Bronze sword - er, dagger.
I finally finished my bronze sword project!
Kind of. You'll have to watch the video to find out.
Copper refining part 2
Last Friday I finally got around to melting down a bunch of old scrap copper that I'd had lying around for months. I've now got enough copper and tin to cast my bronze sword!
My technique has really come on since I built my bucket furnace. I borrowed a friend's leaf blower for the air induction and it's way better than Kat's old hairdryer.
I've discovered that it works much better with real charcoal than charcoal briquettes, which leave a lot of claggy residue in the furnace and stop it getting hot enough.
Here's a quick video showing the refining of the scrap copper into pretty little ingots. It takes about two hours to get hot enough to melt the copper at 1084 °C, but then it's so hot that it melts down the next batch in a couple of minutes.
The molten copper is indescribably beautiful and quite took my breath away. It's a pale shimmery metallic salmon colour with a strong orange glow. I think I'm a little bit in love with it. I watched a Youtube video of a guy pouring gold a while ago, he said that after you see your first pour the metal takes up a little piece of your heart forever. I think I know what he means.
At the end of the video are the wooden model sword that I carved, and a test aluminium version that I cast last year. Can't wait to cast the bronze one!
I've just had my first go at copper refining from some old scrap copper pipe, and it's really really hot.
I've been playing with aluminium up to now which melts at a balmy 660 °C, easily achievable with my furnace. Copper melts at 1084 °C which makes it glow bright yellow!
Here's a quick video of my first attempt at copper.
Metal casting furnace
My aim this year is to cast my own bronze sword, and to do that I need to melt the bronze. I just made a bucket furnace that's good enough to melt copper and tin, the metals in bronze alloy. My furnace is based on the Mini Metal Foundry on Youtube.
Here are ingredients to make it.
- 10 litre metal bucket - the body of the furnace
- 5 litre plastic bucket - to make a void in the centre of the furnace
- 15 litre plastic bucket - to make a lid for the furnace
- Tin can - to make a void in the centre of the lid, to release pressure
- Two metal hoops - these will become handles for the lid
- 1 inch steel pipe - this is the air intake for the furnace
- 25kg dense castable from Castree Kilns
- dog - serves no useful purpose
Making the lid
First of all I made the lid, with 10kg of the dense castable and 1.3 litres of water, mixed thoroughly.
I set the tin can in the centre of the mix and sunk the handles into it. Then I let it cure for 48 hours. The dense castable material is strange stuff, it's very dry and at first I didn't think it was going to cure. But 48 hours later it's hard as rock.
Making the body
I needed to make a hollow body for the furnace, so I used a small bucket filled with water in the centre to make the void.
I used 15kg of dense castable with 1.95 litres of water, which pretty much filled the bucket. I let this cure for 48 hours as well, and spent several hours cleaning all the gack off the kitchen table, floor and ceiling.
The mistake I made here was spilling some of the dense castable into the white bucket in the middle. When I poured the water out, there was a 2cm layer of rock hard material in the bottom - turns out it sets underwater just fine! I hacked it into little pieces and pulled it out with no problems.
Once it had set, I used a hole saw to cut a piece out of the side, and fitted a steel pipe to force air into the furnace. This is hooked up to Kat's hair dryer - shh, don't tell her!
Here's the finished furnace, the next step is to fire it up!
Here are some pics of the first time I lit it up, to melt some aluminium as a test. Aluminium melts at a much lower temperature than bronze, so it's easier to work with and cheaper.
The crucible is made of ceramic bonded clay graphite, it's a Salamander A2 from Castree Kilns. It's rated to 1600°C. The original instructions I followed used an old fire extinguisher, but I've been told that these are quite unreliable and prone to sudden failure.
Finally here's a quick video of the furnace in action:
The next step is to make a sword template out of wood and then cast it.
I've no idea how that works but it's going to be fun finding out!
One of my most ambitious projects is to make a bronze sword, which involves learning a whole bunch of new skills. My original plan was to get tin and copper ores, and smelt them to refine the metals, but after a visit to Geevor tin mine I realised that I'll need at least a tonne of rock, so I'm going to buy tin and copper metal and start from there.
So my first task is to make charcoal to make the bronze.
I didn't really understand what charcoal was until I started researching this project. Essentially it's wood that's been heated in the absence of air, to remove all the water, oils and other volatile chemicals, and leaves pretty much just carbon. The absence of air is the really important thing here, because otherwise it just burns.
Because all the water and stuff has been removed, it burns massively hotter than wood, hot enough to melt tin and copper and make bronze. I only need a small amount to make a sword, so I found a method that you can do in an afternoon, and Rob and I got stuck in.
Here's what we did, and you've got to guess what we did wrong.
A simple kiln
First we acquired a 200 litre drum and a 60 litre drum and cut the tops off with a jigsaw (below, left), which is a legitimate use for that tool. We cut small flaps into the bigger drum to allow air to get in.
Both drums had previously contained engine oil that we didn't want in the final charcoal, so we lit fires in them both.
While they were cooling down, Rob sawed up some dry logs (below, middle) and we packed them into the smaller drum so tightly that we could turn it upside down without them falling out (below, right). This is important.
So far so good.
Cooking the wood
Next we turned the small drum upside down and placed it in the middle of the big drum. Then we packed sawn up pallets all around the edge of the big drum (below, left) and set light to it. We kept feeding the fire and let it burn for two hours (below, middle).
This heats the wood in the smaller barrel in the absence of air, which turns it from wood into charcoal. After two hours we let the fire die out, and let the barrels cool down until we could touch them (below, right).
Then we tipped the large barrel onto its side and carefully pulled out the small barrel, which was now full of charcoal!
The charcoal was still really hot, so we put a lid over the barrel and left it for a few hours to cool down.
Cocking it up
Spotted the mistake yet?
When we came back to check on it three hours later, the charcoal was on fire!
Because we were so excited we removed the small barrel too early and a stray ember from the fire must have landed amongst the charcoal, which was nice and hot and suddenly had access to lots of oxygen.
Oops. But it was obviously good charcoal because it was blisteringly hot.
So we've all learned an important lesson today here folks: you can't hurry love. We'll be making another batch soon, and we'll be much more careful this time. And we salvaged one bag of usable charcoal before it all burned.
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