Greetings everyone, and happy new year!
I have a new-to-me Taz 6 with low hours. After a few days of putting it through its paces, I noticed the z axis binding, and a google search revealed that it was a common occurrence. Lubing the z axis screw shafts helps, but it still seems like there is excess friction with the screw nut, especially on the left side. I believe it is caused by off-axis loading from x axis belt tension, as the x axis belt is not in line with the 10mm z shaft, and the x axis shafts are not held especially securely by the set screws. I thought an easy fix would be to add two additional 10mm shafts on the front side of the printer, to unload the off-axis force on the screw shafts. Pictures are below.
The top plates already had holes for 10mm rods in front that mirror the back. The only other modifications necessary were to extend the right hand x axis endstop by about 2mm to prevent the extruder motor from hitting the bearing, and to move the spool holder to the back rail also for clearance. I also cleaned up Lulzbot’s CAD files a fair amount while I was at it, and I’d be happy to share them.
Please provide any comments and feedback!
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Nice upgrade! Have you seen a demonstrable impact on print quality?
Thanks! No difference in print quality that I could tell, though I didn’t do much z-axis testing before or after. There is noticeably less side load on the z axis screw though; before, the left screw bearing was pressed against the side of the cavity in the top plate, but now it is more free and centered; and turning it by hand is easier. Z axis travel also seems quieter, but that could be imagined. I also have the allen screws in the z screw nuts tightened more than they were before, without binding; before, I had to leave them a little loose to prevent binding I think because of side deflection of the screw.
Yeah, Lulzbots seem oddly unbalanced by design in this regard. Igus bearings don’t play well with cantilevered loads and excessive runout. The designs are showing their age, but it’s also a testament to other aspects of their build quality and open source bona fides that they keep chugging along like they do. 
Interesting that adding additional friction elements to the design has possibly reduced friction overall. Please follow-up with how this works for you, and def post files when you have a chance.
My Igus bearings were delayed in shipping, so I actually have LM10LUU bearings currently installed in the new z carriage pieces. I think either should work fine here; the z axis doesn’t travel alot or quickly like the x and y, and the new rods I installed were hardened chromed instead of the stock stainless. If I ever print new pieces to fix minor issues I’ll try the Igus.
The lowers are designed to hold 450mm length rods (instead of the stock 500mm which protrudes through the bottom) which are commonly available and inexpensive, and the rods end up at just the right height.
I tried to attach .stl files for the new lowers (identical left and right) and z carriage pieces, but new users are not allowed attachments. (I first tried to attach .step files because I thought they would be more useful, but they were not an allowed file type.) Until I’m eligible for attachments, if anyone would like either .stl or .step files feel free to contact me at alextlin@hotmail.com.)
I would have hoped that Lulzbot fine-tuned the design in Taz 1 through 5; but since they went with something pretty different in the Workhorse and Pro, I guess they’re still working on it. I wonder how the new design is working out.
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Still no more Z axis binding after 6 months of regular printing, so I think this mod is successful. I’ve added it to Thingiverse: Lulzbot Taz 6 Z axis dual smooth rods (anti-binding mod) by alextlin - Thingiverse
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