Diagonal Brace Patch
Date: Jan. 17 2010
Authors: Mo Chen, Bing Dai, Jacob Bayless
Nophead upgraded the original diagonal braces by removing the set screws, and replacing them with an interference (squeeze) fit. While this has advantages, like fewer set screws and 21% less printing time, the disadvantage is that interference fits require precise tolerances; printing the holes a little too large makes the fit too loose, and a little bit too small makes them impossible to attach (although they can still be drilled out). Also, the change is not documented in the twiki Darwin assembly instructions, which makes no mention of them. New Darwin builders might mistakenly drill them out too large, not knowing it's meant to be an interference fit. (This happened to the authors, which formed the motivation of this patch).
The solution: Cutting a ~2mm slot in the part creates a simpler and more robust way of attaching the bracket to the smooth rod. The bracket slides on loosely for easy assembly, and is then tightened by the turning the bolts on the threaded rod. While we bandsawed our parts to create the slot, the new design is also quite easily printable. In fact, printing it assures that the tensioned areas (pressed tightly around the smooth rod) are in the strong plane of the laminations, while the compressed areas (bolts) squeeze the weak plane of the laminations, an ideal orientation.
(No .STLs exist for this yet, but they should be quite easy to make).
Credit for the idea goes to Prof. Chris Waltham of the University of British Columbia. (It appears that corruptedjasper thought of the same thing, too).