Hello!! It's Joseph

demo-ing the different materials you can use:

 lead screw (above) and threaded rod (below) Threaded rod is, after all, not made to be used as a precise positioning tool. It is built to fasten and to remain stationary at all times. from ProtoParadigm:   If a printer does use threaded rod for motion, the results will generally be better if the rods are suspended from the top  of the printer ( as in a common Prusa design ), supporting weight in tension rather than if the motors are on the bottom ( see the now outdated Mendel design ) holding the rods up and supporting weight in compression.   Keeping the rods in tension rather than compression will minimize bowing and bending, though a bent rod can still cause problems .  While the deflection from compression may not be very visible, you can bet it's playing a role in your accuracy when your carriage is near the top.  Many printer designers minimize the compression issue by using very large diameter smooth rods that are mor...

from Lavith, on thingiverse thrust bearing to be used:

XSD i3 using quality test as in Makezine  dimensional accuracy: bridging overhang retraction negative space XY resonance

Name Total Score $ Price Vertical Surface Finish Horizontal Surface Finish Dimensional Accuracy Overhangs Bridging Negative Space Tolerance Retraction Performance Support Material Z Wobble LulzBot Taz 5 35 2200 5 5 4 5 5 2 5 2 2 Zortax M200 34 2000 4 5 5 5 5 4 4 0 2 SeeMeCNC Rostock Max v2 33 999 4 4 4 4 4 5 4 2 2 Fusion F306 32 2975 4 4 5 5 3 4 5 0 2 LulzBot Mini 32 1350 4 4 4 5 4 3 4 2 2 Deezmaker Bukito 30 849 4 5 4 2 3 4 4 2 2 PowerSpec Ultra 3D 30 799 4 5 4 2 3 4 4 2 2 Ultimaker 2 Extended 30 2788 4 5 5 1 3 4 4 2 2 Ultimaker 2 Go 30 1335 4 5 4 2 3 4 4 2 2 BeeInSchool ...

from 3DPrintingIndustries The 3Doodler 2.0 , ~$50 LeapFrog 3D Ultimaker 2 series XYZ Nobel 1.0 sla AirWolf 3D AW 3D HDL: FSL3D NEA 3D Robo 3D 3DS CubePro C 3D Printer Spectrom

MarkForged Mark One How they do it: techcrunch at CES2015: