All URLs

URL: Glazy Plaster Calculator

Click the link below to go to this page

Related Information

Pouring the v4 plaster beer bottle mold

This picture has its own page with more detail, click here to see it.

This project is a testament to my wife's patience with me using her kitchen as a mold making shop. Most of the tools I need are there. A nice stable table to run two 3D printers, lots of room and plugins, electrical appliances, utensils and supplies of every type, good lighting. And pleasant company!

I have already poured PMC-746 rubber into 3D printed block molds and have printed and put in place stabilizers to hold the rubber in place. Embeds are in place on both the bottle base and bottom mold (upper right). The flexibility of this rubber is amazing, it makes possible extraction of the plaster base, although with difficulty. It also preserves the embossed logo on the foot. This is version 4 (version 5 will have a shallow base piece and modified sliding natches).

The $5 garage sale mixer does not pull bubbles to the surface so I just pull them up by counter-stirring with a serving spoon. A common sense workflow (never pouring any down the sink, cleaning everything in a settling bucket) makes this no problem in the kitchen.

The 3D model of a new melt flow tester mold

This picture has its own page with more detail, click here to see it.

The two pieces print as shown (top left). Since the walls are thin they may bulge a little when plaster is poured in, this is a trade-off for their light weight. The back section prints with no support, the front one needs support turned on. The file is in 3MF format, this enables including all pieces in one file (STL format does not permit that). All modern slicers can handle 3MF and they enable individually placing and orienting each piece (it is best to print them separately).

Plaster: Do not to forget to insert the clips and embeds into the holes before pouring the plaster. The mold volume is 1750cc. According to the https://plaster.glazy.org calculator, 1370g water and 1960g potters plaster are needed. You may like to mix 300:210g of plaster:water first (in a large paper cup) and pour that into the bottoms, this assures no leaking or deformation during the main pour.

Finish: Use a heat gun to peel off the PLA shell. Dry the mold and flatten the matting faces on sandpaper if needed. Then, insert the natches and spacers into the embeds. Strap the halves together, insert the pouring spout and pour in the casting slip (use a slip intended for the temperature you fire at).

Mixing and pouring plaster into a 3D printed shell mold

-Size of mixing container needed: 1L per 1000g of plaster.
-To determine the amount of plaster and water needed our normal process is to counterbalance the mold and fill it with water to get the cc volume, in this case 2000. Then use the glazy.org plaster calculator for the amounts of plaster and water needed. But this time I just used the gram/weight as the amount of plaster, 2000g. I derived the water, 1400g, according to the 70/100 ratio recommended by USG (it was 200g less plaster and was sufficient).
-Using a 4-minute soak and a good propeller mixer there is no need to sprinkle the plaster in.
-Make sure no plaster is hanging on sides of the mixing container after soak.
-Mix with a whirlpool shallow enough that it does not suck air but deep enough that it is pulling bubbles up to the surface.
-Make sure the mold is strong enough not to split at the bottom and is a strong shape that will not bow out. 3D print it so the artifacts are at the top. For PLA mold soap is not normally needed.
-Make sure the mold is sitting on a very flat surface.
-We had to apply tape to the bottom flat surface to make sure it is watertight.
-Pour the plaster into the mold in a steady stream that does not pull in bubbles.
-Remove using a heat gun when the plaster is set.

Links

Got a Question?

Buy me a coffee and we can talk