I'm trying to get back into my modeling. Haven't really mastered 3D printing yet, so looking at molding and casting pieces-parts that I need. Used to do it with the resin from Smooth-On, and they're certainly still available, but an unholy great lot of the How-To videos on youtube use clear epoxy resin. I did a search here on the fora, but found only one reference to the stuff, and that wasn't about casting the parts.
Is epoxy resin okay for casting mainly fine-definition parts? Should I stick with smooth-on or it's ilk? (Yes, I'm trolling for information. )
Long answer: it depends on what you are casting. If it's small, open-faced jewelry type things in clear, then yes, epoxy will be fine. Just follow the YouTube tutorials and you will have to go in layers.
If you are casting two-part molds or thicker than say 3/8 of an inch, you need to go with the polyurethane. Do you remember the old Anigrand or Warp kits from the '90s? Do you remember how brittle, smelly, and horribly noxious to sand they were? That technology hasn't really progressed to the point where it's equal in quality and workability as the polyurethane. I'm sure somebody will get on here to disagree with me, but this has been my full-time job for the last 18 years, I hope I know what I'm talking about. Good luck!
Laughter is the best medicine, unless you have diarrhea...
Paint does not adhere well to epoxy. Not the 2-part casting epoxies. Epoxy is used more as a mechanical adhesive. Yeah, you can cast parts out of it and you can even tint or pigment the resin, but don't anticipate spectacular colors. You have to be careful how much pigment you use, too much and it will screw with the epoxy. Urethane resins are probably a better material to cast out of. They clean up and paint well. You do have to contend with bubbles on your surfaces when casting. You can get around that, there are lots more casting resins to choose from than there was years ago. You can get longer pot lifes out of them, but you still have maybe 5-10 minutes. You can cast multiple pours to make hollow parts and to reduce surface bubbes.
I'm pretty much out of the loop. but "casting resin" to me is polyester resin, the really stinky and brittle stuff Warp used and and that I built some 1970s summer camp kayaks out of. Epoxy seems to be a step up from that material- significantly less stink and somewhat tougher. The modern smooth-on polyurethane resins are great to work with- I was able to get use-able parts on my first try with no stink and minimal drama. That stuff works! A pressure pot and a vacuum pump definitely helped, and did not cost much if you are handy and have some hobby funds.
I would never use polyester resin to cast with. It shrinks way too much. If you overdo the catalyst in will get too hot while curing (really shrink) and you can cause it to crack the casting if it is a large volume pour. It can put out a lot of heat when casting heavy, large volume castings. Polyester resins are also much harder on RTV silicone molds (depending on the life span you want from it) it's also very toxic and of course *stinks* profusely. It's not great for breathing or handling. I.M.O, it is only good for fiber glassing and I'm not even sure I'd want to do that using it. Personally, I would never use it. I'd look for an alternative. Epoxies re better in many ways, but they are also very toxic to be in contact with and handle. They shrink significantly less than polyesters, don't stink (but do have a mildly funky odor), but as mentioned are super toxic. You want to be gloved up to your elbows handling that stuff if you are fiber glassing at least. The downside is painting epoxy surfaces. Paint doesn't not take to epoxy surfaces well, but I wonder if there are other additives or coatings you can apply to it that might make painting much easier? Most can be pigmented to a certain degree, but...epoxy is a very dark amber color like pancake or maple syrup, so...I feel like pigmenting it is kind of useless unless you are going for black? For most fiber glassing a polyester shell is usually sprayed in, or you can slush mold it, maybe lay in a very fine finishing cloth and then fiberglass the rest with epoxy and glass fabrics. I think if it's a hollow piece you want, the best thing to do is to do a slush mold, get a thin resin cast going using urethane. I personally think urethane is superior to polyester. It also has a very low shrink rate to it. The problem is the *pot life* if you are working on something complicated by yourself. You can do consecutive pours to build up a desirable thickness before you start glassing with epoxy. Epoxy is by far a stronger resin to fiber glass with and there are dozens and dozens of different kinds made for multiple industrial applications. That's, 'just me'
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