Hi,
I am noticing an issue with our fairly new TAZ printer. The Z axis seems to be sticking or binding between the vertical smooth rod and white “fingery” bushings on the righthand side. The result is that as the Z height is changed, the righthand side of the Z gantry stays put for a short while after the motors start to move (the height change is taken up by the printed wave spring, which deforms slightly), then suddenly jumps up or down. The height after the jump is incorrect (some deflection still on the wavespring), causing the bed leveling to effectively be off from one run to the next. The (hysteresis / backlash / stiction) is always on the righthand side, regardless of the position of the extruder, so it doesn’t seem to be a weight / gravity issue.
The smooth rod is clean and free of debris, and there have only been a handful of prints done on this machine. The manual also warns not to apply lubricant. Is there an adjustment or other recommended means to fix this?
A couple things to check. There are two threaded rods, one on either side of the TAZ frame, that control up and down movement. If one of those rods is turning at a different rate, or not turning at all, you will see that happen. Check the couplers from the threaded rod to the motors and verify they are tight and the zip ties are intact. Also check and make sure that the rod itself is able to turn and isn’t bound up on one side inside the ACME nut. Make sure the couplers aren’t getting hung up on anything either.
Another thing that can cause binding is if the X carriage is already out of level significantly. Check and make sure your carriage is not up on one side more than it is on the other by measuring from a common point down to the motor mount. if it is off, this can put friction on the threaded rod and cause it to stick. To fix that, turn the threaded rod manually on one side until both X ends are level, then re-home the machine and try running back up and down the Z axis a few times.
If that all looks like it is working, make sure both motors are cabled correctly and there are no nicks or breaks in the cable
1013’s dual Acme nut X ends will also prevent such issues from happening in the future, though you’ll want to get your existing X ends working before you upgrade.
Hi piercet,
Thanks for the advice. I had previously leveled the carriage using a spirit level relative to the frame and Y smooth rods, but it measures out as level too. The couplings to the motors are both tight and the motors/rods seem to turn at the same rate.
It seems like the problem is at the interface between the white bushings and the smooth rod, given that the wave spring holding the threaded rod develops enough tension to visibly deflect before the axis position “breaks loose”. Could it be the opposite of this problem? (https://forum.lulzbot.com/t/taz-very-loose-solid-rod-bearings/112/1)
It could very well be a sticky bearing. What I would do is literally pop the bearings out of the holder and see if they run smoothly up and down the rod. You should be able to move a bearign with your pinky finger with minimal force. if it works fine out of the bearing holder but binds in the holder, call tech support and see if they can send you a new one or something if it is under warranty. It’s also possible that the X carriage rods are spaced too far apart and the assembly is pushing out on both sides, causing the bearings to stick. To check for that, loosen the bolts holding the X axis rods top and bottom on one side to let off any excess force, then retighten and see if you have the issue still.
if you have some funds available, get some ball bearings to replace the solid bushings…imports are not too expensive, and seem to work fine for this printer.
To check for that, loosen the bolts holding the X axis rods top and bottom on one side to let off any excess force, then retighten and see if you have the issue still.
Aha, you are a genius! I didn’t even realize where the rod holder bolts into the frame could be adjusted / slopped around so much. The “stickiness” was occurring at the bottom of travel, but not at the top. Loosening the 4 bolts on the bottom smooth rod / motor holder, giving it a few love taps at the bottom of travel until the up-down motion was smooth, and re-tightening seems to have done the trick. Thanks!!
@1013 - Everything seems to be good (or good-enough) now, but I am intrigued. What kind of ball bearing (size / part#) can they be replaced with?
Glad its working for you now. I ran into that same issue the first time I installed the new x ends on my printer so I know how difficult that one can be to find. I figured it out the first time by accident.