Question on Mold material and resin casting

rocketrider · Post by **rocketrider** » Sat Aug 05, 2006 11:28 pm

I have read through a lot of the threads here on casting your own models, and im overwhelmed with the info.

What throws me is pressure casting or degassing, I know what it is, but I dont have the equipment or the money to get it.

What mold material can I get that does not require anything but mix and pour. Also what type of resin would I use to create the actual model?

I have laid out plans for a simple spaceship (about 12") that I would like to try to cast and possibly sell.

I know of Smooth On, Reynolds & artmolds, but again, im unsure of which products to purchase.

Provided links would be cool

Thanks again in advance

Glen

Umi_Ryuzuki · Post by **Umi_Ryuzuki** » Sun Aug 06, 2006 1:30 am

Any of the mold materials out there can just be mixed an poured.

If you are not pressurecasting, you don't need to de air the RTV.

However you have to be more meticulus when pouring the mold because you can trap air bubbles around detail parts, and under cuts on your master.

It is best to pour a thin layer over the master part, and let it settle. While it is settling, I usually would put a first layer on a second mold I had prepared. As the RTV settles, work out air bubbles against the master part with a tooth pick or similar object. then add more RTV.
By working back and forth on two small molds you can be sure the parts have a good coat of RTV and then you can fill the mold by pouring a thin stream into one corner.

After the mold is full, I used to spend about 15-30 minutes jiggling them and popping air bubbles...

Glad I don't have to work that way anymore.

Sparky · Post by **Sparky** » Thu Aug 24, 2006 2:08 pm

Don't forget the 'bombs away method' of de-airing the RTV. they make a good point about bubbles and mixing.

Tap plastics
http://www.tapplastics.com/info/video.php
You want part 2 of how to make a silcon mold, of coarse part 1 is usefull to watch too.

Antenociti · Post by **Antenociti** » Thu Aug 24, 2006 4:18 pm

hehe - excellent video, not heard it called "bombs away" before

REL · Post by **REL** » Thu Aug 24, 2006 4:27 pm

Brush on the first coat of silicone and let it half way set up, then pour on the other coats until the mold is as thick as you want, and pour the rubber from about 2 feet high making a thin stream.

For resin use a slower setting mixture like Smoothcast 310 from Smoothon. It takes over an hour to set up and demolds in 4 hours. It's almost water thin so it get's into all the tiny cracks and crevices, and since it sets so slow it has plenty of time for the bubbles to rise and pop. Always be sure to baby powder and spray mold release on the molds. I use Mann Technologies Ease release 200, spray it on and let it dry for about 15 minutes before pouring the resin, the mold release will force the bubbles away from the surface of the mold.

I've never had to pressure cast or degass anything using these techniques.

Sparky · Post by **Sparky** » Thu Aug 24, 2006 11:01 pm

I tried the brush on with oomoo 30 and it didnâ€™t' work for me. This was on the defense towers, the little I beam ends that had been glued on as well as the turbo shaft cylinder from the top of the PL bridge still had bubbles in them. These were very small gribblies with a lot of little folds/grooves, and the oomoo's mixed viscosity is very high.

http://www.kc6sye.com/images/images_02_ ... rdiges.jpg

I was not able to make copeis of these which I had wanted to do before we drilled out the holes seen in them above. I molded them twice and used the brush on method for the second try. After that I got started looking for vacuum systems, which I use now.

REL · Post by **REL** » Thu Aug 24, 2006 11:15 pm

Try the Moldmax 30 and put a super thin brush on coat, almost transparent and let that set up, then brush on a second coat. After that you can pour it on and it should be just fine. I've molded super tiny detailed parts with lots of undercuts that way without one single bubble.

http://sovereignreplicas.com/SM/

Edit: Something else I had to do, I got the 1/2" brushes then cut half the bristles off making them a lot stiffer so I could brush the thick silicone down into the detailed area's.

Sparky · Post by **Sparky** » Thu Aug 24, 2006 11:23 pm

I use the mold max 30 now, and I have a vacu pump. The best of both worlds, moldmax is easy to use, I was measuring it out with a ktichen scale to start with.

REL · Post by **REL** » Thu Aug 24, 2006 11:28 pm

I tried the venturi pump and didn't have much luck with it, I don't think it ever got enough of a vacuum to do anything. If I ever have to make a large mold where I'll pour the silicone in to fill a void between a master and mothermold I'll have to invest in a nice vacuum pump.