Lost Wax Casting

[Nick martin]

Good afternoon everyone,

Some designs that creep into my head that need casting, would only be suitable for lost wax casting given their complexity and shape.

I dont have a vulcaniser or a centrifugal casting machine, and I know its an expensive setup to purchase. I know you can send the wax masters off to a casting company but I prefer the idea of doing it at home in my small workshop for lots of reasons.

So is there anything stopping me from creating the wax model, pouring in the investment plaster mix, using a kiln to burn out the wax then using my regular blowtorch setup to melt the metal and cast it instead of relying on a centrifugal setup?

Basically I'm looking for something more flexible that delft-clay, and with which I can cast complex models. Something like silicone rubber is ideal because it retains and reproduces fine detail, but of course you cant cast molten metal into it. Are there any alternatives that I've not noticed?

Cheers,

Nick

[Dennis]

Well Nick, It is possible to pour into investment, contained in a casting ring, provided you have it glowing and prepare it as you would a cuttle fish mould: that is with a thick sprue and several vents.

However the piece would have to be fairly simple with no very thin parts and the chances of failure would be quite high. Centrifugal casting machines are not very expensive and there are probably used ones around.

The one below involves the dreaded Ebay, which you don't like and you would still need to contain the machine in a cut down metal dustbin, or some such dedicated contraption, to avoid the risk of scatter. Dennis.

http://www.ebay.co.uk/bhp/casting-machine

[josef1]

Nick If you can maybe go for the combined Vacuum unit, you will need a vacuum to pull the air out of the investment anyway so you may as well cast with it aswell, you can use your torch to cast and Ive seen second hand units on eBay for reasonable money. this is an example of a Chinese machine so not sure of the quality but this sort of set up gives good results and is pretty simple to use .http://www.ebay.co.uk/itm/Jewelry-Lost-Wax-Cast-Combination-Vacuum-Investing-Casting-Investment-Machine-UK-/221810590411?hash=item33a4f102cb. It seems expensive but I suppose its worth it when you have spent ages making wax models just to have them miss cast. Also look out for this book http://www.amazon.co.uk/Centrifugal-Jewelry-Casting-Tradesmen-Craftsmen/dp/0910280053 it old but its awesome if you want to get into casting you will only need a vulcaniser if you want to make reproductions of your models so you can make rubber moulds and inject them with wax

[ps_bond]

My recent reading has thrown another suggestion on the vulcaniser - using bolted plates and heating the whole assembly in an oven instead.
Or there's RTV, but the consumables costs are quite high; I think I might switch to using an low-temperature silicone instead.

[Dennis]

What Joseph says is quite true, but at entry level you don't need vacuum investing either.
When I were a lad, they just used a wetting agent and vibrated the investment in-not even with a vibrating table, but just the wooden centre of a polishing brush, notched and run on a polishing lathe to provide the vibrations. Dennis.

[Nick martin]

Thanks Josef, those machines on Ebay dont cost a fortune but I dont grasp quite how they work fully. I'll do a better search to see if theres a video clip of them in operation, but cheers for the link. May well look into one of them.
Have however ordered the book off Amazon on your suggestion, thanks for the pointers.

Nick

[Nick martin]

Hello Dennis,

Those centrifugal machines arent expensive at all, quite surprised actually as ones I'd looked at some time ago cost upwards of £1000!

I'm not neccessarily wishing to make multiple wax's, or to produce moulds to inject wax into. Its more a case of wishing to cast models that aren't 2D in shape, have undercuts in them, or have fine detailing that needs reproduced.

If for example I made a wax model of a ring design that had intricate design carved along the shank, then this wouldnt be reproduced well using cuttlefish or delft-clay. Dont get me wrong, I enjoy using these two methods and with cuttlefish I achieve great results although it usually involves a lot of hand refining and cleaning up. Not that I mind, but its time consuming.

Going to do a lot more reading on the subject as its never a bad idea, and I like to know everything inside-out before purchasing equipment.

At the moment I'm thinking on an entry-level basis as I've never tried lost wax casting before. If I had a vulcaniser ( or using a vibration technique ) and a kiln, then I'm hoping that I could at least produce the lost-wax mold then possibly cast into it using my regular crucible technique or invest in a centrifugal device.

Peter: Does RTV refer to silicone rubber moulds?

Thanks everyone,

Nick



Well Nick, It is possible to pour into investment, contained in a casting ring, provided you have it glowing and prepare it as you would a cuttle fish mould: that is with a thick sprue and several vents.

However the piece would have to be fairly simple with no very thin parts and the chances of failure would be quite high. Centrifugal casting machines are not very expensive and there are probably used ones around.

The one below involves the dreaded Ebay, which you don't like and you would still need to contain the machine in a cut down metal dustbin, or some such dedicated contraption, to avoid the risk of scatter. Dennis.

http://www.ebay.co.uk/bhp/casting-machine

[ps_bond]

RTV is Room Temperature Vulcanising - it's a 2 part rubber solution that sets to a solid rubber. As with investment it ought to be vacuumed, but there are workarounds in the Castaldo data sheet that seem to work OK. The Castaldo RTV (which they're at pains to point out is not a silicone rubber) is expensive stuff, messy to work with and the moulds have a life of 1-2 years before they degrade but the initial outlay on kit is lower than going over to vulcanised.

If you're carving waxes then I wouldn't worry about the moulding side so much (until after you trash one you've spent ages on...).

As with all casting, any intricate design will probably need cleaning up with a graver or scorper post-casting.

[Nick martin]

Thanks Peter,

If I recall correctly, I think Andrew Berry did some video demonstrations / tutorials on RTV moulds now I think of it? Will have to have a look again to see if I'm correct. Thanks for clarifying that, and yes casting does require lots of cleaning up as you say. The other route of course is hand engraving rings as opposed to carving the wax and casting them, but unfortunately my engraving skills are nowhere near good enough yet!

Nick


RTV is Room Temperature Vulcanising - it's a 2 part rubber solution that sets to a solid rubber. As with investment it ought to be vacuumed, but there are workarounds in the Castaldo data sheet that seem to work OK. The Castaldo RTV (which they're at pains to point out is not a silicone rubber) is expensive stuff, messy to work with and the moulds have a life of 1-2 years before they degrade but the initial outlay on kit is lower than going over to vulcanised.

If you're carving waxes then I wouldn't worry about the moulding side so much (until after you trash one you've spent ages on...).

As with all casting, any intricate design will probably need cleaning up with a graver or scorper post-casting.

[ps_bond]

He is, there's been a few sessions on Periscope in that vein; he's using the clear (even more expensive) version; it's a nice touch, but I'm not convinced the benefits outweigh the increased cost.
It turns out I rather enjoy the visualisation aspect of mould cutting.

[Dennis]

I can't believe that what I wrote in the middle of the night is not here today. I must have omitted to save it. Anyhow, here is the gist:

When I were a boy and vacuum investing had not become available, they used a wetting agent on the wax and vibrated the casting ring as the investment went in.

They did not even have vibrating tables, but cut a criss cross into the wooden centre of an old polishing brush. This mounted on the lathe, provided the vibration.

Dennis.

[ps_bond]

That's strange - I can see that as post #5?

[Dennis]

That's strange - I can see that as post #5?

Yes, you're right Peter. you are welcome to delete the duplicate if you wish. Dennis.