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"Casting in plastic" Topic

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1,230 hits since 7 Dec 2022
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Mark J Wilson Supporting Member of TMP07 Dec 2022 3:40 a.m. PST

Anyone out there done this. I've given it a go using Prince August molds, which yield good quality figures, but the plastic I'm using [Smooth Cast 300] takes about 2 hours to cure despite being billed as fast setting, so progress is slow. Anyone who can say "I use X and it takes 30 minutes to cure" will be my friend for life.

Eumelus Supporting Member of TMP07 Dec 2022 8:36 a.m. PST

I'm intrigued! I've long wanted to give the PA molds a try, but was put off by the mess and costs of metal molding. Do the figures come out well (sabres, gun barrels, bayonets fully formed)? What release agent, if any, do you use? Does the Smooth Cast plastic hold paint well?

TheOtherOneFromTableScape07 Dec 2022 10:22 a.m. PST

Smooth-on products are usually very reliable. You have to get the mix ratios correct, mix properly and do it at a suitable room tempaerature. If it is cold it will cure much more slowly. If you are mixing small quantities it is almost impossible to get an adaquate ratio of A to B by volume. Get some gram scales and do it by weight. I find it easier to poor in the thinner component first, and then add the thicker one second. Measure and mix in the same container, so that you don't upset the ratio by leaving residue in the measuring container.

Finally measure and mix a test sample. Just leave it in the mixing container watch it cure. It should begin to go opaque and then white in a couple of minutes. Once you have mixed it should get warm. The more you mix the hotter it will get and the quicker it will harden once it has gone white.

I hope that helps.

Personal logo Sgt Slag Supporting Member of TMP07 Dec 2022 12:02 p.m. PST

I have heard of, and watched a video on how to mold miniatures using Hot Glue injected into molds. They came out better than I imagined they would! I do not know about small portions, like sword blades.

Here is a search result listing for Hot Glue molding. Several videos of possible interest. I really like the one where he makes a 28mm figure, with wire armatures, allowing it to be posed.

The first video, at the top, recommended using vegetable oil as a mold release agent. I would recommend trying a liquid silicone lubricant, brushed onto the mold halves.

I would also recommend using a High Temperature Hot Glue, for making molds, and a Low Temperature Hot Glue for making castings:
the High Temperature Glue won't melt as easily as the Low Teperature Glue, which will be added to the mold, to make the castings. If you use an RTV Silicone mold, I would recommend using High Temperature Glue, to hopefully achieve better detail, as it will remain molten, and less viscous, longer. Pressure is also necessary to force it into a closed mold cavity, and I remember seeing a video where the maker used his Gun to inject molten Hot Glue into a closed mold. Watch the video, search for more, as they will likely have more useful information than what I can remember.

Hot Glue, once solidified, will take craft paints nicely. I know, I've sculpted a few Treants (wire armature), and multiple rock and ice stalagmite terrain pieces (crushed toilet paper tubing armature), covered in layers of Hot Glue. Once painted, you cannot tell it is Hot Glue. The sculpting depends entirely upon your abilities, or a mold, if used. Cheers!

d88mm194007 Dec 2022 2:22 p.m. PST

Try Alumilite. My buddy and I have been using it for decades.
The link should take you to the easiest one to use. And the less expensive.
All of their products are great, from the RTV rubber (room temperature vulcanization) to the resin.
I love making plastic rocks from those rubber molds from Woodland Scenics. They are lighter and more durable than plaster of Paris.

Bunkermeister Supporting Member of TMP07 Dec 2022 7:03 p.m. PST

If your Smooth Cast 300 is taking 2 hours to cure you are doing something wrong or got a bad batch. 20 minutes at 70 degrees or more for me. I have used it for decades. Either you are not measuring it right or you are not mixing it properly or your resin is very old.

I use little plastic medical cups to make very small amounts, less than 30cc and it dries fine. You have to mix it until it is uniform in color with no swirls.

Call Smooth-On if that does not help. Their customer service is great.

Mike Bunkermeister Creek

bentbent07 Dec 2022 8:09 p.m. PST

I've seen a great hot glue casting of Frodo, left unpainted for obvious reasons. Useful for when Frodo tried to slip away unseen.

Mark J Wilson Supporting Member of TMP08 Dec 2022 2:24 a.m. PST

@ Eumelus
The quality is good, the strength is acceptable to me so far; I'm pretty sure it will be no worse than you get from 28mm plastics. The release agent is Ease Release 205. I have to admit that to date it's not been the easiest surface to paint. Due to ill health I got some figures made but then stalled on the painting; a spray on undercoat may be key.

Mark J Wilson Supporting Member of TMP08 Dec 2022 2:27 a.m. PST

Smoothcast are of the opinion that I'm doing things correctly and it's the small size of the molds, which means they don't get hot enough to cure more quickly. I've also found that longer time means more robust when it comes to musket barrels which are obviously the weakest past of infantry castings.

Mark J Wilson Supporting Member of TMP08 Dec 2022 2:35 a.m. PST

@ d88mm1940

Thanks for this but it's about 2.5x the price and when I get going I'm looking to do enough figures to make this prohibitive.

John Leahy Sponsoring Member of TMP08 Dec 2022 12:35 p.m. PST

I used CR 600 casting resin from Micro Mark. I also used their molding material. The resin sets up in 30 to 60 minutes. Closer to 30 if it's 28mm sized. I have used it for years. Good stuff.



Mark J Wilson Supporting Member of TMP09 Dec 2022 4:12 a.m. PST

@ John Leahy

Thanks for this one, which looks cheaper than the Smoothcast. Two follow ups, how do they paint up and what do you use as a releasing agent.

John Leahy Sponsoring Member of TMP09 Dec 2022 8:07 p.m. PST

Hi they carry a spray release agent. The resin turns a white color. Easy to prime and paint. I use Lego bricks as my moldbox. I can send you links to some YouTube videos created years ago that show the process. The big deal is how to create the vents for the molds. I use plastic needle-less syringes to inject the resin into the molds. The vents allow the resin to flow into the mold. You tap it several times to eliminate air bubbles. The videos are a huge help. There are 5 or 6 of them. They are good at walking you thru it. I've molded for metal castings starting in the 70s with homemade and Prince August molds. Then it was resin figs. Now I 3d print.

Thanks John

Mark J Wilson Supporting Member of TMP02 Feb 2023 11:27 a.m. PST

Sadly it appears I can only buy CR 600 in the US and shipping is prohibitive. Anyone know of a UK equivalent.

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