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PLA prints have lines

Jess
 Jess
(@jess-2)
Community Manager Admin

* Posting on behalf of a member* 

I have a problem with my PLA prints where some "lines/gaps" show around them, mostly where there is a top layer, as if the layer became thicker (or thinner) than the other ones. I have tested various colours and PLA brands as well as various STL models, however, this problem keeps showing in every case.
 
I have printed in temperatures between 190~210 °C; 20~70 mms in speed; flow at 80~100%; bed heated at 60°C; layer height at 0.2mm and fan speed always at 100%, except for the bottom layers. My bed is properly level, and my nozzle and PTFE tube are new and clean.
My printer is an Ender 3 PRO and I tried using both Cura and PrusaSlicer.
 
Attached, you can see pictures of the pieces I have printed so far.
 
Thank you for your attention,
 
Best regards,
George M.

 

photo 2021 01 22 23 28 47
photo 2021 01 22 23 28 44
photo 2021 01 22 23 26 10
photo 2021 01 22 23 23 31 (2)
photo 2021 01 22 23 23 31
photo 2021 01 22 23 23 30

 

 

Quote
Topic starter Posted : 25/01/2021 9:35 am
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi Jess 🙂

Since the lines have remained consistent despite changing slicers, settings and prints, it points to a mechanical issue with the printer. On CR-10/Ender style designs, there are two common causes for these lines - the leadscrew and the bearings for the z-axis.

Leadscrew troubleshooting:

  • Make sure the screws holding the brass nut to the carriage are loose enough to allow it to wiggle a little. This is how Creality permit the printer to have slightly bent leadscrews without binding. If these screws are tightened, the z-axis will most likely bind somewhere along its length (on my CR-10 mini the top half of the z-axis gets greatly increased friction if I tighten these screws too much).
  • Clean all the grease off the leadscrew and re-grease it. Sometimes blobs of grease collect in parts of the leadscrew and cause some artefacts on the print
  • Make sure there is some space between the bottom of the leadscrew and the motor shaft when the coupler is tightened. If the leadscrew and motor shaft are butted up against each other, the coupler can't do its job of absorbing any slight angular misalignment between the motor axis and the leadscrew axis. There should be a 3-5mm gap to allow the leadscrew to flex freely.
  • Similarly, at the top, the leadscrew should be held in place by a ball bearing or other assembly that permits a couple of milimeters of left/right/forwards/backwards motion so that the leadscrew can wobble in place if it's not perfectly straight. If restrained (for example by a printed top mount that does not allow any play), any leadscrew wobble will put artefacts on the print.
  • If all else fails, undo the coupler's grub screw, take the leadscrew out (unthread it from the brass nut), turn it upside-down and reinstall it. This will place the defects that are currently about 1-2 cm off the bed at the top of the leadscrew (maybe 248-249cm high), which is an area you will encounter much less frequently than the first few milimeters of travel. If this solves the problem, you can either leave it like that, or buy a new leadscrew (and hope the new one doesn't also have defects).

Bearing troubleshooting:

The z-axis moves by means of 6 plastic wheels running on the v-slot extrusions of the vertical beams of the frame. You have 3 wheels on each side.

  • Start by moving the z axis up and out of the way (by jogging or sending G1 Z200)
  • Carefully examine the frame on both sides, and use a cloth to wipe away any dust or debris on the extrusions where the wheels ride. Naturally any small piece of dirt there could cause the wheels to stick slightly, and will affect the gantry's motion enough to cause observable defects in the print.
  • Once you've verified the rails are both spotlessly clean, turn your attention to the wheels. Using moderate finger pressure, try to turn the wheels. There should be enough friction between the wheel and the frame that you can't turn the wheel (key word being moderate finger pressure - naturally if you twist it with all your strength you'll manage to get it to slip regardless of whether the pressure is correct or not).
  • If any of the wheels are turning freely in the above test, adjust the eccentric nut for the wheels of that side (left or right) with the spanner that came with your printer. Turning the nut one way loosens the wheels, the other way tightens the wheels. Normally it only takes a fraction of a turn to achieve correct tightness. Remember one wheel is working against the other two so only one wheel on each side has the eccentric nut (the one inside, closest to the bed) so by turning that, all three wheels on that side get tighter. This video explains everything on the Z-axis of a CR-10 (which has the same mechanism as an Ender 3) - https://www.youtube.com/watch?v=X7DN7260JvA
  • NB: do not overtighten the eccentric nuts, because if they're too tight it will make the plastic wheels wear out rapidly (they'll develop a groove where they contact the aluminium of the frame) and then you won't be able to tighten your wheels any more down the line and will have to replace them.

That tackles the large horizontal lines. The light vertical lines are caused by vibration/ghosting - the solution for that is to check that all the screws in the frame of the printer are tight and that the belts are tight, and if no obvious cause is found, lower the acceleration and jerk settings. A jerk of 7mm/s and acceleration of 500mm/s will give very good quality (albeit yielding slightly slower printing speeds). A more advanced solution would be to set the slicer to have per-feature accelerations, here are the ones I've settled on for my CR-10 Mini:

image

Hope this helps, let me know how it goes! 🙂

Regards,
Luke

ReplyQuote
Posted : 25/01/2021 7:09 pm
GMRL
 GMRL
(@gmrl)
Member

Hi, Luke!

