty that you can mold into a variety of shapes. Apart form the hobbyist applications, there are medical uses (drug delivery systems) that make this a very unusual material. I like it because you can make into typewriter knobs.
I took the original mandrel from the Hermes knob and cleaned it off. I then melted some PCL according to the directions on the tub and started forming the small lump into something that resembled a typewriter knob. I worked the material over for a while trying to make a close fit to the mandrel. The material is pliable, but it can be stiff and I was having a hard time making a tight fit around the part. I then thought to form the piece slightly smaller and compression fit it into place. That worked marvelously. In the end I got this.
It is a good size, but looks a little homemade. If you have a little more time and a little more ambition you could make it look a lot better. I gave the plastic some time to cool and then attach the newly-crafted knob to the typewriter. The best thing about this plastic is that if you are unhappy with the outcome, just cut it up into little pieces and reheat it. This process can be done over and over. It's really a great/fun material to work with.
Time will yield results on the long-term durability, but I have high hopes. Instamorph (and Shapelock) are paintable. There might even be possibilities in making (or remaking) feet, keytops, and bushings; anything you might imagine. Now, there is one caveat; Instamorph is biodegradable. So that knob or foot or keytop might not last for decades, but it's perfect for fairly fast repairs.
Instamorph: http://www.instamorph.com (Distributed by a local company out of Scottsdale, AZ)