3d Printer Plastics and Silicone Rubber Molds Question

3D Fabrication
1

Hello again,

So I am interested in creating 1/2" scale cement blocks for scale building models. I would like to make the positive mold template for these blocks using a 3d printer, and then use a 2 part silicone rubber mold to make the negative mold form. I was thinking of using a silicone rubber like Smooth On mold star 30.

I was curious if anyone knows what kind of plastic filament would be best being poured over with this type of rubber mold casting and if anyone has had success before trying this out. Any advice is appreciated.

Thanks in advance!

2

I frequently use ABS to go the other way. It works well.

I suspect sealing and smoothing the ABS template with acetone would help for what you want to do. Bear in mind…

  • Acetone is highly flammable.
  • ABS dissolved in acetone instantly adheres to skin
  • ABS dissolved in acetone does not adhere to nitrile gloves
  • When using acetone on ABS, a little bit goes a long way
  • It takes about three days for ABS to fully release acetone
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3

I’ve got a related question I’d like to tack on: anyone know if it’s ok to put printed parts that are partially hollow (20% infill for example) into a vacuum chamber for making silicone molds?

4

Do you use aerosoled Acetone or did you brush it on? Curious, does this deform the finer details?

5

Acetone’s high vapor pressure practically makes it self-aerosolize at room temperature.

A container (like a paint can) with a paper towel lining the inner wall and a small amount of acetone in the bottom (in uniform contact with the bottom edge of the paper towel), should result in a consistent vapor. The paper towel helps the acetone travel upward (via capillary action) and diffuse more uniformly in the chamber.

Place your part in there for a few minutes and it should be smoother.

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6

I’ve done this with ABS and Mold Max 40. I printed a cup mold, then made a silicone mold of the print. I used the silicone molds to make plaster molds. The photo below is silicone and plaster, I didn’t keep the 3d print. I didn’t do any smoothing, but I probably should have just to make sure the silicone didn’t leak to the inside of the print. I was new to 3d printing and mold making at the time and I think the biggest issue I had with making the silicone mold from the print was not printing a watertight object.

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That’s it! That’s exactly what I’m going for. Looks pretty good to me for not sealing and is an order of magnitude better than what I’m doing right now with small wood forms.

What density did you use for the 3d print?

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Like 10% infill I think. Probably want to do a large number of perimeter loops though. I don’t know how it’s typically done, but I hot glued my 3d print to the cottle boards to prevent it from floating out of the silicone.

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9

I do. I’ve not had any noticeable problems.

It’s a great question. I honestly didn’t even think about it. I just assumed 3D printed ABS would be so riddled with holes that there would be no trapped air.

For silicone molds I don’t bother trying to seal / smooth. Straight from the printer into the vacuum chamber. All the little layer lines end up in the silicone part. The last several things I made are rubber feet so the course texture works well.

I’ve done all three (spritzed, rubbed on, vapor chamber). The vapor chamber is generally the better choice. Just be sure to check on the part; too long and it will sag. It’s helpful to include a place to tie a string then dangle the part from the top. Magnets with a metal can work well for positioning the part and soaked paper towels.

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Much appreciated!