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Post by vsotto on Oct 25, 2018 20:56:06 GMT -5
Greetings. I successfully created my first mold using the Mini Casting kit. After watching and reading countless videos and articles I was pleasantly surprised how well the mold turned out. It was a simple mold to learn how the process worked. My mold is a one-piece shallow plate with some shallow undercuts. I mostly wanted to test how the product worked. It
the piece is about 1" square textured styrene which is about 1/16" thick. The undercut is
approximately 1/16" around the edge.
However, I had less than successful results when pouring the first casting. The casting picked up the surface details incredibly well. However, their were voids at each of the four corners.
Can anyone point to some common situations that would cause this or how to remedy it. Keep in mind, I'm just a beginner.
I have since read on other forums to apply baby powder prior to pouring the resin. I may have missed that step, but will try it tomorrow morning to see if results are better.
One concern I have is the viscosity of the resin while I was pouring it. It seemed to be thicker than the videos of other RC-3 resin I've seen on youtube. It's seemed to be the consistency of thin syrup, while the resin in the videos seemed to flow like milk. Additionally, the resin began to cure closer to the 6-8 minute mark after being mixed and was still soft and flexible at 25 mins.
I purchased the kit at a box store, so who is to say how long it may have sat on the shelf. What is the shelf life for an unopened container? Is there any markings on the bottle to know how old it is? I looked, but did not find anything.
Thanks, and looking forward to more experimenting.
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Post by Brian on Oct 26, 2018 6:57:39 GMT -5
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Post by notoes on Oct 26, 2018 12:39:02 GMT -5
Congrats on your first mold and castings. There is just a couple things I'd like to add to Brian's answer - the age of the mold itself. Most molds need to hit full cure to do a good casting consistently. The full cure time for most is 7 days unless you do some "post curing" which is putting some heat to the mold to speed up the cure. For my small molds, I usually make sure that I zap them in the microwave once or twice (1 minute on high and let it cool down in between) before trying a casting. Also you can warm the RC-3 up a bit before mixing by putting one or both sides in warm tap water (be sure the caps are on tight and the bottles don't tip over!) for a couple minutes then once they are the consistency you like, measure and mix.
I believe the shelf life is 6-12 months unopened and I think it's 6 months after opening though I've seen where some have had really old resin work with no problem. It mostly depends more on how it was stored (temperature-wise) than on how long it sat there. Also you might can fix those corners with "drips" from the next pour if they don't need any details. I've been known to take a couple drops leftover from the next pour to fix holes from the previous pour.
Try the above tips and let us know how it works for you.
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Post by Brian on Oct 26, 2018 23:12:07 GMT -5
......Now that I have a little bit more time , I can delve into this a little deeper....
If this mold is one that you intend to keep, you will need to use a mold release. A mold release will prolong the life of your mold and helps to "release" your casted resin part from the mold.....Alumilite sells Stoner Mold Release, I use Price-Driscoll...either way both are fine products.
When applying the baby powder, use a brush...I use a cheap, small paint brush...like what you would use with a model car....brush into every crevis/undercut. Gently blow off any excess. The powder has no adverse effects on the resin as far as appearance or texture.
To help work the resin into the undercuts, gently squeeze the mold while you pour. This also forces any air bubbles to the surface.
The smaller the mold, the more accurate you have to be with your ratios where resin is concerned.....while there is some tolerance with the RTV Silicone rubber , there is virtually none with the resin. In the first link I posted, I stated the minimal amount of resin that can be poured. If I can quote myself " I think one the biggest issue people are having is the mix ratios by being off. The closer that I can get to an absolute equal amount of both parts "A" and "B" the better results that I had. MIX NO LESS THAN 1/2 oz. OR 14.1748 GRAMS OF BOTH PART "A" AND "B"...THATS NO LESS THAN 1/2 oz. OR 14.1748 GRAMS IN THE PART "A" CUP AND NO LESS THAN 1/2 oz. OR 14.1748 IN THE PART"B" CUP. 1/2 oz. or 14 grams..thats it , no less." What I do is pour a few molds at once so that I don't have to be concerned with the minimal amounts.....If I'm pouring small parts, I'll mix up 1 oz. of "A" and 1 oz. of "B". Use of a digital scale is a must....being off as much as 1 Gram when mixing for a smaller mold can be enough to ruin the resin and make it unusable. It sounds like, from your own description, that you were off a little bit with your mix ratio as far as cure times, still soft and flexible after 25 mins. etc, etc.
I think I hold the world record for the oldest RC-3 still in use.....I have a gallon set that's going on 4 years old as close as I can figure....I just keep them stowed under the work table in the hobby room. Because of the age of the RC-3 that I am using, after pouring into the cups, I stir the parts "A" and especially "B" before combining the two.....I usually stir anywhere from 30 seconds to 1 minute...both should have a consistent look through out.
