Pourable Mold Material

What material can I pour into a 1" x 1" x 1" mold (a cube without a lid) that will solidify into a rubber-type consistency? I need to make a part for a microphone that has not been manufactured in 50 years. It would be best if the material did not harden like acrylic. However, I'd use that as a last resort if I knew where to get it.
I've never done this sort of thing, so I have no idea what material to try to find or where to search for it. Since I only need a small amount, a suggestion for a material that is only available from a wholesale-only industrial supply house would be hard to follow.
Is there some sort of silicone that meets this requirement? Is there such a thing as liquid rubber? Here's hoping!
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Use ordinary silicone rubber, build it up in layers or just fill the whole thing up at one time and wait a few days.
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On 4/29/2013 2:15 PM, mcp6453 wrote:

Silicon RTV adhesive or caulk would cure eventually but an inch is a little thick.
On the outdoor channel the other day I saw a guy having ear fitting ear plugs made by having liquid rubber injected from a syringe right in his ear so there is such an animal.
This mold builder stuff might work with enough coats:
http://www.micromark.com/liquid-rubber-32-fl-oz,7472.html
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I think silicone caulk would do it in about 3 days. [for about $5]
G-flex epoxy would give you more of a polyethylene plastic in about 5 minutes- for $20 or so from a boat store.
I'd give Devcon a call and see if they have a rubber 5 minute epoxy.
Jim
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Jim Elbrecht wrote:

If the part is to be greater than 1/4" thick, regular silicone caulk will not work since it will not cure properly. For thicker parts a catalyzed silicone material is required. Look at McMaster.com for various castable silicones, urethanes and the like.
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-snip-

After I found a tube of it solidified I played around with thicker 'pours'. An inch thick takes a couple weeks-- but 1/3 is close over night-- then another third-- and another.

I'll second the plug for mcmaster.com - though I haven't used any.
Jim
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replying to mcp6453 , DA wrote:

Tin-cure RTV silicon rubber sounds like the best material for this. Noone (I know) sells such small amounts for a 1" cube and besides, it will be really difficult to properly measure 10:1 ratio of components if you only need 1cu.inch. It is sensitive to proper component ratios. 1 cu. inch is usually more than I have leftovers after a mold is poured - this could have been easily done from someone's leftovers if you can find a sculptor or a builder or another specialist, artist or hobbyist in your area working with RTV molds.
Smooth-On sells very nice RTV silicons. I use mostly MoldMax 30 but it's pink - do you care what color it is? MoldMax40 is light green, and they also have translucent versions of all of these. Here is the page at their site about the silicones: http://www.smooth-on.com/Silicone-Rubber-an/c2_1113_1135/index.html
They do sell online, including trial size packages for about $25 but at 2.2 lbs it is still more than you need if you only need one of these cubes. Arts and crafts stores like Michaels also sell similar silicones (I think they are similar) but they are about 4 times the cost per weight unit, so I've never bought from a craft store, can't vouch for their quality or workability.
I guess for a small cube any RTV you can get your hands on will do, but for any serious work I'd use Smooth-on product.
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On 4/29/2013 11:15 AM, mcp6453 wrote:

there are many products that can be used. see
http://www.smooth-on.com/
i think hobby shops like michaels sells a 2 part curable silicone product that would do this.
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On 4/29/2013 3:49 PM, chaniarts wrote:

The smooth-on site looks like it may have a solution. There are some videos and helper guides there. Thanks everyone for the information.
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I found the trial size costs about $25 . Mold max 10 looks like plenty of goo for 1 inch square.
What I have used is sylgard.
http://www.ebay.com/itm/NEW-Dow-Corning-2-Part-Sylgard-170-Silicone-Elastomer-Kit-0-9KG-/181080928215?pt=LH_DefaultDomain_0&hash=item2a2943afd7
Greg
Greg
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replying to gregz , DA wrote:

Mold Max 10 is very soft - the hardness goes up with the number. I imagine the OP might need harder ones - 30 or 40 if this is used to hold any considerable weight firmly. It would be interesting to learn which exactly part of the mic would be made from rubber (-like material). Last time I've been inside old mics was a very long time ago but I cannot recall a large elastic part like that.
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I use to use silastic products, but costly.
You might try dynaflex 230 into a cube if silicone rtv does not work. I don't know how 230 will set up in a cube, worth a try. Heat it up for a couple days. Rtv should also set up with heat and time. It used to be easy to buy the runny stuff for windshields, but I have not seen it lately.
Greg
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On 4/29/2013 6:19 PM, gregz wrote:

Does it have to be all rubber? Can you mold most of it out of Sculpy and use sheet rubber for the springy part?
There's stuff called "Great Stuff" that's used for plugging up air infiltration in buildings.
The cheap stuff gets pretty hard. The more expensive version stays spongy. Can get it at Home Depot. Don't know if it has the mechanical strength for your application.
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The water based stuff is pretty spongy and porus.
Greg
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On 04/29/2013 11:15 AM, mcp6453 wrote:

Might think about plasti-dip, possibly pouring it in layers to help it set up faster. It's pretty cheap, too.
Jon
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Any craft store should sell silicone based molding material. Since you need such a small amount, save some time and shipping costs and just pick some up at a craft store like AC Moore, Michael's, etc. You won't be making a mold but you can use it to fill a small one.
Good Luck.
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