Re: CNC Router vs 3D Printer
 

You are looking at the "3D Printing Revolution" through a very jaded lens. Allow me to walk you through the process I'm going through right now for some structural parts:

Step 1: CAD Parts
Step 2: Print Parts
Step 3: Assemble parts
Step 4: Simulate loading to failure
If acceptable failure continue, else go back to Step 1 and iterate.
Step 5: Depending on part produce part a mold or make on router/mill

Because I have the 3d printer (and can run it unattended) I can hit print and go work on other things. This means I can iterate a lot faster on parts. And sometimes it's far easier to see problems with a design when you can hold it in your hand.

If you look at it as the end of the manufacturing process it's fairly useless. If you look at it as a step in the engineering process it's much more useful.

Re: CNC Router vs 3D Printer
 

I agree with you here, that is why they are referred to as a "rapid Prototyping machine" meaning they are not meant for major parts only quick samples and models of a practical part.

I would also like to mention that a CNC router can be really noisy and depending on where you live in college (i.e. A dorm or apartment) this may be a problem. I would also say that a router is more 2D objects that you would have to use other tools for to bend and shape defeating your purpose. 3D printing would most likely be the best way to go for college at least.

Re: CNC Router vs 3D Printer
 

Have you considered a roland SRP? http://www.rolanddga.com/products/scanners/mdx15/

The mdx15 is roughly in the range of the 3d printers that you're looking at. It might be a bit out of your budget, but it can do aluminum, and according to the manufacturer produces better tolerances/surface finish than a 3d printer, especially the ones that you can afford

Re: CNC Router vs 3D Printer
 

I used this machine several years ago. Honestly, it's a joke. Your money is better spent elsewhere.

Re: CNC Router vs 3D Printer
 

You could always try a totally different approach to get machine shop access.

Throughout college I got jobs working in and running labs and shops. Not only did I have fun jobs during the school year that paid decently, but I developed good relationships with the machinists and other lab/shop personnel. I (and a few others like me) were allowed to use various shops after hours and on weekends, when they were not normally open. One year I ran the ME prototyping lab (talk about unfettered access!) and my senior year I was empowered to start a welding lab. I wound up teaching a number of faculty and many students how to weld and was invited to sit in on the ME staff meetings as an adviser. I never had any issues getting anything made in a timely manor. It's amazing what a good relationship with the powers that be will get you.

TL;DR: turn your cash flow around by getting a job at a shop or lab in your school, play nice and earn trust to get expanded access, learn how to manage a shop (schedule, budget, safety, etc), balance competing interests, and wind up with some great experience.

I assume, of course, that this sort of thing is an option for you. You might need to set a precedent, but you'll never know if you don't try.

Re: CNC Router vs 3D Printer
 

Could an arch-welder head be used as on a 3D printer?

Re: CNC Router vs 3D Printer
 

You can use a similar CNC technology and a proper table (think plasma table) to do 2D robotic arc welding. Many industrial welders use robots.

You are probably closest in thought to laser sintering, which uses lasers to form layers in metal powder as in a 3D printer.

Re: CNC Router vs 3D Printer
 

Could it? Probably.

Is it going to be useful? Possibly--most 3D printers that could be modified for an arc welder tip are under a foot of travel in any direction, which may or may not affect usability (though it'll certainly affect size of parts that can be welded). Also I can't think of anything that would need that much precision (we're talking in thou here) in terms of arc welding. Might want to try a CNC router modification first.

Is it a good idea? No. There's a lot of stuff that could go wrong, ranging from melting plastic (reprap-type machines) to warping the print surface (VERY bad if you ever want to change back) to any other safety concerns with exposed welding.

As stinglikeabee pointed out, you're pretty close to sintering, but those types of 3D printers are a minimum of 6 figures, not counting material cost--and in some cases, shielding.

Re: CNC Router vs 3D Printer
 

Are you looking for the same print quality? And what are your limitations on build space? I have the privilege to be an intern at the Manufacturing Demonstration Facility, a part of Oak Ridge National Laboratory, in which I mainly work with a variety of consumer printers. We have two uPrints, and the quality is amazing, but I have found that the Afinia printer can have almost equally amazing print quality and it is below your range in price. Although, the build space is only 5x5x5 in, so it depends on what you are working on. As far as structure goes, I have been using HIPS, or High-Impact Polystyrene, with the Afinia for a while now and it works great. It isn't Ultem, but I think it is an upgrade from ABS. It takes minimal tinkering, and fits very well in a dorm room. Also, I have quite a bit of experience with the Makerbots and the Solidoodle 3rd gens, so if you have any questions, feel free to ask.

Re: CNC Router vs 3D Printer
 

Speaking as someone who has used a CNC router table to do MIG welding development... it's not a very good idea. The arc root can jump around, the material is laid down in a non-uniform profile, and there isn't much of a practical way to make 'filler' to support cantilevered features. Weld beads simply aren't consistent enough to get a decent part or hit any meaningful tolerance.

Robotic welding is used quite a bit in industry, in very but "not 3D welder printing."

As other's mentioned, printing in metal means SLS or another comparable process using powdered metal. Though this area is ripe for innovation...