Very bad lateral surface - need help

[SteffenS]

Hello there,
at first sorry for my bad english!
I have a Prusa i3 Steel with MK8 Direct Drive extruder, Nema 17 motors 1.2A, RAMPS 1.4 Board with Marlin firmware.
In the beginning I had problems with small waves on the lateral surface. Then I swapped the cheap China LM8UU bearing against IGUS RJ4JP. On the X and Y axis.
It was slightly better, but still not good.
Then I swapped all the motor drivers from A4988 to TMC2100. Also for the extruder.
Nevertheless, I have no nice surface finish. The surface seems somehow "turbulent". It looks like small micro waves, but they do not feel with your finger.
The belt I have rotated on the idler side so that the smooth surface runs on ball bearings. Also does not help.
Look at the pictures, please. You can see what I mean. The small cube is printed with 0.2mm layer height, the great with 0.3mm.
Maybe you have a tip for me?

My hard and software:
Prusa i3 Steel
MK8 dd extruder
0,4mm Nozzle
1,75mm PETG from Extrudr.eu
230°C nozzle
93°C bed with PEI plate
Nema 17 1,2A motors
RAMPS 1.4
Marlin
Slic3r

Speed Perimeter: 35mm/s
Speed extern Perimeter: 70%
Speed Infill: 40mm/s


Best regards from germany
Steffen

IMG_6463.jpgIMG_6464.jpgIMG_6459.jpgIMG_6460.jpgIMG_6461.jpg

[ServiceXp]

Doesn't look bad to me for .2 resolution.

[Sebastian Finke]

If you mean the ripples near the corners that's called corner ringing and it has to do with the extruder changing direction and the steppers trying to rectify the over/under shoot. This can be almost entirely cancelled out by:

- turning on acceleration
- modifying acceleration parameters
- slowing down print speed
- decreasing moving mass (eg. removing second extruder if dual)

This is a basic physics issue. Nothing wrong with the LM8UU bearings.

[LambdaFF]

What Sebastian said. Alternatively, add a chamfer on the corner : it will help too because you won't have such sharp accelerations/decelerations.