There is no way to determine how old a kit is... there are no codes or dates that I am aware of. I am literally in the middle of dispelling any discourse out there about HS-3 that is purchased from a big box store being bad or going bad soon after purchase....I purchased some 3 months ago, used some of it to create a mold a couple of months ago alumilite.freeforums.net/thread/475/25-scale-dry-sump-mold ......will use more than likely the rest after the new year when it will have been 6 months since it was purchased. I have purposely done everything that your probably not supposed to do..i.e leaving caps off for extended periods of time, no special provisions for storage.....just where ever in the hobby room...direct sunlight..etc. I had absolutely no issues what so ever with creating the mold 2 months ago and I feel very confident that I will have no issues with it in three months. All I did was to fallow the simple instructions and used the digital scale. I will post the outcome and results early in 2019.
Don't be afraid to experiment....I've learned a lot by doing just that.
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Post by vsotto on Oct 27, 2018 8:35:15 GMT -5
Thank you for the advice and encouragement. The most recent castings were more successful, but still had a few problems.
Things I did differently.
1) Warmed the molds in the microwave for a minute or two.
Q) Should I pour the resin while the molds are still or warm or wait until the cool
2) Brushed baby powder on the molds.
3) Used more resin. Previously I was mixing only a few milliliter as that was all the mold required. But it now makes sense that being off a half mill from 5 mills has much more significant difference than being off a half mill from 15 mills.
Next I will try to
1) warm the resin a bit before mixing it.
2) I ordered a gram scale and will use that next to measure. Previously I was measuring by volume using the cups that came in kit.
3) Should I try to cut/drill holes in the corners for excess resin and air to escape? I realize that I will need to clean up excess from further castings.
I attached a couple pictures, because who doesn't like looking a photos. The masters are on the left and show progression to the right. The master on the second row is upside-down to show the undercut.
By the way, I've been really impressed how easily and nicely the round items and those with no sharp 90-degree corners have come out. I will definitely continue to experiment. These have just been experiments to figure out how this product works so I don't make mistakes on real (larger) projects.
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Post by notoes on Oct 28, 2018 17:50:26 GMT -5
Not bad for experiments, you're coming right along with learning this well.
1) Yes when you warm the mold, the resin goes in while it is still warm. I usually time my mixing to be done a couple seconds after the microwave is done heating the mold. The heat from the mold will help the resin cure faster so be aware of that but it also is helpful in that way for small parts.
2) The baby powder is something that is recommended but I've never really used it, half the time I don't even use Vaseline unless it's where I don't want two silicone parts to stick to each other (such as in a two part mold).
3) Yes, it's always better to mix up more than one mold worth if you're working with small molds. I try to do at least two or three whenever I can on my small ones. I even pull out molds that I'm not going to use the casting right away so that I can mix a good sized amount of resin. When you mix a small amount, it does have an impact on how they cure.
On your next list:
1) Remember to make sure the caps are on tight and that they stay upright. It won't take long (or rather it shouldn't) so a minute or two might be all you need.
2) I use them too but mainly for just holding the resin while I use my scale.
3) With those molds, I don't really see that you need to. Tapping them or the surface under them should also help any bubbles to raise up and out. Just be sure to be quick about your mixing and pouring - 30 seconds should be all that's needed to fully mix them and you should have until the 2 1/2 minute mark before it's too far cured to do anything. If you don't have something to time it, you should get something. I wear a really old school calculator watch (yup I'm old...) with a stopwatch feature that I use every time. Since it's on my wrist, it's easy to keep track of the time - plus if I happen to get something on it from the gloves, it's not a big problem.
And one other thing, those castings aren't a waste - you can "recycle" messed up/un-useful castings in bigger castings. I use castings that don't come out nicely as filler in new castings. Course I have to cut them to pieces with line pliers but it works for me. If I didn't do it this way, I'd have wasted about two or three sets of resin (32oz bottles).
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Post by vsotto on Jan 2, 2019 19:02:55 GMT -5
I wanted to circle back and thank everyone for the suggestions. I have had much more success in the past two months. I created a couple of different molds and found the softer rubber makes a huge difference in the final products. I have found I really like the High Strength 3 variety.
I have found applying baby powder really helps the resin seep into the corners. I also now mix a minimum of 30ml of resin when pouring a casting and just pour the extra into another mold.
I am no longer concerned that the resin does not cure with 10 minutes. In fact, my expectations are now that it will not set for at least 7-10 minutes and I leave it in to mold at least an hour, usually two. This isn't a problem for me.
I am really enjoying this process.
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Post by notoes on Jan 4, 2019 9:43:36 GMT -5
That's good to hear! I cast in small molds and usually leave mine for close to 20 minutes or longer to get a good hard cast before demolding. Opening the mold (if you can) sometimes helps to get into corners too.
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