There's not much activity here, but here goes.

I've got a Shopmaster, and would like to do some additive machining work using it as my base. I know practically nothing about SLM, and might consider going with sintering instead, if melting is too difficult. However, I want real prototypes that can hold some force, and that means aluminum or stainless. I'm not interested at all in a plastic prototyping machine.

What I know:
CO2 laser, on the order of 100 watts.
Some inert environment like Argon.
Some sort of powdered alloy
Some sort of mechanics to spread the powder layer.

So, I suppose I'd have to make at the minimum a box that will absorb all stray laser power. How does the bed of the machine not get burned away? Does the laser lose focus over distance and make this a non-problem?
I see that there are lasers on Ebay on the order of about $2,000 that would seem to fit the bill. Any knowledge there?
How long does this process take? How many inches per minute?
Where does one purchase the powdered alloys?
It seems to me the biggest difficulty would be keeping the optics clean.

Why don't I see many diy websites on this? I would think that this would be a pretty popular thing as a step above the FDM that many are doing with plastics.