Machine design

I'm wondering if anyone has any experience in producing machines,
such as mills and lathes? I think it would be a lot of fun to produce
my own machine from scratch (well, not entirely, but mostly).

Right now, I'm thinking about some kind of small horizontal machining
center. You don't see very many (any?) of these in a small package. I
understand they're usually used for large production runs, but they
would be good and affordable for smaller shops, or people who have a
product, and need to manufacture some parts for it in their basement.

I like the idea of a HMC because of their (potentially) smaller
footprint with a bigger workspace, and the inherent advantages
present with HMC's (chips not being cut twice, etc).

Some ideas about the mill are as such: The mill would have an
envelope of something like 12X12X8" or perhaps a bit larger. The
machine would be more suited to aluminum and other soft metals,
although it should be able to cut steels (very important). A custom
spindle would be produced to accept some type of standard tool holder
(like ISO-30 taper, or smaller). The system would include an auto
tool changer, and auto pallet changer. I was thinking about custom
box ways because they look so gosh darn easy to produce (milled,
ground and lapped, or perhaps just ground steel flat stock?), yet
very stable.

The machine's super-structure would be based on steel square tube,
probably concrete-filled for vibration dampening. Someone recently
mentioned mounting everything on a granite surface plate, which can
be had for, usually, $50 or so for a good sized one. I really like
this idea.

I'm playing with the idea of having the X and Y axes on the box ways,
and just having the Z axis as a quill.

Obviously, this would not be a dirt cheap machine. However, I would
like to keep it simple and robust (like the Taig systems) - and very
much capable doing work within its envelope.

Does anyone have any comments on such an idea? Perhaps I'm just off
in space right now, but it's certainly something to consider.

Regards,

Robin