Best filament for going to RTV rubber molding

I have designed some parts that I will be 3D printing on my TAZ 5. Since the final parts will need to be able to stand up to being baked in an oven at 130C for 30-90 minutes, I am planning to cast the parts in polystone. My three main concerns are smoothing the 3D print before molding, making sure the print is sufficiently solid to stand up to the weight/pressure of the RTV rubber during pouring and set-up, and making sure that there are no chemical conflicts between the filament and the RTV rubber.

I have on-hand:

  • Esun HIPS
  • Esun PLA
  • Village Plastics ABS
  • colorFabb nGen
  • taulman 3D n-vent
  • I’m not opposed to picking up a different filament if need be.

I know that there is a method for smoothing ABS with acetone or with XTC-3D. I haven’t really seen anything about smoothing the other filament types other than sanding.

I know that the item to be molded should not have sulfur in it, because this causes problems when trying to mold items made out of some commonly available types of clay.

I have checked with the manufacturer of the molding material I am using, the polystone casting material I am using, and the clay I will be sculpting over the final object (hence the need to stand up to oven baking). None of them have any experience at all using their products in conjunction with 3D printing.

All that being said, any input on the three issues I know I may have? Any input on any issues I may not know I have?

Thank you in advance.

Vapor smoothing ABS and HIPS with acetone, or PLA with MEK (not as smooth as ABS with acetone), is an easy way of making your finish smooth. Sanding and XTC-3D works well too, but is more labor intensive (XTC-3D is pretty nasty stuff I think).

In terms of strength, I would rank those materials, from strongest to weakest: n-vent, ABS, nGen, PLA, HIPS. I am not familiar with RTV rubber molding so I’m not sure how much strength you’ll need.

The problem with ABS, and n-vent to a lesser extent, is that both materials warp somewhat bad. How big of parts are you printing? I would recommend you print you part with ABS, and if it doesn’t warp too much (sanding the bed with 1000-2000 grit sand paper helps!) and is of acceptable quality, vapor smooth it with acetone. I’d recommend a cold vapor smooth since it is safer and harder to “over-smooth” because it is a slower process.

If it is a large part and warping too much, I would recommend PLA and sanding/vapor smoothing with MEK. If this turns out to be too weak, a few filament makers make stronger versions of PLA: Polymaker, taulman, esun–I have tested them all and they are all much tougher than regular PLA.

If everything you try is just too weak for the molding process, I would recommend this polycarbonate by Polymaker: It’s the strongest filament I have ever printed with (and I’ve printed with a LOT), and it doesn’t warp nearly as much as other polycarbonates. It can be annealed, too, for additional strength.

If you’re looking for high temp filament that can handle high temperatures for and extended period, I’d suggest ColorFabb HT or Makergeek High-Temp PLA. Both make very strong prints and can withstand very high temps.

Thank you for your replies. I apologize for not posting sooner.

Thank you for the feedback on XTC-3D. I was going to order some, and it’s good to have the warning. I will have to look into the acetone and MEK processes some more, both hot and cold. I haven’t had any problems with ABS sticking to the bed (actually just the opposite) unless the contact area is extremely small, and using Brim seems to take care of that.

The parts are not particularly large. Basically, I am making my own 3:1 LEGO minifigures for sculpting accessory ideas in clay like in this official LEGO video:

Thank you for the suggestions. Mold making is new to me, but I have already purchased some materials, so I’m going to try molding the 3D parts in RTV and then casting in polystone first. If that doesn’t work, I’ll try the filaments you’ve suggested. I really like what I’ve seen from ColorFabb on the clear (HT or XT?) so I may have to give some of their higher end filaments a go whether this works or not.

Maybe it’s just me, but I just threw out 3 spools of Makergeeks High Temperature PLA.

No matter what temperature I print it at or how much or little pressure I put on the Idler, it gets chewed up in the Hobbed Bolt. It comes out fine for the first 1/2 to 1 inch of height, then gets chewed up.

I got tired of spending so much time trying to get it work that I just gave up on it.

Have had zero problems with Proto-Pasta High Temerature Ice and Smoke. The Coffee is OK, but seems to ooz a bit more.