Thank you very much for your help! I followed your tips for both leadscrew and bearing troubleshooting and it produced a much better print!
However, some lines keep showing:

photo 2021 01 26 18 08 48
photo 2021 01 26 18 08 43

My configurations for this one are:

photo 2021 01 26 18 09 18
photo 2021 01 26 18 09 15
photo 2021 01 26 18 09 12
photo 2021 01 26 18 09 08
photo 2021 01 26 18 09 06
photo 2021 01 26 18 09 00

If you have any other tips, both mechanical or slicer related, please let me know! 🙂
I'll keep testing, printing other models, and I'll send the results. 

Thanks again!

Take care,

Sincerely,
George

Best regards,
George

ReplyQuote
Posted : 26/01/2021 9:52 pm
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi George,

Unfortunately you'll never be able to completely get rid of all horizontal lines because of the lack of precision of the inexpensive leadscrews used in inexpensive printers (my own Cartesian printers have some horizontal lines as well that have been there since the printer's first day) - a precision leadscrew that would be used in something like a CNC machine would alone cost about as much as an Ender 3, so you can understand why they're not included in the kit 😉 . My delta printer doesn't have horizontal lines because the z-axis is belt-driven, but then you get a different kind of circular pattern on the parts from the motion of the diagonal rods.

Having said that, the biggest lines coincide with the top and bottom of the text on the cube, which suggests that we might be able to improve them further by changing a few settings. Here are my recommendations:

  • Horizontal shells - change top to 3, bottom to 3, and minimum shell thickness to 0.6mm top and 0.6mm bottom - this ensures sufficient top and bottom thickness when you go for smaller layer heights
  • Quality - tick "extra perimeters if needed", "avoid crossing perimeters" (and set max detour length to 300%) and "detect bridging perimeters" - these all enhance the print quality by applying optimizations in the scenarios mentioned
  • Fill density - increase to 15%
  • Fill pattern - use adaptive cubic (it saves a lot of filament on big prints because the center of the print has almost no infill; it concentrates the lines near top, bottom and walls, where it's needed most)
  • Extrusion width - set all values to "0" to let the slicer automatically set these (this will come in handy later if you ever decide to change nozzle, because then you can simply change the nozzle size in one box under printer settings, and all the extrusion widths update automatically - no need to edit 8 boxes here by hand)
  • Temperature - I suggest 200 or 210°C - it makes the print shinier, stronger, permits faster printing speeds, and may help hide the lines from the printer's mechanical defects (test it and see how it goes for you - the print quality will decrease a little and overhangs get worse but I personally print all PLA at 210°C because the other advantages outweigh the disadvantages in the majority of cases)
  • Retraction speed - increase to 90mm/s - this will reduce stringing and improve print time. Reduce it again if your extruder gets too noisy or it skips steps
  • Disable wipe while retracting - in most cases the wipe leaves visible defects/lines on your print.
  • Speeds - some of your speeds are a tad too high for best quality, and some can be increased a little bit. I suggest the following (these are also suitable for PETG should you later decide to try it):
image

The basic philosophy is to go fastest on features that you won't see (infill, solid infill) or won't keep (supports), slower on parts that act as a foundation for the parts you see (perimeters, small perimeters, support material interface), and slower still on the parts you see (external perimeters, top solid infill, ironing). Special cases (bridges, gap fill) get slower speeds also for extra reliability.

Hope this helps :). Let me know how it goes!

Regards,
Luke

ReplyQuote
Posted : 27/01/2021 10:59 am
GMRL
 GMRL
(@gmrl)
Member

Hi Luke,

I followed your orientations and I'm obtaining much better prints.
However, some of the lines still remain. I think it may be due to the leadscrew and I'll see about purchasing a new one. 

photo 2021 01 30 19 26 04
photo 2021 01 30 19 25 50

Thanks again for all your help and support! 😀

Take care!

Best regards,
George M.

Best regards,
George

ReplyQuote
Posted : 30/01/2021 10:33 pm
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi George,

That top layer on the last print is beautiful 😀 . Good job getting it dialled in that well! I agree that getting a new leadscrew is the way to go (provided you've double and triple checked the frame and the bearings to make sure they're not the problem). Best way to check the z-bearings and extrusions is to put a soft block of wood or cardboard box, foam or bubble wrap or a plastic stand on your bed to protect it, remove the z leadscrew (being mindful that without the leadscrew the entire gantry will crash into the bed by gravity as there's nothing holding it up, hence the suggestion to use a cardboard box to prop it up at a safe height), then move the gantry up and down by hand gently and feel for bumps or sticking points anywhere in the motion - especially at the bottom where you consistently get those lines. You won't have the motor & leadscrew stopping you so any bumps you feel under these conditions are from the frame. If you don't feel any sticking points or bumps at all - then a new leadscrew is the way to go. If you do feel bumps, look for dirt, damaged or bent rails, or damaged plastic wheels.

