Casting delicate forms

I want to produce some cast pieces from some objects I have, they are basically like cogs or gears, but some are very decorative. Some of the larger ones are very delicate in places with spokes possibly about 1mm wide, maybe slightly less. These particular ones are about 40 mm in total diameter so the delicate spokes are quite long.

I was thinking firstly about mould making and using PMC, but I have found problems with removing them from the moulds, if I let the pieces dry completely they are brittle and prone to breakage, and if I try to remove them when the clay is still wet, it's nearly imppossible not to irrepairably deform the moulded piece. I had some success with a less decilate cog/gear but I think I have messed up the firing or something as when it came out of the kiln it was quite brittle, and now it's in bits! :(|

Anyway, these issues started me thinking about Delft Clay, but this has given me a couple of questions to answer as someone who's never used it before.

I'm concerned about a suitable area on which to position the sprue - I can probably get away with this though as there is a less delicate part on most of the cogs. My main concern however is will the silver flow into all of what will be very delicate and narrow channels in the mould. It will need to go through these and out into the far less delicate frame, so a lot of silver will have to pass through them.

One thought I had was to maybe have two sprues, and therefore 2 points to introduce the silver, but then I guess there would be issues with silver poured through the 1st hole setting before the 2nd hole is poured?

Any thoughts or ideas on this would be appreciated!

I can't help in terms of DIY casting, but if you do get really stuck - I had a ring cast by Weston Beamor in Bham, and it too had a very narrow section between the shank and the stone setting. They were concerned that the neck would restrict the amount of metal that could flow through to the two end prongs of the setting (obviously also very small narrow parts).

They said they could make the neck wider on the mould so that the metal would flow properly, so we agreed they would do this. When I got the finished shank though, I could see that they hadn't done that, and it had worked fine in the end.

I know these things are always nicer achieved by oneself, but from your description and seeing other work WB has done, I would expect they could do it fairly easily - check out this piece on their FAQs page.

I'm no expert, but Delft clay works quite nicely. And if you don't succeed the first time, then you can have another go - that is the beauty of it as a home casting system.

As was suggested, making the sprue bigger, always helps, and extending air holes in more than one place in the mould helps to allow the silver to flow further into the tiny places. You could also trace out a groove from the ends of some of the spokes, and put a couple of air holes extending to the outside from the heavier parts of the piece.

Be interesting to see if it works.

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Originally Posted by pauljoels

I can't help in terms of DIY casting, but if you do get really stuck - I had a ring cast by Weston Beamor in Bham, and it too had a very narrow section between the shank and the stone setting. They were concerned that the neck would restrict the amount of metal that could flow through to the two end prongs of the setting (obviously also very small narrow parts).

They said they could make the neck wider on the mould so that the metal would flow properly, so we agreed they would do this. When I got the finished shank though, I could see that they hadn't done that, and it had worked fine in the end.

I know these things are always nicer achieved by oneself, but from your description and seeing other work WB has done, I would expect they could do it fairly easily - check out this piece on their FAQs page.

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Thanks Paul, that does sound like a good solution, although would essentially result in me having not made any part of the piece! I think though for me it's not a viable solution, as I tend to produce a design and then repeat on request, or make to order if you like.

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Originally Posted by Lindyloo

I'm no expert, but Delft clay works quite nicely. And if you don't succeed the first time, then you can have another go - that is the beauty of it as a home casting system.

As was suggested, making the sprue bigger, always helps, and extending air holes in more than one place in the mould helps to allow the silver to flow further into the tiny places. You could also trace out a groove from the ends of some of the spokes, and put a couple of air holes extending to the outside from the heavier parts of the piece.

Be interesting to see if it works.

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Yes I figured I if I give it a go, I have at worst then got the kit for Delft casting and nothing to cast, but I'd make use of it in the future. Once I have moved and got my new work room set up (which will be at least a month I think :(), I think I will try it out. I also realised if I was careful I could carve a bit more width on the fine spokes out of the clay. Definitley worth a shot!

Thanks for making me realise it just might work!

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Originally Posted by agent_44

Thanks Paul, that does sound like a good solution, although would essentially result in me having not made any part of the piece! I think though for me it's not a viable solution, as I tend to produce a design and then repeat on request, or make to order if you like.

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I understand your position, and having just looked up a few videos on youtube for delft clay I am impressed with how simple it is and am interested to have a go to now.

I assume you cannot do undercuts with the delft?

On using the casting company - it would still take your skill to make the master to be moulded from (unless that is an existing object), but it is also worth noting should you ever need it, that I am pretty sure WB keep the mould for you so you can call on them to repeat it for you. So whilst you may only need one now, you can have more done in the future - and they send the master back to you as well. I realise it is probably also a more expensive option, but it seemed reasonable to me.

I didn't mean to sound dismissive about your idea Paul, so sorry if I did! Definitely something I would bear in minid for the future, but not something that would be suitable for my needs right now.

I'm not really sure what an under cut is, but I know that delft is for one off castings, you need to remould the object you are casting each time. For my needs though this is not a problem.

Don't worry I'm not offended in the slightest. Just a suggestion in case the Delft etc doesnt work. Good luck!

for delicate peices now some casting machines now use vacuum and positive pressure to make sure the item is fully formed. I would advise this because with other forms of casting like delft etc you are relying on the weight of the metal to form the item where as a vacuum would take the air out so theres no bubbles or pressure to stop the flow of metal and the positive pressure would push the metal for every detail!

Hello!:~:

I've never done casting before, but understand that the sprue should be positioned at the thickest point of your casting. This is because if you use a thinner part, then this will soldify more quickly preventing the rest of the casting from filling. Therefore, if you position the sprue at the thickest part, the well of molten metal will take longer to solidify and therefore will flow to the thinner parts. Hope this makes sense!

Looking forward to getting some delft clay soon to have a play!:~::Y:

Hi Polly welcome to the forum:~: