Just one week ago I made a laughable gaffe in suggesting, in an obscure reference to uranium enrichment, that I should use Aluminum tubes to form my graphite "lead".
Wrong! Graphite is corrosive when it comes in contact with aluminum. Maybe that's the real reason that NASA uses pens in space.
Also, Graphite is a very different thing in a zero-g environment, and I must be careful when milling graphite. Don't inhale!