Instructables

How to cut wax master out of silicone mold without damaging it?

I am planning to cast jewellery by generally sand casting with wax models, though I would like to make more permanent silicone mold backups if something happens to the original wax master. My plan would be to pour or press silicone onto the wax master and get it out after the silicone has set. The only easy way I know of doing this is to cut a line all around the silicone mold to retrieve the wax master. I know other people seem to do this. I can't see how you could do this though without accidentally scratching the wax master inside?

rickharris1 year ago
As a general comment sand casting isn't usually a good enough finish for jewellery. In comparison to the detail on the product the sand grains are quite large.

Lost wax casting in investment plaster is the more normal approach.
This calls for a wax master that will be melted so to make multi models a silicone mould may be used to form the wax master.

You have to design your model so that is has minimal undercuts. the mould is made then in at least 2 parts so they can be separated and the model removed without marking the wax. (minimal touching up may be required)

lsadwdwadw (author)  rickharris1 year ago
Thanks for the advice. I thought using sand and wax would be most economical as I could reuse both, whereas with investment you have to keep on buying more and more, unless you made a two part mold somehow where you could reuse it. I saw someone else sand casting jewellery, I didn't realize it doesnt leave a good enough finish. I would be using petrobond oil bonded sand which is said to have a good finish. thanks!
It can be done and I have done it with silver many times at school.

The finish even with fine petrobond is still somewhat rough IMO.

If this was such a great idea all jewellery would be cast in sand for cost reasons.

Investment plaster is very fine and mixed with fine ceramic powder to give more strength. You can use ordinary plaster of paris BUT you must follow all safety instructions as per investment casting.

Any moisture will blow the plaster apart. Get the P of P too hot and it will crumble.

If your casting a flatish relief then experiment with blue tack it will withstand pewter casting temperatures - needs good ventilation.

Even real plasticine is just clay bound with oil - it could work for you BUT isn't done commercially.

For Pewter casting we used MDF wood cut on a CNC machine to repeat the patterns. Works fine.

Remembe PRos don't often sand cast - for a reason.

lsadwdwadw (author)  rickharris1 year ago
ok thanks, I appreciate it. I have used plaster of paris before with wax yes, it seemed to work quite well though I was just experimenting with primitive models. I will seriously reconsider using investment then as quality is important.
lsadwdwadw (author)  lsadwdwadw1 year ago
your link goes to the homepage of the knowledgebase by the way, not sure if you know that.
Ah OK It's the way their data bases works - You can search for wax casting though and get some information
lsadwdwadw (author)  rickharris1 year ago
ok thanks will do
IF you used "precision sand casting" - the stuff done with CO2 hardened sand, you CAN get superb finishes. That said, Lost wax is the way to go, as I say at the end of this thread.
Why not use the wax to make the silicone mould, scrap the wax, and resin cast your patterns in the silicone ?
lsadwdwadw (author)  steveastrouk1 year ago
Problem is if something went wrong with making the mold, then I have ruined the wax master.
Yes, but you are MUCH more likely to damage the master by using it as a pattern !

What shape IS the master ?
lsadwdwadw (author)  steveastrouk1 year ago
I'm not sure if I am misunderstanding, but aren't you also suggesting using the master as a pattern? I'm not sure what the point is of resin casting any patterns in the silicone. I am new to casting.
You have made a very nice wax master.
You propose to sand cast it.
Sandcasting is a pretty rough process for a little wax model.
The wax model won't last well.

So you need to make a resin master FROM the wax by making a silicone mould. The wax is sacrificial. Your work will be preserved in the silicone.

Alternatively, 3D scan the wax and get some 3d prints off it.
lsadwdwadw (author)  steveastrouk1 year ago
Ah, I see, yes resin would then hold up better with sandcasting. My plan was to make wax copies in the silicone mold if and when necessary. I wasn't mad about buying more things but it sounds like the resin would be a good investment and so I could use it repeatedly and remelt the wax. My worry was more that if I spent hours on a wax model and then the silicone mould for some reason failed then I would have a useless mould and would scratch up the wax model when cutting it out. thank you for the advice.
lsadwdwadw (author)  lsadwdwadw1 year ago
I also didn't think sandcasting would be rough on wax, have not tried it yet.
THE way to get good results is "lost wax" casting, especially if you can beg borrow or steal a centrifugal casting machine.
lsadwdwadw (author)  steveastrouk1 year ago
alright thanks for the tip. I have experimented with primitive lost wax casting, but thought using sand and wax would be ideal as I can repeatedly use both. I would be using petrobond oil bonded sand.
Its a risk, but by careful preparation of the mould, you should be fine.
PLAN in advance where you will put runners and gates in the silicone, and make them in wax, fused to your model.