Dog’s Head: Plaster Mould


Making the plaster cast of the to-be-lost wax copy of the dog’s head: This whole process is a bit tedious, to be honest. I am starting to wonder if there isn’t some easier way, using the 3d print as the “lost-wax-copy” and skipping all these stages. Anyway.

Process

Steps 6-9 on Wikipedia Lost-wax casting page.

Spruing

I had 4 ‘out-sprues’, for gas to escape, and one funnel to pour metal into. Photo below. Attaching these was easy enough, you just heat the end of the sprue and hold it on where you want, but you end up with something quite delicate. I do not do delicate too well.

The wax-copy-to-be-lost. In funnel on the right, out-sprues on the left.

Plaster Mould

Prep 1 – Container

Find a suitable container for plaster mould. I really wanted to find a steel tin, a paint pot would have been good, then I could have just left the plaster cast in the tin and it would have worked as containment steel. I ended up lining a plastic tub with wire fence mesh to reinforce. The mesh lowers the risk of the mould cracking from the molten-metal heat.

What I poured plaster into.

Prep 2 – Plaster of Paris

I  made up my plaster with 1-part plaster of Paris, 1-part water. I also added some silica sand and a grated up refractory brick. I read this would make the plaster cope a little better with the heat.

Pour in Plaster: Massive fails #1 and #2

  1. I did not mix up enough plaster to fill the damned mould. I had to frantically mix up two more batches.
  2. My delicate out-sprues broke off mid-pour. I had to blindly sink them into the wet plaster till they hit the wax cast. So, no idea where they ended up, and definitely not where they were supposed to be.

Burn Out

I left it overnight in the kitchen oven at ~220C. This seems to melt out all the wax okay and seemed to dry the plaster okay. Also lined the oven with a layer of wax 🙁

Testing – Check sprues.

I poked around into each sprue hole one with wire until I got into the main cavity of the mould, then blasted blowtorch into the funnel. Flames came out of each sprue hole so I guess I got lucky with my emergency-fix sprues (though in totally wrong places). I thought the blow-torch blast would also burn off any residual wax.

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