Shown here is a generic printed axis. I designed and printed this one today to be the Z-axis for a Stereolithographic UV 3d printer I'm making. I will upload more progress about the printer as I make it. This axis seems to work well enough. I used 3/8" steel rods and bushings, because that's what I had laying around. I also used 1/4" 20tpi threaded rod. The SCAD file is generic, so you can change a few variables to make it 1/4 - 8mm rod compatible. I also used piece of plywood as a base.
I built the axis to be 300mm overall length, you can choose any length you'd like. I would recommend using an lm8uu or equivalent for your rod diameter instead of bushings. When you change to lm8uu's or other, you'll need to adjust the slider to fit.
12x 5mm bolts, washers, & nuts
1x 608 bearing
300mm 8mm-threaded rod
2x 300mm 3/8" steel rod.
3/8 ID, 1/2 OD brass bushings (2 or 4)
anything else I forgot to add.