Tag Archives: cast necklace

How to: Forge metal

A couple of years ago now I taught myself how to do rudimentary metal forging using videos from the internet and the occasional digitised book. Here’s the summary of how to do it if anyone else wants to have a go!

Warning: Learning to forge things in metal is dangerous, you should proceed with caution at all times. In particular you risk setting fire to things (including yourself), burns, self inflicted stab wounds and other nasty things if you aren’t sensible. 

Safety items you should have to try forging: A head mounted welding face mask (you will need both hands). Flameproof overalls (I use Nomex ones, also remember to wear natural fibres underneath just in case). Leather welding gloves. Tongs for manipulating very hot things. A face mask to protect you from projecting molten metal is also a good idea. A leather apron can also be useful as it’s comparatively resistant to molten metal. A bucket of water handy is also a very wise precaution.

Step 1: Decide what you want to forge.

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This weekend I decided to forge a moon pendant, based on the above sketch.

Step 2: Carve it in wax. I used a tea light from IKEA, vanilla scent, however you can also buy proper (harder) carving wax from specialists. If you want high detail, this is a must! You can also buy it in pre-formed ring blanks. Be careful when cutting the wax, I’ve previously cut myself quite badly doing this using an Xacto craft knife, but fortunately it’s healed now!

Step 3: Cast the mould. For this you should find a tin can (aluminium or steel) that’s big enough to hold the wax piece. If you’re only detailing on one side then an open mould is fine, stick something on the top of your model to allow it to be rested on top of the can. Otherwise, for more complicated castings such as rings, you should include a sprue and a cone on the top of the mould to allow you to pour in the liquid metal. To make the mould, I used pure plaster of Paris, however you can/should also add some sand to improve the strength of the mould. It’s a good idea to tap the side of the mould vigorously to ensure that any bubbles on the wax model get dislodged. Ideally you should put the mould under a vacuum to remove all air bubbles, but vacuum pumps are hard to come by. I’ve managed without one so far.

Step 4: Wait for the mould to dry. There’s no shortcut for this.

Step 5: Bake out the mould to melt the wax and ensure that the plaster/plaster+sand mixture is fully cured. You might want to build a mini kiln for this, here’s mine. 20170722_195429

It is constructed from a concrete air brick, sawn in half and then drilled to create a cavity and a connection point for a heat gun. It has a top half which is the same, but with a small vent hole instead of the inlet. Here is a picture of the completed kiln.

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Note the small hole on the top for the hot air to come out of. I placed the cured mould, complete with the wax model, upside down in here for about 30 minutes to bake it and melt out all the wax. You could probably just pour in the molten metal, but baking out seems to be more reliable.

Step 6: Whilst the mould is baking, you can set up your furnace. I used an arc welder, since it’s easy to get hold of and runs on easy to handle electricity rather than anything chemical (coal, propane, etc.). To turn the arc welder into a tool for forging, you should remove both the ground clip and the welding rod holder and replace them with large metal mole grips. These can be used to hold the electrodes and/or a crucible. I would recommend using a graphite crucible and graphite rods extracted from 6V ‘lantern’ batteries – be careful not to crack them while extracting them from the 4 zinc housings within the battery. It’s also worth noting that if you obtain them this way, they will be coated in a paraffin type wax which will burn off after the first time you strike an arc.

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Here is my ‘workbench’ you can see the arc welder is the yellow box at the end, with both electrodes replaced with mole grips. I used a small part of the concrete air-brick as a stand for the crucible, here’s a close up also complete with my cracked crucible which I disposed of after this casting and the mole grips holding carbon rods:

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Step 7: Melt the metal. For this step I can highly recommend using some borax as a flux, you can buy it (normally) from your local chemist. It’s not the nicest of chemicals, even though it was used as washing powder in the 19th century, so use sparingly (a light dusting in the crucible is plenty I find) and handle with care. Next add your metal in small chunks that fit in the crucible. For this project I used some silver elements I had left over from another project. Silver is cheap, at least compared to Gold, and melts a lot easier than Copper. Beware of metals containing Zinc as breathing in the vapour can give you the shakes and fever like symptoms. Copper is VERY HARD to melt, and once molten, re-solidifies almost instantly. I started practising with it and was mightily relived when I switched to casting in Silver.

Step 8: Pour into the mould. You should remove the mould from the kiln and place it next to your crucible workstation before attempting this. Pouring the metal in is surprisingly difficult and you really don’t want molten metal splashing or pouring onto anything else (you, clothes, wood, anything that will melt or burn). Once you’ve melted the metal, be sure to lift your welding visor otherwise the mould will be invisible (along with anything else that isn’t an electrical arc or glowing metal).

Step 9: Apply the plunger (carefully!). If you look carefully at the photo of my workbench you’ll see a broken stick of wood attached to the lid of a jam-jar. This is my plunger for steam casting. When you have poured the metal into the mould, you can push the plunger down on top to generate steam and force the metal into unoccupied parts of the mould. You should prime the plunger by stuffing it with newspaper and then wetting it (in your safety bucket of water). However, if you are casting in an open mould, there’s limited benefit to the above, as assuming you used a sensible amount of flux, and it’s hot enough, the metal will naturally fill the mould. In this case, I was overzealous and plunged the plunger down onto my filled mould whilst the Silver was still liquid, creating the following mess:

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You can see the blobs of molten silver that were pushed out by the steam, and the blackened lump in the centre is what I pulled out of the mould itself, which was also looking rather worse for wear. It’s worth noting that metals, generally, can be purified and re-cast even when they look rather messy. The impurities will either burn off or sink to the bottom of the crucible.

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The mould, after use. This type of mould is only intended for a single use. However since I was in a hurry (never cast in a hurry!), I decided to re-use it and modify my original design somewhat. I placed the lumps of silver into the mould and created an arc between the two electrodes in close proximity to the mould (1-2mm max), in order to re-melt the silver into the mould. This worked very well, though changed the nature of the end product.

Step 10: Quench and finish. After re-melting, I was careful to wait for the casting to cool before dropping the whole mould in my handy nearby bucket of water. After a few seconds bubbling, I retrieved the cast using a pair of pliers and tidied it up using a grinding wheel and a wire brush polishing wheel. Since the mould had been abused during the two pours of the casting process, there were some fragments of gypsum (plaster) embedded in the surface of the final cast. These soon came out under the polishing wheel whilst I was improving the overall shape and look of the piece. 20170722_195339

Here is the front of the finished pendant, with a very lunar surface look to it. There’s a 2.4 mm hole drilled into the top for the silver chain, at a slight angle to help it sit ‘moon side up’ when worn as a necklace. I didn’t cast/make the chain, as that’s far too much like hard work, instead buying it from a local jeweller.

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I polished the back side of the pendant to a much smoother finish, with the idea that it would be more comfortable to wear. During the polishing process it got so hot that two tool marks imprinted into the Silver, you can see them towards the bottom. I decided to leave them as they look rather like footprints to me!

Casting is a lot of fun, however it can be extremely hazardous so should only be done with extreme care. It took me about 3 months of occasional evening and weekend practice before I was able to make my first ‘proper’ cast, and I’m still a very, very long way from even a student level of proficiency. But it kind of works, and I’m very happy with the end result. I’m also not going to give up my day job!

P.S. I must give credit to The King of Random for his excellent Arc Furnace video which was my inspiration for using the arc welder to melt metal!

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