After putting together the Mostly Printed CNC machine http://www.thingiverse.com/thing:724999 this summer, I have been thinking about other uses of Electrical Conduit Pipe (EMT). I was testing to see if it was possible to run a carriage with V-slot wheels using inexpensive EMT or PVC as the support & movement instead of using the V-Slot aluminum Extrusions. I have included a simple carriage for use with Conduit & another one with PVC as well as some simple brackets to hold the pipe in place while testing. I was quite surprised how well it worked. Since the carriage is offset more than when using V-Slot, using another carriage on the other side of the pipe would help the bolts to stay perpendicular to the carriage. 60mm bolts is probably what is needed to do that with1/2" EMT & I did not have any of those around to test it with yet. The weight of four 1/2" EMT 1 meter long came out to 5lbs. 3oz. You might have to play with the wheel offset dimensions to get the proper fit for you. When I get some longer bolts to test a dual carriage, I will have a better idea of what that should be. A 10' piece of 1/2" conduit here is about $2.50, so you can see the cost savings if this idea works.

You could also use less expensive shower curtain wheels as shown here, http://www.thingiverse.com/thing:1118344 . Looks like these have a 6mm ID instead of the 5mm used with the V-Slot Wheels.

I also added a set of plastic spacers to replace the extra 6mm spacer & three 1mm shims on all the wheels. I made a parametric version of this that can be found: http://www.thingiverse.com/thing:1150496 This idea worked well on an idler pulley I am using on a Delta printer. There is an openscad file for this also, if your spacer needs to be different. I also used M5x40mm bolts for the wheels on the EMT Single carriage. You will probably need M5x45mm bolts for Wheels on 1/2" PVC Single carriage. I added two photos showing the use of the tapered spacer against the wheel & the other side against the plastic carrier. If you use the tapered spacer against the wheel, make sure you use a diameter that will not interfere with the wheel rolling. I initially put the larger diameter against the wheels & they did not roll at all.