One last thing you can try is change layer height to 0.16mm. It will slow down your prints and make the quality improve, but might also shift the appearance of the leadscrew-induced horizontal lines to a way that might look cosmetically slightly better (or won't improve things at all - print one calibration cube and see what happens!)

Looking forward to your feedback 🙂

Regards,
Luke

ReplyQuote
Posted : 30/01/2021 11:49 pm
GMRL
 GMRL
(@gmrl)
Member

Hi, Luke!

Today I disassembled my printer and, following your tips, used a wooden box to support the gantry and managed to fix some parts that were crooked.

I printed another calibration cube, which I stretched to make it taller, and the quality of the print got a lot better (it even fixed some ghosting I had in my prints!).

 

photo4
photo3
photo2
photo1

 

However, the lines still show at the same layers, but not the same height.

I don't know if it really is a leadscrew problem anymore... 🙁

 

Thank you for all the help,

Take care!

Best regards,
George

 

Best regards,
George

ReplyQuote
Posted : 31/01/2021 6:02 pm
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi George,

Previously you were getting lines in parts that had no relation to features of the print - like this one:

image

That's why it was looking like a leadscrew issue. Another significant factor was the fact that the lines were at the same heights on completely different prints.

 

Now the print looks much, much better :). Good job on the overhaul and straightening the crooked bits! The biggest defects I can still observe in your pics are the lines are aligning with the bottom and top of the letters on the cube:

image

That is close to what I would consider acceptable quality for a print (so no need to buy another leadscrew just yet). We might be able to minimize or eliminate them with some further tweaks to the settings.

To do that, can you attach the .gcode file for the tall cube in the picture? Ideally take it straight from the SD card so we can be sure it matches (don't slice another one in case settings have changed since you took the pic). I will re-analyse and see if I can spot avenues for improvement.

What's more concerning are the light defective lines at random heights, but now they look relatively minor so I wouldn't worry about them for now -

image
image

Could you print a simple cylinder of about 20mm diameter and 20-30mm height in vase mode at 0.16mm layer height? You'll find vase mode under Print Settings -> Layers and Perimeters -> Vertical shells -> tick "spiral vase" and click ok.

Vase mode eliminates infill and inner walls and just prints one continuous spiral all the way to the top, with the z-axis constantly moving. The walls should be absolutely defect-free. If you still see irregular layers, your printer still definitely has a residual mechanical problem.

Looking forward to your gcode and the vase mode pics 🙂

Regards,
Luke

ReplyQuote
Posted : 31/01/2021 10:52 pm
GMRL
 GMRL
(@gmrl)
Member

Hi Luke!

I'm happy that you liked the result of my print. It is thanks to you that I accomplished that, I've learnt a lot from you. 😀

Here is the .gcode file for the tall cube:

And here are the pics of the vase mode cylinder, the result is just perfect!
I'm attaching it's .gcode file as well if you want to have a look at it.

cylinder1
cylinder2

As always, thank you for everything! 

Take care!

Best regards,
George 

Best regards,
George

ReplyQuote
Posted : 01/02/2021 11:01 pm
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi George,

That cylinder looks perfect! Your z-axis is now in perfect condition 😀 👍 . Unfortunately we now have to figure out what to fix 😆 .

Here are my recommendations for the slicer:

  • Layer height: 0.16mm
  • First layer height: 0.16mm
  • Untick "ensure vertical shell thickness"
  • Top/bottom solid layers - set to 3 and 3
  • Set seam position to aligned
  • Infill - 15% adaptive cubic
  • Speed - set infill and default acceleration to 1000mm/s2
  • Filament settings - set extrusion multiplier to 0.99
  • Cooling - slow down if layer print time is below - set to 10 seconds

Of all of those, the layer height was the most significant thing making your quality suffer in your cube. With a 0.4mm nozzle, quality really decreases past 0.2mm of layer height (0.25mm max). Yes you can print up to 75% of nozzle diameter (0.3mm in this case) but the process will not be that reliable and quality suffers, especially where there are slight overhangs.

Make a standard 20mm calibration cube with the above settings and we'll take it from there 😀

Regards,
Luke

ReplyQuote
Posted : 02/02/2021 12:36 am
GMRL
 GMRL
(@gmrl)
Member

Hi Luke!

I followed your recommendations and also changed the nozzle from 0.4mm to 0.3mm.
I'm pretty happy with the results! 😍 

cube4
cube3
cube2
cube1

The lines are almost non-existent and really smooth to the touch! 

Thank you very much for all the teachings and tips, and all the help, I really learnt a lot from you!
You're awesome! 😀 

Take care!

Best regards,
George

ReplyQuote
Posted : 03/02/2021 12:05 am
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi George,

Wow, that's a beautiful cube! Glad you enjoyed the process 🙂 . Now onto some more challenging parts! 😀  .

Happy printing! 😀 😀

Regards,
Luke

ReplyQuote
Posted : 03/02/2021 8:48 pm
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