If you want a cool gift for a friend who’s into Math, want to be the coolest nerd in the negihbourhood or just want to try metalworking, this is a great project for you. I always wanted to try casting and the Pi/e contest was the perfect opportunity. I decided to make a bottle opener from aluminum.

Step 1: The Furnace

Aluminum has a pretty low melting point (660 °C or 1220 °F), so it's not too hard to melt it. We can do it even with a homemade furnace.There are several methods for making one at home. The one I used is the easiest in my opinion. The idea came from Grant Thompson. (You can check out his youtube channel here: https://www.youtube.com/channel/UC1zZE_kJ8rQHgLTVf...

For this method you are going to need:

a steel bucket (The size is depending on how big furnace you want to make. The volume of mine was 15 litres or 4 gallons)
a plastic bucket to make the inner space (I used a 5 litre or 1.3 gallon bucket)
a plastic bucket for measuring the components (not necessary)
plaster
sand
water

The inner wall of the furnace is going to be a mixture of sand and plaster with 50-50% and water. You can calculate how much plaster and sand you need if you subtract the volume of the plastic bucket from the volume of the steel bucket. In my case: 15-5=10, so I need 5 litres of sand and 5 litres of plaster.

You only have to pour the material into your steel bucket, then add about 30% water by volume and mix everything. After that place the plastic bucket into the mixture and hold it down for 3-5 minutes. If you put sand into the bucket it helps a lot. Before the plaster fully cures, after about 20 minutes, we need to remove the bucket and cut a hole to the side of the steel bucket for ventilation.

Step 2: The Lid

It's important to make a lid, that you can place onto the furnace, because it retains the heat and lets us melt the aluminum much more quickly. To make a simple lid, pour the same sand-plaster refractory mix into a round tray and place a plastic cup in the middle and place two u-bolts in the mix. Thease are going to function as handles.

Step 3: The Air Blower

The charcoal burns faster and produces more heat if it gets more air, that's why it's important to have an air blower, which is going to be attached to the hole on the side of the furnace.

A hair dryer can be modified for this task. If you open it up, you can see a coil made from hot wire and a small electric motor. We only need the motor. If a variable voltage transformer is soldered to the motor, the speed of the motor can be controlled and it's very useful. When you take the lid off the furnace to remove the dross or take the crucible out, you can turn the speed down. You also start the fire with low speed.

After you are done with soldering you can put everything back together and add a steel barrel to the end of the hair dryer.

Step 4: The Greensand

You can buy commercial greensand, but if you make it at home it works just the same.

The greensand consists of 90% fine sand and 10% clay. I bought the fine sand in a pet shop as aquarium sand. The cheapest way to get clay powder is to buy kitty litter, put it into a plastic bag and hammer it for a few minutes. I doesn't have to be perfectly fine, you can separate the powder by sifting the litter.

Mix thease components together in a big plastic bucket. The sand needs to be wet to be able to hold it's shape. The best way to make it wet is spraying water onto it, then mixing it together, then spraying again and repeating the process until the greensand is OK. Don't try to pour water on it, it's not going to work. To check if it's OK, grab some sand, squeeze it, then try to break it. If it breaks clearly and holds its shape, then it's ready for making the mold.

Step 5: Preparing the Mold

We are using lost-foam casting. The styrofoam burns when it contacts with the hot molten alumium, but the sand doesn't. When you pour the aluminum onto the styrofoam it flows into its place and picks up its shape.

Styrofoam is really cheap, it is used for insulating houses, so you can buy it in builder stores. The 1 cm (0.4 inch) thick sheets are perfect for us. First of all, you need to make a pattern. To make it open Microsoft Word, add pi symbol, change the letter size to 650, chage the font to Times New Roman and print it twice. The surface of styrofoam isn't prefectly smooth, but if we put paper pattern to each side, we can solve this problem. It's a good idea to glue one of the patterns onto the styrofoam sheet with school glue, cut it out, sand it and afterwards glue the other pattern to the other side.

You can buy foam cutters, but if you have a soldering iron you can use that to cut the styrofoam, like I did. If you can change the heat of the soldering iron, chage it to low. If you can't, then turn it off when it gets too hot. You can use sandpaper to finish the pi. You are going to need a a small piece of styrofoam, that you put between the legs of the pi to create a channel for the molten aluminum to flow in. If that piece is the right size, the friction holds it in place.

Choose a cooking pan, which is a bit bigger than your pi. Sprinkle some sand on the bottom then place the pi inside. Sprinkle more sand until only the top of the channel piece is out. Use your hand or a spoon to apply pressure onto the sand to thicken it.

It helps the pouring a lot if there's a feeder over the channel (last two pictures) that holds the molten aluminum until it flows into the mold. To make it, put a cylinder (mine was made out of a steel can) over the channel and fill it with sand, shaping a funnel.

Step 6: It's Time to Cast

Before you start casting make sure, you have every necessary safety equipment:

heat resistant gloves
face shield
heat resistant boots
plers (to grab the crucible)
spoon (to remove the dross)

Now you have everything for casting except the crucible, the charcoal and the source of aluminum, which is usually aluminum cans. For the crucible you need to find a steel coffee pot or a boiling pot. On one of the pictures, you can see a spray-paint can without the top. Despite the fact that the can was made out of steel, it didn't survive the first casting, because its wall was too thin.

To start the casting put the crucible inside the furnace and surround it with charcoal. The easiest way to fire the furnace is using some liquid fire starter. Put the lid onto the furnace and turn on the air blower at low speed (I switched the transformer of my air blower to 3V). Throw the pressed aluminum can into the crucible and wait until it starts melting. Before pouring the aluminum into the mold, don't forget to remove the dross with a spoon. The waste aluminum can be cast into ingots using a steel muffin pan. 10 minutes after the pouring, the pi should be ready to get taken out from the sand, but if you want to touch it, you must dip it into cold water or wait longer.

Step 7: Finishing Up

The final step is to finish the pi up. After removing the piece that isn't part of the pi, using a handsaw or a cutting wheel, you can start filing every bigger imperfections. Keep filing until most of the pi is clear. After that you can start using the sandsponges and sandpaper from 120 grade all the way up to 600 grade. This is an easy but very time consuming process.

We need cut in a bit to turn the pi into a beer bottle opener. We can use a small grinding wheel to get the job done.

Step 8: Open Some Beer :)

Here's a final video just for you. Thank you very much for reading this instructable. I hope you enjoyed it as much as I did making it. :) If you have any questions post a comment, I'll happy to answer them.