Good questions :) The overall mould size would be 50x50x50mm approx so two halves of 25x50x50mm. The actual part size to be moulded initially is only 8x8x15mm. As for tolerance I guess I would be looking at a minimum of 0.1mm,

It would be intesting to see what results other people have had from a proxxon as it looks like the ideal machine to start to learn about cnc machining

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 might just buy an normal proxxon to get used to it(see if it might be capable of doing what I want), then cnc convert it, at the moment whilst a self build looks tempting I neither have the time or experience to build such a beast.

The bench top injection moulder I have is a Small power machine co SP2 with an air operated piston, my other possible plan is to cast a mould with aluminium powder loaded epoxy resin, but whilst I have heard people talk of doing this on the net I havent seen any results yet,