Proxxon MF70 for making injection molds

[Jonathan]

I could ask my dad to hand mill the overall mould dimensions then use a proxxon to do all the intricate work, or my other thought was to machine the mould out of brass which would machine better but might not be as good for the injection moulding bit,

I think that could be a good way of doing it. The main problem might be finding a CAM program that can generate toolpaths from a partially machined item. If your dad can get it close enough that the whole thing can be machined on one or two passes then it could be efficient. If there's too much material left then you've got to work out where it is and add roughing operations to remove it - doable even with a simple program like cambam, but tedious if you have a lot to make.

Brass can be much quicker to maine (SMM is very high), however you're limited by spindle speed and the cutting force...

Beware, aluminium can be a PITA to get a decent finish on, especially if you haven't done it before (esp if you try running high speeds / feeds, or take big cuts).
If you're doing ali, keep some paraffin as a coolant.

And equally if you feed it too slowly the cutter may rub and leave a poor finish.
I think paraffin could be bad for the machine, having such low viscosity means it's going to get into everything.