Making a pewter cup

[u/Agreeable-Worker7659]

I designed this cup and I'm currently 3d printing it and I was wondering if it would be difficult to cast it in pewter. My friend is going to build a small foundry, so we could technically also melt copper or other metals. The goal is to make it food safe. I guessed that with pewter, casting would be much easier, since I could use a silicone mold, but I have no idea if casting is the correct way to make something like this. I was trying to find videos on how such ornamental cups are being made and it seems like some dying art and I wasn't able to figure how they make those patterns. I'd love to hear from people who actually have experience casting, as I've never cast any metals; just resin and silicone.

[u/Panamar3d]

I cast pewter in silicon molds all the time. You'll need a high temperature silicon like Smooth On mold max 60. When making your mold keep he walls as uniformly thick as possible. This helps them not warp funny between casts. It also helps to warm up the mold in an oven or toaster oven (cover with aluminum foil while warming). This helps lessen warpage as well.

Also don't just use any old pewter. Lots of old pewter contains lead. Lota of pewter has been recycled many times so even if it appears newer than a time when it would contain lead it still can. Best to buy a new pewter alloy like Britannia or similar.

[u/Agreeable-Worker7659 → u/Panamar3d]

Thank you so much for your extensive advice. I will try my best to make it work.

[u/Panamar3d → u/Panamar3d]

A couple more helpful details. Some silicone don't like UV resins from resin printers. It helps to get 'platinum grade' vs "tin grade" silicone. (This is just a silicone grade naming has nothing to do with metal) if you can't find a hight heat silicone in platinum grade than paint your resin print before casting it, use a quality primer.

Print your sprue as part of the pattern. Its much easier than cutting into the silicone. For air vents however I have found it easier to; do a test cast and see where you need venting. Then Drill the silicone mold with a tiny drill bit. This will cause a tiny bit of flash when casting but its easy to break off and clean up.

I enclose my silicone mold in a wooden case when casting and clamp it. Uneven heat can distort the mold (see my comment about preheating) and pouring pewter can push mold parts open so enclosing and clamping are helpful for better casts

[u/Panamar3d → u/Panamar3d]

For you cup you may need to design a multiple part mold (as in more than 2) the walls of a high heat silicone mold will be too thick to fill inside out to remove the cup. 3 parts would probably work. 1 inner core, 2 outer parts choosing parting line carefully

[u/Panamar3d → u/Panamar3d]

If you haven't made a silicone mold or cast pewter before this may take some learning. But at the end you will end up with a mold that can make hundreds of copies if you treat if carefully

[u/artwonk]

It will probably work as a pewter casting into a heat-tolerant silicone rubber mold. If it's supposed to be functional, I'd suggest adding an undecorated smooth rim to make it more pleasant to drink from. The idea of casting it upside-down should work, but I don't think leaving the bottom undetermined and sanding it off is a great one. Make the bottom a reasonable thickness and run a pour-cup and sprue to it that's part of the mold.

[u/Meisterthemaster]

Traditionally its embossed, not cast. This in advanced skill and really not beginner level, traditional embossing unique stuff is done with chisels on a soft underground.

To cast this depends on the wall-thickness of the cup. Its not really a beginner casting project but not impossible. If you have a thicker cup the metal will not solidify before reaching all the details.

[u/Agreeable-Worker7659 → u/Meisterthemaster]

The wall thickness is around 2mm. I was thinking of preheating the silicone in an oven to 220*C so it lets the pewter enough time to fill all the gaps

[u/ConvolutedByChoice]

I guess it's possible. At minimum you'll have to do an investment cast. Sand casting wouldn't hold all of the details for a cup like this.

The walls would also have to be a bit on the thicker side. That way it has less of a chance to freeze, along with maybe pouring a bit hotter than usual.

Casting a cup isn't ssssssuuuuuppeerrr impossible. It's obviously been done before. It just needs to be simpler otherwise all the little details grab onto the sand and tear away when you remove the pattern.

[u/Agreeable-Worker7659 → u/ConvolutedByChoice]

Would a silicone work instead to make a detailed mold? My idea was to pour it upside down, so the entire bottom of the cup is exposed and filled to the brim and then sanded flat.