This is a design for a /really/ inexpensive linear axis mechanism for an open source selective laser sintering 3D printer that I've been designing (but it should be generally useable for anything that requires a one or two axis system). This is a follow up to the selective laser sintering alpha one dual Z tables that I recently posted ( http://www.thingiverse.com/thing:3390 ).
The innovations in this system are its extremely minimal vitamin count -- only a handful of bolts, washers, and nuts are required. It also uses several long pieces of kapton tape as a linear slide bushing, to dramatically reduce friction and drag (though regular old scotch tape may work just as well ;) ).
( the design was prototyped with 3mm material, but the material thickness isn't critical to the design ).
The bolt holes should snugly fit 6-32 bolts.
Update (from some questions recieved from folks who have made it: )
The width of the top plate (the one with 13 screw holes + 1 shaft hole, and the big curvy notch at the bottom) is 95mm wide by 102mm high, to help get your scale right.
The steppers that Iâ€™m using are KP35FM2-035, which I get at Sayal Electronics ( http://www.sayal.com/ActionIndexP.asp?ID=162138 ), which has a bunch of stores in and around toronto, ontario, canada (and also an online presence, I think). These typically go for about $5, and I think they have a NEMA-14 footprint, with a 5mm shaft diameter.
All the bolt holes are sized to snuggly fit 6-32 bolts, and you will likely have to tap these if you're using a material like acrylic (you can typically self-tap them with the bolt itself through a softer material like hardboard). The bolt holes are 3.4mm dia, while the gear hub holes are 4mm in diameter, making the gears loosely fit (and have a bit of play to find their place -- but you could certainly try cutting the gears with smaller holes to see if that works better). I used 3/4 inch length bolts, but some (for the gears) protrude out, so 1/2 inch would probably be more appropriate for these.
I put a small washer on the underside (but not the top) of each gear to dramatically reduce the friction -- without the washers, the hardboard version doesn't work very well at all, but with them it works quite well. In addition, between each of the structural plates, I placed washers to give a little extra travel height for the gears.
I have added two SVG files with the parts already layed out, that I used for laser cutting. There are some extra gears in there, just to fill out the space. I just put them in a ziplock bag full of gears for later tinkering, or give them away to friends who think they're the coolest thing ever :)