Issue with Z axis drive nuts

I have a TAZ 4 that’s upgraded to a TAZ 5.

A week after I originally bought my TAZ I had an issue the where Z axis drive screws would get out of sync and I have seen other posts about this issue with no real resolution.

I of course called Lulzbot and after a few things tested their “resolution” was to back off the 3 screws that hold the nut in place and just leave them very loose. Well it seemed to work as the problem ceased but it does not seem like the “right” way to fix the issue.

Today I pulled my machine apart to add new bearings (ones I have been testing on the X axis for almost 6 months) and at the same time tighten up loose screws, belts and just generally do a bit of maintenance on the printer.

Well, when I got the printing out (it was in an enclosure) I noticed that there was only 1 screw left in the Z axis nut (see photo) apparently the others fell out from being loose.

So I put them back in and I decided to go ahead and tighten them down like they really should be. Made sure everything was very level and setup the Z axis perfectly.

First print work flawlessly up to about 10mm high (the first 10mm looked better than my prints have in years) then the 2 Z axis motors got out of sync and jammed (next 10 layers printed on the same layer and made my 20mm test cube look like a mushroom).

So, I am looking for a resolution to this issue that does not include leaving the screws loose.

Any thoughts?

If something is binding, something is out of alignment, possibly the x axis rods are pulled in or out a bit. I would pull the rods and the carriage off, line up the two x carriages and z motor mounts really well, lubricate the leadscrews, then run them both up and down multiple times to endure they don’t bind and stay parallel. Then reinstall the rods and carriage and retighten.

Just having a serious look at the design I just realized that when you tighten the x belt you can put the leadscrew into a bind. It pulls inward on the leadscrew out outward on the smooth rod. But a tight belt makes for better prints. Hmm…

Oh, and one of the things support had me do (about a dozen times) was move the mech up and down 100-200mm at a time. They first told me to remove the screws movie it up and down 100mm a few times then put the screws back in. After doing this many times they said just leave the screws loose.

I think that is one of the purposes of the smooth rods, to counteract the pull of the belt and applying a twist to the guides on the end on the threaded rods. There is a small range of ‘good’ balance on where the rods are reducing the binding on the threaded rods enough both ways (inward and outward).

I realize now that the X axis rods may play a big roll in all this, when you pull the belt tight these rods ‘should’ take the pressure from the belt as they are tightened down on both ends. So, maybe there is a step to prevent the binding even with a tight X axis belt.

My ‘guess’ would be to remove the x-axis belt tension, loosen one end of both the x-axis smooth rods (so they can freely move) then with the bolts on the Z-axis nut tight move the carriage up and down to allow the X-axis smooth rods to settle in, tighten those 2 rods. At that point hopefully the tightness of the x-axis belt won’t matter much.

Does this make sense?

I wonder in Lulzbot has an actual procedure for something like this.

Yep, you have the general idea. The ohai kit assembly instructions use a series of lulzbot designed alignment templates and gauges to achieve that result on the stock 5’s. Any missallignment at all causes leadscrew binding. For me, I had one of my z motor mounts lower than the other the first time I upgraded my 3 to 5 spec AND I had the x ends too far out. Once I had those correct it printed great.

More testing more findings. (I am determined to resolve this rather than live with it).

It’s got nothing to due with the belt being tight or the 2 smooth X rods.

I loosened the belt significantly (a loop hanging down) and undid the set screws on one end of the smooth rods (X axis) so they could move.

Tightened up the Z axis screw again and it still binds. It has all the slop on the belt and X rods it could use.

Next step:

I looked at everything very closely and noticed the metal plate on the end of the Z axis and the printed plate that bolts to the Z axis nut where not even at the tops of each (slightly askew) so I loosened those up on both ends slightly and no binding. I then held them so they were the tops of each were much more inline and tightened them down.

Now, the binding has been significantly reduced but not eliminated. Before the left motor would move a ways then just shudder and stop (the right one would keep going until everything slipped or I hit stop. Now with everything tight it moves without stopping but the left motor is complaining (slight clicks on direction change and vibration on occasion)

Two other things I did try was to loosed the bolts on the left motor and move the Z axis up and down then tighten them (in case it was being forced off to one side slightly) then I loosened the set screws on the left Z coupler, gave it a good wiggle to assure it was not in a bind then tightened them up again. These 2 things did not seem to make any real difference.

Doing a test print now but I can still here the left motor groan on occasion. Maybe it’s a bad motor as well and whatever bind there is may not be an issue for a good motor?!?!?

Next thought is to loosen, wiggle then re tighten all the screws on the left metal plate that connects the Z rods, Z nut and bearings to see if that makes any difference.

Any other tips?

Start from the leadscrews out. Make sure the z motor mounts are all the way up, and there is no leadscrew up or down motion. Then check the z motors for proper position in the motor mount. The x end plates need to be square to themselves and to the leadscrew. The distance from the bottom of the leadscrew nut to the top of the leadscrew lower bearing should be identical on both sides. The coupler needs to be on the flat spot with the setscrews and down tight. The gap should be the same both sides. Treat the side with the z endstop and x motor as the reference location, and make sure the x end plate is parallel to the frame, the rods are locked in on that side and the two x end plates are parallel to eachother front and back. After you run the x axis up and down a few times, then lock down the idler side rod bolts.

Check the heat set inserts on the leadscrew nuts. If they are at all too high, you can be off by that amount, which could be half a thread. Remove any mushroomed out plastic. Make sure the nut mounts and bearing blocks are lined up on the x ends the same.

Check the ohai kit manual for the kittaz installation, it was aimed at home assemblers.

Maybe post some pictures of the x ends and leadscrew ends, one of us might notice something?


I might have gotten it fixed.

I was very curious about the leadscrew on the left so I took the motor out and unscrewed the leadscrew nut to see if the leadscrew would turn freely in the bearings. It was a little stiff so I just kept turning it and it freed up quite a bit. I then turned the leadscrew nut on it’s own, those things have zero slop and take a little effort to spin but I can see how that’s a good thing.

It turns out I did not know the Z coupler had 2 set screws so last time I only loosened 1 of them (this may be the fix) and so I installed the motor back in, tightened up the Z nut and then lastly the Z coupler. So far I don’t hear any oddness out of the left motor but I will reserve judgement over time since when I first got the printer it would only screw up every 10-20 hours of printing or so.

I think maybe the motor was pushing up a bit too hard on the leadscrew and this might have put the bearings under pressure (why they turned a bit stiff to start but then easily started spinning freely. At least I hope that was the issue.

I am learning lots on how the printer was designed and built doing all of this and I am not afraid to tear it apart as I am pretty sure I can always get it back together properly.

I will post back soon if it fails again or in awhile when I think it’s totally fixed.

First 20mm test cube.

Nice job! now you can tear it all apart again and modify it haha!


Already done some mods, thumbscrews to level the bed, LED lights on the bottom of the top frame, 40mm fan on the hotend, PEI bed and the latest is the teflon bearings (really bushings) that fit the rods with far, far less slop than the original yet glide so smooth it’s not even funny.

Reporting back. The binding has not returned. It seems the motor was pushing the leadscrew up to hard and putting the bearings into a bind so releasing that pressure by loosening the Z coupler and giving it all a good jiggle then tightening it back down did the trick.