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 machine was used for our 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".
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 which is more robust and has a lower bearing count.
The full 360 side of the z-axis uses two bearing assemblies(upper and lower) for a total of 6 bearings.
(3) 624 bearings
(4) m4 nylock nuts
(13) m4 washers
(2) m4 bolt 40mm
This horizonal carriage uses a single flat wooden plate with a central hole for the hot end. It uses four sets of 624 triple bearings mounted in 8 holes drilled in the carriage plate.
This x-carriage is easy to make and very light weight. The low inertia of the carriage and small 624 bearings give this pretty good performance.
It requires that the preload on the bearings be set just right. It was teadious to adjust and setup, but once it was dialed in it ran very smoothly.
The trouble of getting a wrench under the x-carriage to remove the hot-end was the single greatest factor in moving to a vertical carriage in v2.0.