molding with rubber

[Gordon T Haley]

I'm thinking of doing some resin casts from a rubber mold. Looking for info is hard ,most info I find is from manufactures websites. I would like to know info from users. Does anyone here make and use rubber molds?

[Tony Castronovo]

Gordon, Hello Tony here... I know I haven't been to talkative lately I have been busy building our new house, and I feel every bit of my 52 years of age on this one. I have allot of experience with casting and rubber (silicone) molding. My email is the same and I can help get you started and even find a couple of our old suppliers. It is not hard, however it is not inexpensive material, and if the molds are not abused you can make hundreds of parts out of a mold. You need to find a pressure pot, depending on the size of your molds will depend on the pot size. In your case I guess you are going to make small engines? You can probably find a 5 gallon pressure paint pot. It has to be able to hold a constant 80 pounds of pressure ( not vacuum ) safely. You will also need a small compressor, maybe 1.5 HP is fine in your case.
We use to make ( BC ) super high quality parts for IMEX in the form of 12" resin figures that retailed as much as $100.00 each. The details we were able to get were museum model quality with a 98% product manufactured. You can not afford loss with this material due to the mold wear and resin costs if you are trying to make a business out of it, so the pressure vessel and compressor is a must-have to do it right.
Drop me an email and I will see if Pam can get some contacts and I can give you some advise.
Thanks,
Tony C.

[Tony Castronovo]

Gordon,
You have come along way with your CAD capability and I am very impressed! You may want to consider a 3-D ABS plastic printer? You can make nice "touchy/ feely" parts and also they would make great patterns for the silicone / resin production molds. There are many on ebay that work really good for under $1000.00. Just a thought, I think you are there and ready for the future of pattern manufacturing.

[Gordon T Haley]

thinking of 1/4 scale V8 as an engine cowl on a drag boat, skiff, cracker box, or  a GN racer or a jet boat like my dad had in the 80's.

[Gordon T Haley]

Tony totally understand about new houses ...don't over do it. I have been watching "smooth-on" videos on YouTube. Not the same as using alginate (like I did in the prop shop many years ago) but close. I have made many plaster and clay molds as well. yes not inexpensive. I checked into getting a 1/4 3D print of a Ford 427, too expensive.My 3D drawings are not "up-to snuff" yet too many holes and not solid.  Thought of using the one and only 1/4 scale engine out there. I don't want to buy a 1/4 scale model worth over $200 to just cut it up to fit over a 26cc engine. Also not a good idea to copying it. But I could use it as a starting point and make it my own. If changed enough it is not a copy. Something that would have same shape, but not look or be made of the same material, or made the same way. But then again if I change it so much, just make a "plug" from scratch. Main point being is I see what's out there and think " that's not scale, it doesn't even look right" 

MMM thinking of a "pressure vessel" "canning" 30 quart pressure cooker/canner :) just don't tell my wife. just kidding but it would work with an addition of a few parts as Tony mentioned earlier. 

[Gordon T Haley]

mmm just looked at wife's pressure cooker. gauge only goes to 15 psi, not sure if it could handle 80 psi. maybe not as good of idea as I thought. 

[Tony Castronovo]

Gordon,

There is a book called, "The Prop Builders Molding & Casting Handbook" See if you can get a copy it is fantastic and goes over most of the molding procedures used in the movie, hobby, and art industries. It has great pictures and goes step-by-step from patterns to making and pouring molds.

Thanks,

Tony C.

[Gordon T Haley]

Tony , I did a search for the book. It looked like one of my old textbooks but it came out 10 years after I graduated from theater school. Looks to be a very useful book. 

My local Princess Auto (Harbour Frieght type store) carries pressure painting tanks lower cost than a pressure cooker.

thanks for all the info and help Tony

Gordon H

[Tony Castronovo]

OK, Once you make the silicone mold(s), you use a high quality casting resin and hardener. You only have a few minutes so everything has to be right. Apply rubber bands around the mold to close it, so carefully cut the molds so they are easy to close and hold their integrity. I used to key my molds in all for corners with large keys ( cone shaped ).

The pressure pot has to be big enough to easily house the mold(s). Connect your compressor and install a hand operated valve ( 180 degree ON/OFF ), and also a pressure gauge is a necessity to the pot. Close the pot and run the pressure up to 60 pounds, this is a good number for most high def molding. Once the pot is at 60 PSI, close the valve to hold the pressure. De-molding was usually about 10-15 minutes. Use a specific silicone spray release agent to prolong mold life. That's the quick 10-minute course, always start with small molds and parts so you don't waste as much material when learning. The book I told you about really is specific to the subject.

I built a V8 1/4 scale engine for thermal forming and it is too scale, but a little small to cover the engines, so you may need to go to a 1/3rd scale to cover your engine, most eyes won't notice the larger size. Mine was a standard 350 Chevy and I made all of the parts out of wood then thermal formed over them. I never converted the wood patterns to production aluminum since we never made product. Pam is cleaning out our showroom today and all of our showcases ( prototypes, # 1's, etc ) are going to be packed and stored but I will post a picture of the engine before she packs it away.  I wonder how many will notice that the heads are not offset? That was because I wanted to make only one mold that was "straight-up" to save time and make it easier.

Thermal forming may be your best bet, and if you make the patterns I will run your parts for you. You would need to give me a call so I can give you good direction on do's and don'ts for thermal forming. You could easlily put two, maybe three complete engines on a 2' X 2' mold base and if made from 0.060" ABS, one sheet pulled would cost about, $25.00. I would think that if you did a good job and made the kit easy to assemble you could sell a few.

Thank,

Tony C.

[Gordon T Haley]

thanks again Tony

That is cool. Did you use heat resistant resin? What does the motor go into?

Gordon

[Tony Castronovo]

No, that is 100% .060" thermal formed plastic from a sheet. We made it for the original Cracker box class in 1992 as a prop to put in our hull for trade shows. It is hollow inside and is put together like a plastic model kit witht he same styrene based cement. It took me about 3-days to make all of the part patterns, the intake pattern was the hardest and was made with Bondo and hand shaped.

Thanks,

Tony