Molding custom gaskets or O-rings?

--Ah. Well howzabout "casting" them in an open-top mold, using one of the curable rubber compounds?

First, I highly recommend the "bible" of oring seal design, the Parker handbook, for oring groove design to match your oring size. Online at

(Biggest mistake people make is to not make the groove a good bit wider than the oring so the material has some place to flow into when you crush it.) You could try injection molding using a caulking gun tube of RTV silicone - cheap to try, available at any hardware or building supply store, but it's going to be slow to cure even if you heat the mold up some. Might also get bubbles if you can't get the pressure high enough. Next choice in a castable might be polyurethane. My favorite vendor is but this comes up pretty often here and others recommend a couple of other vendors. Smoothon has some good online casting instructions, including pressurizing the mold with air at 100 psi to squash any bubbles while the stuff cures. They also have castable silicones but not in caulking gun tubes. You could also think about a version of Gingery's plastic injection molding machine, where you heat the mold but not the injector (for silicones and polyurethanes), to get more injection pressure. His book also covers moldmaking, which would directly apply to your quest. If you want a round oring you will need to ball mill the two halves of the oring into two facing plates that get bolted or clamped together. If a square or rectangular cross section is okay you could put the entire groove in one side and just use a flat plate for the cover - half the machining. You will have to experiment a little to find out how much shrinkage you will get (your orings will be a little smaller than your groove dimensions). Like someone else suggested, use a larger channel (sprue) to go from the tip on your caulking gun to the oring mold groove, and on the other side have a small vent path. Squeeze until it runs out, hope it filled both sides, and bake it at something like 200 F for a few hours (?) to quick cure it. Oh, smoothon sells a silicone spray mold release to use with the polyurethanes, and I think you can wipe on a thin film of vaseline as a mold release for the silicones.

-- Regards, Carl Ijames carl.ijames at verizon.net

goove should be wider at .177-.186 for a standard 1/8 inch oring

the depth [ crush direction ] should be shallower or about .100-.110 for a 1/8 inch oring

looser groove for a dynamic application , tighter for static

good ideas here ,

i would call loc-tite help line , i think their form in place stuff would be right up your alley , esspecially if you need a limited number

also you can try these guys , they have done a couple of tough ones for me.

Frequently in little $0.99 1/2 oz. packets at the auto store, for things like water pumps and thermostats where you don't need a lot. I'm sure the per application cost is higher, but I usualy have the rest of the tube turn solid in the toolbox anyway. If you dig for it, you may be able to find a case of the packets somewhere for less...? --Glenn Lyford

Sounds great. Where can I find more info on that, please?

Thank you.

Best,

Weyland

Excellent. Thank you. (upon trying to get it, it timed out - I'll try again later)

I'll check into them, thank you.

Great. Thanks. I'll order it up right away.

I'm not married to the o-ring profile, and for some odd reason find myself actually liking the square profile better. That, combined with your reasoning above, makes that seem the choice to pursue... I like the economy of effort presented by that flat plate.

I really like this idea... I could make a mold of say... 10 pieces that would easily fit in a household oven (read -shop oven) using the above flat plate mold, and rig up some way of pressure injecting the material into it.

Nice. Thanks.

Best,

Weyland

Errr... who?

Thanks,

Weyland

--Check out TAP Plastics if there's a store in your area; they've got a variety of stuff. Another source would be Devcon; they've got a zillion varieties of compounds, not just the metal-filled ones. Pick the Durometer you want and go shopping.

Thanks. No, no TAP stores down here. (Fort Lauderdale) I did happen to ask about Devcon (Loctite now) while in my bearing supply house today. Seems I was missing what the guys were describing when they were referring to the spray on type materials. They (Loctite/Devcon) did show some pictures of them in caulking gun type dispensers, so I'm somewhat more hopeful at this point. I'll call them tomorrow for more info.

Best,

Weyland