Casting Rubber Parts
 

So I have a variety of projects that need some rubber parts replaced. These are from a variety of appliances and run the gambit on condition - some are dried and broken into shards, others are intact, some are melting, etc. None can be found anymore, so I'm looking to have them reproduced based on the examples I have.

I talked to Ed Schutz, and he's unable to help me because of his workload. I've had him help me in the past so I know this is possible. Additionally, I've looked at some tutorials and the process seems like something I could do myself without any issue.

Does anyone have any experience casting rubber? I'm thinking of using silicone because it sounds like it lasts longer, but I haven't found a good source for what I need. Also, some of these parts are exterior, so I'd want to replicate the colors as closely as I could (cream and black, so thankfully nothing too bizarre.) I'm trying to find a good source for rubber or silicone that can be cast into the parts I need, probably using a silicone mold. I've seen flexane, but it looks rather expensive. Are there any cheaper options available? Admittedly I don't know much about the kinds of rubber available, so I'm not sure what would be best for these parts, especially since several are used as chassis or motor mounts.

Any advice or help on figuring this out is appreciated. If I can get this going, I'd be happy to keep the molds available to help everyone else out as well. Without undercutting Ed, of course.

Make: magazine had a nice tutorial on casting rubber and plastic items - "Adam Savage" from Mythbusters was the author. Mostly plaster cast of the old item, mold release solution, and two-part casting rubber for the actual item. The article had links to suppliers IIRC.

http://makezine.com/projects/make-08/primer-moldmaking/

Aside from the molding process, which I know little about, I'd say regular 100% silicone you get in tubes from the hardware store should work fine. Black rtv for automotive gasket making is good for a jet black color. Although a lot of automotive 'black' rtv is actually slate gray, look among the cheaper ones for actual black. I've looked into this a bit, but never actually attempted it - apparently if you mix corn starch with silicone (look on youtube for silicone mold making) it seems to change its cured form a bit, making it perhaps a bit firmer (and I imagine stronger), but without losing flexibility. And if you use clear silicone and corn starch, it'll become opaque and you can mix in paint to change the color.

If you need a firmer, stronger material (cured silicone is still kinda squishy), you could use automotive urethane (windshield glue). It's maybe $20 a tube, and a messy pain in the ass to work with (gloves mandatory), but the finished product is a lot like black vulcanized rubber, and it sticks better than anything, really. So for a motor mount, you could 'mold' a bolt into the urethane, and I wouldn't worry about it breaking off. I actually have an old typewriter that needs new rubber feet, that I've been thinking about doing this for.

Also don't forget that rubber can be machined. If you need a structural part (not decorative), try talking to a machinist.