Apparent Z-Banding Driving Me Crazy

Is this amount of banding normal? It appears on all my parts and has ever since I got my machine. I even noticed that it is present on the 3d printed parts for the machine itself.

It is really tough to photograph and it only really visible if there is a light source shining down on my parts from above. I am try to decide if I want to replace my Z lead screws or not. I’m not convinced it would help.

P.S. I have no idea why this damn window shows so many copies of the same image. Yet another flaw with Lulzbot/Alephobjects.

Reach out to the support team, you may want to take a few more images if you can:

I get the exact same thing. If you get anywhere with this issue, please let us know.


Some better pictures, for you reference.

Thanks for the response Randy. I’m thinking it is a bent Z-axis screw. I’ll be sure to let you know if I ever get this resolved. Quite honestly, the reason I got the Lulzbot mini was so that I could have a printer that just worked and produced high quality prints. My 1st printer was a heavily modded Da Vinci. Currently, this print quality isn’t any better than that of my $350 printer, probably worse in all honesty. I’m seriously considering dropping my 3d printer hobby. I can’t tell you how frustrated I’ve been with this. I tried upgrading the firmware, turning the leadscrews so that the software didn’t have to compensate as much, tightening belts, looking for loose bolts/screws, nothing has helped and I can’t even stand to look at the prints my machine produces, the “quality” is complete garbage.

I had read in another post in this forum that there is a design flaw in the mini that causes, Z-wobble. Apparently there is a design flaw in the mini and most Taz printers. The axis is over-constrained by the bearings at the top and bottom of the printer Z-screws, as well as the two metal rods which also guide the Z-axis up and down.

Turns out the original 3d printed parts that are part of my machine also show the same banding (example below). I wish Alephobjects would just admit this is a design flaw, refund my money and stop wasting my time.

You could take the top off and remove the bearings. Thats what I did.

Which bearing did you remove? Both the top and bottom of each of the two Zs? Any pics of surface quality you can share?

It’s pretty hilarious, I asked support about the banding on their own 3d printed parts from the factory and they just said that mine is worse…Personally, I think theirs is probably worse (they are likely printing at higher speeds so it is to be expected). I asked them to tell me if this is a know design flaw which can be resolved but they kept on suggesting silly possible fixes which clearly couldn’t be causing the banding. One was the hobbed gear…yeah…I’m sure it’s a feed rate issue that just happens to occur at the exact same pitch as the z-axis screw.

This will be happen with any printer with lead screws… unless heavily modified. Its the nature of the screw.

Try a sixteenth to eight turn of one lead screw (either right or left), not both screws. The idea is to get the screw contact point in the middle of the pitch opposite to the other lead screw. This would create a more consistent contact… no wobble due to the screws in phase. Anyway this is highly “trial and error”… YMMV

I’ve tried that before, it doesn’t do anything. Also, I have no idea of the mechanism by which that is meant to work, given that the printer is trying to adjust for the bed not being perfectly level. It will be adjusting the different Z-axis screws by different amounts and end up at different positions along the Z-axis screws in different regions of the bed, in any case. Perhaps if your bed is relatively level to start with it may appear to help in a small area of the bed where there are basically no adjustments made.

The two lead screws will move in tandem at all times, even when leveling. There’s simply no mechanism to permit otherwise (there’s only one motor driver, and the two motors are in parallel). So just grasp one of the screws, and gently rotate it 1/4 turn, and see if the banding is less obvious.

Okay, that makes sense. For some reason I thought they moved independently but if that were the case it would change the angle of the nozzle relative to the bed. I’ll give it another shot. Lulzbot support had me trying to dial in my Z-offset height. I have no idea how they think not having your Z-axis dialed in could cause recurrent surface imperfections that match your Z screw pitch.

Is it possible to improve banding by using layer heights that are even steps of the Z stepper motors? If, for example, you have a layer height that requires 10.5 steps, the layer height will sometimes be a little shy and other times be a little large as the errors accumulate. I can see this producing banding.

Does anyone know what layer heights to use to get even steps?


For the mini the screw pitch is 2mm. The motors are 200 steps per rotation and we are using 1/16 microstepping. Therefore the steps per mm is (16*200/2mm) = 1600 steps/mm. So there are 1600 steps per mm.

In other words, Steps = Layer Height x 1600. As an example, 160 steps = 1600 x 0.1 or 320 steps = 1600 x 0.2 etc.

Personally, I think the banding is caused by a very slight bend in one of my threaded rods. I suspect it is the one furthest from the power supply since it appears that there is less protection to banging it in shipping there and the banding seems to originate on that side (i.e. the banding is deepest on that side).

I’m finally making some progress. I was totally incorrect about adjusting one of the Z axis screws not doing anything. I gave one of the silver couplers ~a 1/16th turn with the motors turned off and went from the 1st photo to the 2nd photo.

Glad thats helping. Just be careful not to skew the gantry too much. It could bind at taller heights.

Yeah. Thanks for the tip! I haven’t had much luck getting it any better than shown above. It isn’t terrible though and only really noticeable if go out of your way to look for it. That said, do you know if there is any theoretical sweet spot for the rotation of the screw relative to each other. I was thinking maybe 180 degrees “out of phase” in terms of thread orientation would be ideal. I tried that and it was worse than the second photo. Any thoughts?

Also, do you know the best way to test if your lead screw is bent? I have a sneaking suspicion that lead screw on the side furthest from the power supply is slightly bent, since the banding is at its worst on/seems to originate from this side. Also, this side isn’t as protected and could easily have been subjected to damage during shipping. Honestly, I’d be surprised if Purolator didn’t destroy any precision instrument that it acted as a carrier for.

Any thoughts on whether I’m chasing ghosts trying to get better quality than shown in the second photo above? Could this simply be the limit of the precision of lead screws? Since no lead screw is perfectly straight, there will always be slight wobble.

To be honest, I think you’ve got it pretty close to perfect. At one point, I thought a heavier lubricant might stabilize the travel even further. But decided not to try anything too drastic.

Somewhere along the research path, I read that all lead screws have a slight bend due to manufacturing. After reading that, it really did seem like chasing ghosts.

Testing for a bend… I would resort to the “pool stick” test, lay it on a flat surface and roll it. A bend should be fairly apparent. Of course, that would mean a lot of disassembly. Unfortunately no ideas how to test on-machine.

Ultimately, post processing and finer layers would be the only way to get smooth “walls”. Personally I don’t mind the slight banding… on my machine its only apparent in certain lighting on curved surfaces. A SLS machine would be the only other way to eliminate the banding.