I would like to start making my own rubber feet for antique typewriters and was needing advice for which product to use. Thank you, Jay
That sounds like a little hockey puck shaped thing with hole in the top that has a profound undercut to receive a flat metal part of a typewriter. The approach should depend on how big the part is, and how many copies of each part are called for, and how profound the undercut is, and whether I had one original rubber foot to start with, and whether I had a copy of the metal part of the typewriter that the molded part attaches to.
I'd use a 2-piece rigid Urethane mold (RC-3) and I'd pour a silicone that was more firm than Plat 40 for the parts. If the part on the typewriter that the foot fits to is a very flat metal disk, you may need to mold the part around such a metal disk, if not an actual typewriter foot, rather than letting that geometry be defined by a mold made of the RC-3.
I'm picturing a black part. You might get away with cheating with a dye meant for urethane www.alumilite.com/dyes-colors/alumilite-dye/, but don't tell anybody I told you to do that. I say this because it's a lot easier to work with; adding drops instead of weighing paste. I've done it with clear platinum-cure silicone in the past, but the needed color was not intense at all.
Make an account and share some pics of the molded part and the component the part grips to.
You could use one of the Flex series for the feet. It's got a rubber texture but is still a resin type. And it can easily be colored with the resin dyes. I use the Flex for custom rubber stamps and it should have no problem being hard enough to hold the weight but still have the right texture.