Question Horizontal Lines Issue

[zach778 0]

Hello! I am new to 3D printing and I am having this issue that I can't figure out. 
I am trying to make Lithophanes for my grandma, but I've noticed on my last two litho prints, these horizontal lines appear near the bottom of the print, but then seem to go away after a certain point. 

FYI, I have an Ender 3 Pro. 

I thought it might be a physical print issue but I noticed in Cura, the lines seem to appear on the BACK of the model, but aren't visible on the front. But the lines do just about line up with where they appear in the final print. 

I have included images of the actual print, the model showing the lines, and the model/image settings I have set for generating the litho model. 

Any help resolving this issue would be greatly appreciated. 

Thank you!

[gr5 2,070]

So there are many possible causes of horizontal banding. 

 

temp

 

One is temperature swings if the nozzle is 5C hotter for one layer then it will extrude a bit more and a layer sticks out.  Then if a layer is 5C cooler it will stick in.

 

z movement

 

But the most common cause by far is Z movement issues.  If the Z axis moves just 10% more than usual when going to the next layer then you get a layer that is 10% underextruded because the distance from the nozzle to the print is farther than normal.  Then if the next layer the Z axis moves 10% less than usual you get an overextruded layer which sticks out.  Layers that stick out and stick in by a little bit causes the banding you see.

 

The quick solution is to clean your z screw.  Spend 5 minutes with a toothbrush and some wd 40 sprayed on the toothbrush (not the the screw as some will get on the print bed!).  Or just use a paper towel and a toothpick.  Clean up the few cm that are used for the bottom of your print and these horizontal lines should go away.  I recommend printing a test print 1cm by 1cm by 10cm tall before and after cleaning.

 

Sometimes cleaning is not enough and you need better quality z screws and nuts.  There was a time when Ultimaker had 50 cent Z nuts and if you moved up to the 80 cent z nuts the quality was so much better.  Z rods and z bearings can also cause binding and issues with stick/slip.

 

Sometimes putting a brick or lead weight attached to the portion of your printer that moves up and down can help as well but this is just a debugging tool and not a permanent solution.  This can reduce stick/slip issues.