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Resin Casting Question


VonL
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I've been experimenting with Alumilite resin casting materials and got decent results with their RTV mold-making stuff. Problem area is that the 50/50 resin mix starts setting up after about one minute in the pot, which is about how long it takes to mix it properly. It then has little time, and too much viscosity to flow out into the far crevices of the mold, much less any time to coax out bubbles. There is an old reference to a Micro-Mark brand resin on this board. Is that stuff better?

 

Suggestions?

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I've been experimenting with Alumilite resin casting materials and got decent results with their RTV mold-making stuff. Problem area is that the 50/50 resin mix starts setting up after about one minute in the pot, which is about how long it takes to mix it properly. It then has little time, and too much viscosity to flow out into the far crevices of the mold, much less any time to coax out bubbles. There is an old reference to a Micro-Mark brand resin on this board. Is that stuff better?

 

Suggestions?

 

Ditch the Alumilite and go with Smooth-On 305. It will give you at least a 7 minute working time. Their Mold Max 30 RTV is also excellent.

 

http://www.smooth-on.com/Urethane-Plastic-...1209/index.html

 

http://www.smooth-on.com/index.php?cPath=1135

 

I haven't head anything good about Micro Mark's stuff. Everyone I know uses Smooth-On. Burman Industries also makes great stuff; used it about 10 years ago but switched to Smooth on because they were less expensive, on my coast and sold small "Trial" sizes of their resin and silicone. Perfect for me as I don't do a lot of casting and unused resin will crystallize in about 6 month.

Edited by TheMadKlingon
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I use the white alumilite stuff. Slower cure and very runny. I only get bubbles occasionally. I still use Micro-Marks rubber.....for me the 50/50 mix means no math on my end.

 

 

Tom,

what is the runniest of the resins they sell.....I need some stuff so I my switch.

Edited by Mark Aldrich
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Hi Bob,

- FWIW, I've used the Alumilite RTV sets quite a bit to cast copies of my original masters and copies of other (out-or-business) guys stuff. The beauty of the Alumilite stuff is that Hobby-Lobby carries it and if you get one of their 40% coupons off of their website, its a great bargin. And to add to that, Hobby-Lobby carries Alumilite's Heavy duty RTV sets too. This RTV works great with highly detailed parts like ejection seats.

- As for their casting resin.....toss it! The work time is atrocious.

- For casting, I have been using Micro Mark. They have a CR-300 and a CR-600. Obviously, they are both two part resins. The 300 has an approximate 3 minute pot life with a 15 minute de-mold time and the 600 has an approximate 7 minute pot life with a 30 minute de-mold time. Either set runs $32.95 plus S&H for a total of 32 oz. I prefer the 600 so that I can poke a prob into the mold and get all the air-bubbles out before it "kicks" and have had great success with it. The down side to these resins, (and I suspect it is true for all resins) is that it seems to turn bad (crystallize) way too soon, if you don't use it within a few months. I can sometimes stretch their self life after opening them, by squeezing the bottles (to get the air out) just enough and tightening the caps as the fluid reaches the top of the bottle.

- I've known about the Smooth-on stuff for a few years, I just haven't gottin around to trying it yet. Maybe during the Xmas holidays, I can give it a shot. HTH and Model on, Brothers of the Liquid Sprue. :smiley14:

Edited by Weedeater
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THANK YOU for this intell, guys! Looks like I need to order up a set of the Mico-Mark '600, just for laughs.

 

Another odd question about this stuff: I have a small mold for a fairly simple part that gave me a couple of good results and then a couple not so good, as I tried to beat the curing time of the Alumilite resin. One or two parts came out of this mold not completely cured. Can always make a new mold from the master, but will there be any harm in putting some of the new wine into that old wineskin? That is: Would there be residual crud in the mold, preventing the better resin from forming properly at its surface? If so, should one or two tries clean it out, or do I just abandon the mold?

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I've been experimenting with Alumilite resin casting materials and got decent results with their RTV mold-making stuff. Problem area is that the 50/50 resin mix starts setting up after about one minute in the pot, which is about how long it takes to mix it properly. It then has little time, and too much viscosity to flow out into the far crevices of the mold, much less any time to coax out bubbles. There is an old reference to a Micro-Mark brand resin on this board. Is that stuff better?

 

Suggestions?

 

Here at Flagship Models I prefer the Mold Max-30 RTV Rubber. For casting I use Smooth-Cast 321. It allows enough time to mix and de-gas in very small parts.

 

What exactly are you trying to make a mold for?

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What exactly are you trying to make a mold for?

 

Various small bits for airplanes right now. The master discussed above is an ECM blister for the 1/72 Monogram B-1B. Planes are the comfort zone, but this is my learning curve for trying lots of different stuff in the future.

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Various small bits for airplanes right now. The master discussed above is an ECM blister for the 1/72 Monogram B-1B. Planes are the comfort zone, but this is my learning curve for trying lots of different stuff in the future.

 

I was only asking out of curiosity. If you keep having problems, send me the part and I'll make you a mold and cast you few parts.

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  • 2 weeks later...
THANK YOU for this intell, guys! Looks like I need to order up a set of the Mico-Mark '600, just for laughs.

 

Another odd question about this stuff: I have a small mold for a fairly simple part that gave me a couple of good results and then a couple not so good, as I tried to beat the curing time of the Alumilite resin. One or two parts came out of this mold not completely cured. Can always make a new mold from the master, but will there be any harm in putting some of the new wine into that old wineskin? That is: Would there be residual crud in the mold, preventing the better resin from forming properly at its surface? If so, should one or two tries clean it out, or do I just abandon the mold?

 

 

I had that happen once, the resin was old and just never cured. I was told to try using some MEK and that worked. It made the residual resin cure, it was of no value as a part, but it cured enough to get it out of the mold.

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  • 2 weeks later...

Silicon rubber (RTV) molds are not impervious to the chemicals in casting resin. Eventually, the rubber mold will degrade, harden (lose it's flexibility) and some fine details may tear loose when removing resin parts. It could also alter the curing characteristics of the resin you're using. How many good castings you get will depend on which brands of RTV and casting resin you use.

 

When I feel a mold is no longer giving me the crisp details I want, I cut the RTV into 1/8 inch cubes. Then I mix a small amount of new RTV to coat the master about 1/8 inch thick. When that cures, I mix another batch of RTV and dump in some of the cubes to form a slurry that fills the rest of the mold. RTV bonds to itself (which is why mold release agents are necessary), so I get a new mold surface backed up by the re-cycled RTV cubes. Haven't had any problems with this approach in years.

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