Casting Aluminium Pencil by Using a Microwave and a Vacuum Cleaner

I casted a working metal pencil by embedding a graphite core in the cast.

Graphite can withstand very hight temperatures, so I wanted to see if it's possible to do it without breaking it.

In this Instructable you'll see me using unusual techniques of metal casting, burnout and vacuum casting.

I will briefly explain what I am doing, but I won't go into detail.

We'll keep this Instrucable about the pencil. The same result can be achieved by using traditional metal casting methods.

I will publish separate Instrucables about Microwave Metal Casting, Using Microwave Kiln to burnout moulds and Vacuum casting with a vacuum cleaner.

First I printed a simple PLA pencil

I wanted to try to embed a graphite pencil inside of aluminium when doing the metal casting.

Graphite pencil cores are made from graphite and clay mixture. Idea was to do Lost PLA casting and pour hot aluminium over the graphite core. I inserted the core inside of a PLA pencil.

I attached the pencil to a 3D printed flasks bottom with a cheese wax.

To make sure I could release the plaster mould from the base without breaking the feet, some Vaseline was applied.

Then I put it in the freezer for the cheese wax to harden.

After that, I joined the flask with the bottom and secured it with binder clips and electrical tape.

For the investment I used: Plaster of Paris+Fine Sand+Water.

I vibrated the mould with reciprocating saw and after that left it to cure for around 1h 20 minutes.

I carefully removed the flasks bottom, trying not to break off the feet.

I recovered some of the cheese wax before putting the mould into the oven.

Before I start burning out the mould in my microwave kiln, I used an oven first.

I don't like to put wet mould into my microwave kiln as it can get damaged. Also, it's way easier to work out the burnout cycle if you use the oven first.

I will use a microwave kiln to burn out the mould.

I already published an Instructable on Microwave kiln making, but I don't recommend making it that way anymore.

I have a new microwave kiln Instructable coming out very soon.

Microwave kiln will heat up the mould just like other types of burnout ovens, but one thing that's different is microwaves.

Microwaves will crack the mould (in most cases) before you have a chance to finish the burnout.

An easy workaround is to wrap the plaster mould with an aluminium foil.

I like to use a 3D printed pin roller to make a lot of holes in the foil, so the moisture could escape.

The foil will prevent the microwaves from reaching the mould.

I have a large microwave kiln that I use as a burnout kiln.

I put the mould into the kiln on top of a small foil sheet.

Then the kiln was placed in the microwave.

How can you control a microwave kiln?

I use a "cycle timer". It's a timer where you can plug in your microwave (or something else) and choose ON/OFF cycle.

It will only work with analog microwaves as digital microwaves stop working when you kill power.

After many, many experiments and temperature measurements, this is the cycle I use for a Plaster mould this size.

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1 minute ON

6 minutes OFF

I run it for 4 - 5h without doing anything and the mould burns out clean.

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After that, I may or may not ramp up the temperature by changing cycle to 1:5, 1:4, 1:2 etc.

Total burnout time including the oven: 7 - 8h

I use a vacuum cleaner to do vacuum casting. It works pretty good for basic casts.

There is a reason my plaster mould was exactly the size it was...so I could vacuum cast it by using a coffee filter method (I just made up the name)

Procedure is simple. All the moulds are made to fit a coffee filter funnel.

It's a coffee filter from an Italian moka pot.

They come in different sizes. I use 3 cup, 6 cup, 9 cup, 12 cup.

The "3" cup filter is the one I use the most.

The funnel sits on the table connected to a vacuum cleaner with a silicone hose.

I used my homemade crucible and insulating chamber to melt aluminium pencil sharpeners in the microwave.

First I took out the microwave kiln and set it aside.

The mould will stay warm until metal has been melted and ready to cast.

When the metal was almost molten, It was time to prepare the mould for vacuum casting.

I took out the mould and removed the foil. The mould was between 350°C - 400°C.

I could had ramped up the temperature, but I chose not to. My moulds are usually between 350°C - 500°C. I rarely go higher than that.

I put it inside the funnel and pulled up the silicone sleeve.

I turned on the vacuum cleaner and poured the metal.

When the mould had cooled, I rolled down the silicone sleeve to take out the mould from the funnel.

Then it was opened.

Then it was time to clean it up.

I used an ordinary pencil sharpener (and 2 extra blades) to sharpen the aluminium pencil.

It was not the easiest pencil to sharpen :)

I chose not to try to sand out casting imperfection - pinholes. I think it makes the pencil look better.

I believe the pinholes were caused by gasses trapped in the mould. Usually, I turn the mould upside down in final stages of burnout, but I did not do it this time, because graphite absorbs microwaves, so I did not want to take chances.