There are multiple mechanical problems to be solved in the conversion of an inkjet printer:

• Locating major parts - Rails (4-5), pullies, toothed belts, bearings, gears
• Thinning and lightening the print armature for easier movement across the print area
• Designing non-leaking resevoirs for printed and reserve plaster
• Constructing a light and strong frame for mounting components onto

To locate your major hard-to-fabricate parts, your best bet is to stick with the same source as your print-armature - printers.  Most printers (and scanners) will contain several gears, a smooth steel rod, and a stepper motor as a bonus.  If you don't have mutliple printers lying about yet, consider googling "electronics recycling [nearest major city]".  Electronics scrapyards will have piles of old and broken printers and scanners awaiting recycling, and are likely to let you purchase mutliple units for very cheap prices.  I have walked out of scrapyards with as many floppy drives as I could carry before, and paid nothing.  Stop by, ask nicely, and you'll probably have more material than you can use.

Thinning the print armature is optional, but probably work it if you can do so without damaging anything.  With less weight, y-axis travel will be easier and faster.  I can't really make any suggestions as to how best to lighten things, other than to suggest dremelling out sections of low value and drilling holes elsewhere with a VERY cautious eye.

Print and reserve resevoirs will evetnually get their own page - current suggestions will be to mimic the design of Graham Stahler.

Frame design will also get it's own page or pages.  I have even less to contribut here so far.