Since the topic of CNC mills has raised its head here, I thought I'd share this with the DIYDrones community.
One of the things those who are considering this need to be aware of is that the toolpathing of complex shapes isn't a trivial exercise. I would be interested to know if anyone has experience with any open-source surfacing toolpathing packages - please comment below!
I am fortunate to have access to MasterCAM V9 - old-fashioned as it is - but only in a 2.5D package. I then butcher my SolidWorks models into such a form that I can generate an IGES wireframe which represents the basis of a toolpath. I then import this into MasterCAM and labouriously reconstruct it into a contiguous chain which the 2.5D recognises as a contour path. This generates an absolute monster long .NC file which I drip-feed into the Siemens Sinumerik 820D controller that runs the mill I'm using.
The other critical point to this type of work is the machine envelope is everything. Once you start using multiple setups to accomodate an oversize workpiece, you are adding hours and hours to the project, not to mention a bunch of risk and the inevitable mis-match of complex surfaces which will need filling and hand finishing.
As far as MDF goes, it's absolutely not a bad material to machine and is an easily hand-worked end-product which can produce a perfect finish but I do worry about the health risks and it does make an unholy mess. I'd consider using PVC or, if you can afford it, alumnium billet. At approximately AUD10/kg, it's not cheap though...
So, after going of half-cocked with the making of this plug, I have since revised the design pretty significantly, so now it's only a learning exercise and a lovely desk ornament! C'est la vie!
Anyway, I hope this is helpful and interesting.