1X2 Drill-press Mendel
The Drill-press Mendel v1.0 is a Wood Repstrap that strives to use standard Sells Mendel hardware in the same dimensions and part counts. The design goal is to bootstrap to a printed Mendel with only access to a drill-press and hand saw.
This is the design shown at Makerfaire NY 2010.
This was also used in the Printable Transistor Project.
360 Bearing v1.0:
One of the more difficult assemblies to reproduce without 3d printing is the z-axis 360 bearing. This is a 360 degree bearing assembly with adjustable tension that requires only two holes in the same plane. It also has a small amount of overhang, which allows it to fit between the rail and leadscrew.
How it works: As the "draw-down" bearing is tightened, it presses against a wider chord section of the round rail. This wedge effect tightens the rail against the opposing "capture bearings".
Video of this bearing system being used for all axes to drive a plotter head: <videoflash type="youtube">TWHRB0HDAcs|320|240</videoflash>
Ball bearing "jet-rails" are less sensitive to shaft tolerance than brass bushings and have low stiction. Switching between 8mm and 5/16" can be done with simple adjustment.
It worked, we did some cool stuff with this robot and it is still going strong. This bearing system was designed to only be good enough to print out it's own replacement, but it actually worked better than expected and operated consistently over a long period. With bent leadscrews in a fixed Sells arrangement, the singled sided 360 bearing flexed and did not oppose wobble. This is generally true of the standard Sells 360-180 bearing design as well. This design has been succeeded by 360 bearing v2.0 thingiverse.com/thing:6243 which is more robust and has a lower bearing count.