TEBerg
Posts: 99
Joined: 1/20/2004
From: Clovis,
CA, USA
Status: offline
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Dave, Thanks for the words of support.. Been a long time since I was in the CG, but still try to keep in touch with some friends.. I'm just a geologist working for the California EPA right now..
Ram-Bro,
I don't know if I have enough pics to do a tutorial on casting parts.. I did a lot of searching on the web before I even tried it..
What I have found out so far (besides the fact that my "paintable" release agent leaves fish-eye spots in the paint - sanding and re-painting today  ) is the following about casting plastic..
- I liked using the 1 to 1 Silicon Rubber mix for the mold. I did not want to purchase a small scale accurate enough to measure what I needed by weight (usually 10 to 1), so I went with the blue/green 1 to 1 that you can measure by volume for the correct mix.
- The easiest molds were where I could fasten a basic part on to glass and use a tin can or plastic bottle for the mold. You just super glue a flat side of the object down and then hot glue the mold sides to the glass. Pour in the mold mix and let it set for the correct time, which is about 4 hours for the 1 to 1 mix. The mold will pop right off the glass with the master piece and you can easily release it from the sides with some alcohol (rubbing, not drinking)..
- 2-part molds are easier to use, but much harder to make.. I tried to make a base under the master parts with modelers clay for the two prop parts. It is very dificult and took more time to try and build up a 1/2-inch thick base than I cared for.. I actually lost some of the twist I had built into my master propeller blade because of 'flexing' it when I worked the putty around and tried to seal it at the edges.
- I used a "medium" hardness plastic for the parts.. I have see on-line that Alumilite seems to have the highest numbers for the shear strenght and heat resistance. Micro mark also makes a "heavy duty" pourable plastic. The compounds I bought came from AeroMarine Products through John's E-bay store. The statistics were a bit lower than Alumilite and the thin propeller blades seem to be a bit flexable. Kinda like how the older white Top Flite blades used to feel.. But, John's prices were much better than the other 'name brand' mold products.
- I have "over mixed" more plastic than I care to think about [)].. You can measure the empty mold with rice and go with that volume, but I ended up short on a couple of casts. That also left little pieces of rice stuck on the silicone mold that ended up in the next parts.. The best way to estimate plastic volume was to submirge the master part in a measuring cup of water and read the difference in volume..
- If you need air vents or blank areas in a mold, USE SMOOTH Fillers such as tooth picks, bamboo scewers or straws. For example, we needed screw holes in my sons climbing grips, we just poked holes through the green styrofoam master with a drill and figured they would be good screw holes.. Well, we should have used straws, because the rough screw holes continue to grab the mold rubber and break the rubber off inside the cast piece.. We now just have nubs where the screws go and have to drill out the screw holes. But - That works great also[)]
I like the following links the best for information about casting parts: http://www.micromark.com/html_pages/instructions/82708mrrresinart.pdf, http://www.info-central.org/construction_moldmaking.shtml , http://www.alumilite.com/HowTos.cfm.
I hope it is OK, to include those links..
What I really learned from the casting is that: unmixed silicon mold compound will stain your workbench The plastic compound Will come off a painted garage floor, if you work very hard and are careful scraping it up YOU NEED MORE Silicone Rubber and Plastic than you think you will need... And, My son had a blast carving his own climbing grips and casting them in plastic..
I ready to make up a "master" for the M117 bombs I want to drop along with the toilet.. I'm going to try using the Alumilite 610 Foam for those.. Their Tech support said the foam was very durable and should make great RC bombs.. But, I'm already out of the 1-quart kit of 1 to 1 silicone rubber.. I had purchased 1/2-gallon of the plastic and I have used about 1/3 of that.. So, if this propeller project works and I can sell a couple of the extras I made, then I can afford to buy more mold mix and get some casts done for the bombs..
This was probably not a lot of good instruction, but please feel free to contact me with any questions about what I have done so far and how it worked..
Edited to Add: I went ahead and put up a "tutorial" for making molds and casting some plastic and foam parts in the "Tips and Techniques" Forum.. You can find the thread here: http://www.rcuniverse.com/forum/m_7432180/tm.htm
It includes the scale M117 bombs and bomb clips..
Blue Skies,
Tom
< Message edited by TEBerg -- 4/29/2008 7:36:23 PM >
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Blue Skies,
Tom B.
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All Forums >> RC Airplanes >> RC Warbirds and Warplanes >> Global Skyraider Build 
Global Skyraider Build - 
.. 
... NOT EVEN Close 
.. Once I have a good looking prop completed, I'll be able to sell them and I can describe how to obtain a good looking finish.. 
