What is wave turning

3D printing problem: wave walls

The problem

When I print with my mElephant 3D printer from Makeblock, the prints come out with corrugated walls as in the picture below. I am using PLA filament from https://makeblock.lt

What i tried

I tried changing the temperatures between 190 and 220 and changing the flow rate. Also check that the screws are not lost. Everything seems fine.

My printer


I had the same problem with ABS, but while printing various test objects, I found that the distance between the wave structures depends on the cross-sectional area of ​​the object. Printing the test cube at 70.1% (1 / sqrt (2) times the original size) takes half the time per layer and the distance between two grooves is doubled. I printed ABS with a layer height of 0.1mm and the simple bang-bang heating bed controller. The temperature fluctuates significantly by 4 ° with a time span of approx. 2.5 minutes, which corresponds to the groove spacing. After switching to a PID controller for the heated bed, the temperature stayed within 0.1 ° C and the problem was gone. Several hundredths of a millimeter of thermal expansion of the heated bed can have significant effects with a layer height of 0.1 mm!

You can enable the PID controller for the heated bed in the Marlin or Skynet firmware by enabling (removing) the following here:

and deactivate (put at the beginning of the line) here:

in Configuration.h. The calibration of the PID controller can then be carried out with the GCODE command:

M303 E-1 S90 C8

for 90 ° C. I had to preheat the heated bed beforehand, otherwise the calibration would time out. The command returns parameters for the PID algorithm. The values ​​can then be applied by the

M304 P579.01 I100.87 D586.0

GCODE command (here for example values). Everything can then be saved in the EEPROM


Bang-bang controller:

PID controller:

Such repeating patterns are usually due to problems in the Z-axis. This is likely caused by bent screws, which in turn cause the X-axis to move. Are the tops of the threaded rods restricted? If so, a simple solution can be to float the top of the threaded rods around by removing the restriction. Most Prusa i3s use a 5mm threaded rod for the screws and an 8mm smooth rod. Does your printer use the same setup?

If your printer has an 8mm (or 5/16 ") threaded rod you can try getting some straight or the better solution would be to get the 5mm threaded rods and just print adapters to accommodate the 5th Keeping the -mm nut in the trap requires new couplings (aluminum or rubber / plastic tubing), 5mm threaded rods, nuts, adapters (printed), and a small change to the firmware. This works as the 5mm - Rod is more flexible than the 8mm smooth rod and is less likely to force the force to wagon around.

If you already have the 5mm threaded rod / 8mm smooth rod I would make sure your X axis is snug and doesn't move on the Z axis smooth rods.

This is easier to highlight when you add a picture of your printer.

To edit:

If your printer is Makeblock's elephant I would try removing the bearings on top that restrict the threaded rods and try printing again.

I have the same problem with a homemade mini extruder. This only happens when the bearing no longer rotates with the extruder gear.

I notice this:

  • The gear collects PLA burrs as it is fed, reducing the traction for feeding the PLA
  • The bearing stops rotating when the pressure is too high or too low.
  • The chamber heat is too high and starts to flatten the PLA before it arrives at the nozzle and has to regulate the speed of the fan. This creates less force when feeding.
  • The PLA has a mix of ABS
  • PLA has partially hardened from boiling over, being extremely dry, etc.
  • The PLA have irregular diameters, for example they are nominally 1.75 mm, but some sections vary 1.8 mm or 1.9 mm
  • The nozzle gets cold due to the direct fan airflow. (maybe your main problem)

:) I've been a quality engineer for plastic and metal processes for 20 years, so I had to analyze why I had a lot of problems, especially in cold weather.

I was considering buying a new extruder like you, but if you have the same problem as me, the extruder is not the problem. You need to check the points described above.

This is the extruder I have, http://aprendiendo.laconeccion.com/mini-extrusor-3dp.

It looks like something is getting caught on the z-axis. A bent piece would likely cause much smaller deformations if it weren't quite obviously bent. Something could be loose and allow for vertical play, maybe the motor mounts.

More likely, in my opinion, is a level difference between the Z-axis worm gears, possibly caused by an obstacle, lack of lubrication, or possibly even improper lubrication. I would look there. Since this is a very consistent pattern, I can assume that your problem can be limited to the top and bottom of the Z-axis worm gears. Even if it's not the problems, I think the problem is most likely up or down.

I once had a very similar problem and the culprit was the relative position of the filament spool and printer. The spool stood on a coaster next to the printer and it turned out that this was enough to put a tensile force on the filament. I put the spool on a shelf above the printer and the problem was resolved.
However, your printer seems to have a much stiffer Z-axis than mine, so the problem here is unlikely.

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