The Casting Call: Smooth-Cast 300


Last week I played around with MoldRite 25 to make a mold for a part I needed. Fun stuff. Of course, making molds is kinda silly if they don't get used. So, this week I got to actually casting some parts. I could have cast them in epoxy (thought about it), but that would be costly, time consuming and overkill. A quick setting plastic would be more ideal. Enter Smooth-On Smooth-Cast 300. It's a two part system for casting hard urethane plastic. It’s easily paintable and sets up hard in about 15 minutes. It also doesn't require a scale (nice).

Using the material is rather easy. You mix it 50/50 by volume and then it’s a race. The 300 series "locks up" in 2-3 minutes (called the "pot" time). That is just enough time to mix it and pour it, assuming you’re organized.

Just combine, mix, and pour. But don't dally!

I might also mention that the material is not forgiving. It doesn't warn you that "it's getting there", it just moves from a clear pourable liquid to an opaque white solid in less than 20 seconds. On the other hand, if successful, 20 minutes after pouring you can demold your part and actually use it!

Elapsed time: ~20 seconds. I told you not to dally!

The results you get may not be as good as using degassed epoxy, but then again, you don't have to wait 24 hours or have a special vacuum system either. The final product is sandable and non-toxic (after it's totally cured in a day or so), and takes filler, glue and paint well. And my little part? Well, I'm happy. A few holes drilled and some filler and paint and I'm good to go. I only need to cast 5 more.

A finished part and a little 55 gallon hazwaste drum to check the detail level.

Some precautions are in order. While setting up, this material gets hot. Smooth-on says up to 212 degrees F and I believe them. Wear gloves and if the mixing container gets too hot - just put it down. I have never had the 200+ degree experience, but if you mess up the mix ratios just a bit or try to play with the mold while it's setting, it can happen. Just set it down and come back in 20 minutes and try again. The material is cheap, a $20 dollar kit will make close to a liter of material - more than enough for me to cast half a dozen of my little fan ducts. No reason to burn yourself trying to save material. I have never seen (or smelled) vapor coming off the setting plastic, but with the heat it generates you want to be aware that it could happen and use a moderatle ventilated area.

Detail with both the Smooth-Cast and MoldRite can be very good. It appears MoldRite 25 can reproduce ~50 micron detail - and the Smooth-Cast reproduces it as well. So when the MoldRite makers said, "Forensic grade," they weren't kiddin'. That said, I did have trouble with air bubbles in the MoldRite mold it appears. Part was my fault for not being patient. Part is the fault if the MoldRite for being so thick it's barely pourable. The Smooth-on product didn't give me near as many problems with air - so it's a keeper. You can get kits at most fine art supply stores or online.

Ducted fan mock up - time to get a drill!

Happy Moddin'

Our bit of bling comes from modder Bill Owen as he praises…um… 3M Tape - lol - It really is good tape.

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