Under and Over Extrusion simultaneously

Hello,
After solving all my printer issues, I have been trying to improve my print quality. But as of now I am stuck and confused what settings needs to be changed. The problem looks like over extrusion from some angle and under extrusion from some angle. Also there are other problems also, which I am not able to understand. Please have a look at the images and help me out. Thanks.

Settings:
Nozzle size: 0.4 mm
Diameter: 1.75 mm
Flow: 70%

Layer height: 0.2
Shell thickness: 0.4
Bottom/top thickness: 0.4
Infill: 15%

Print speed: 50 mm/sec
Printing temp: 190 C
Bed temp: 60 C

Slicer: Cura
Printer: Prusa i3

The 'image 3.jpg' shows what my print usually looks from bottom, its an iphone case in the image.

Too fast for the temperature to begin with, you need to calibrate your nozzle to bed height for first layer, shell thickness cannot be the same as nozzle size (infill is crossing it) usually a 0.4 nozzle extrudes 0.48 so your shell should be minimum at that or 0.96 for better results, top and bottom needs to have more layers, bottom 3 and top 4 to 6. Your flow should be 100% so check your extruder calibration, reduce your jerk XY from 20 to 15 and E from 5 to 4 in the firmware.

Start with that and then come back for more.

@ggherbaz Thank you for the tips. I'll tweak these settings and will revert back. Regarding flow rate, more than 70% extrudes a lot and nozzle starts touching the print after few layers. I guess extruder needs calibration. I'll do that also and will get back.

Agreed, if you are having to set the extrusion to 70% then you are not calibrated at all.

Hello guys, as you guys suggested, I calibrated the extruder, changed from 270 to 100 E-steps(I don't know why I had to do so much). Also changed the flow rate to 100%, Shell thickness to 0.8 mm, top/bottom thickness to 0.6 (no separate setting in cura), Print speed to 40 mm/sec. Now the quality is much much better. Thanks ggherbaz and Floyd. Now there's one problem, the flat sides are having little bumps(See Image1.jpg). I have attached the new print pictures, have a look and please advice me what I can do to avoid those bumps and further improve the quality.

Good that is improving but yet let me explain it again:

Your 0.4 nozzle when extruding the filament makes a line that it's bigger than the nozzle orifice, a normal 0.4 size nozzle extrudes 0.48 if your setting is auto, if manual you can set it to 0.4 but you will face some issues as you are. Those lines you are seeing are the infill crossing the shell, you can see it yourself as it print those lines will match the location where the infill meets the shell. If you still want to print with a 0.8 shell you need to reduce the infill overlap percentage (I use Simplify3d, don't know how to do it with other slicers) if not the best option to prevent that is to increase your shell to a bigger size (I use 3 perimeters as standard, 0.48X3).

Hello ggherbaz,
I increased the shell thickness to 1.2 (0.4 x 3) with speed 40 the print was near perfect, just the layer shifted (Clip 1.jpg). Then I tried 1.44 (0.48 x 3) with speed 50, the quality wasn't good (Clip 2.jpg). Now I am having different problems, I have attached few more images of prints for your reference:
Batarang with Shell 1.2, top/bottom 0.8. Problem: Gaps in top layer
Cable protector with shell 0.8, top/bottom 0.6. Problem: Curves didn't print properly
Pistol (non-working model ) with shell 1.6, top/bottom 1.0. Problem: layer shifting

I am sure I can tweak more to improve the quality. If you can give any advice, that would be great. Thanks.

Edited 1 time(s). Last edit at 07/09/2016 08:20AM by xhm.

Shifting may be caused by several factors:
Under or over powered stepper, loosen belts or pulleys, loosen hotend, etc.

First check and adjust all your stepper motor drivers to the right vref, after that chech all the belts and pulleys for any slack in the belts and loosen lock bolts in the pulleys and then check that your hotend is secured and can't move.

Next calibrate your extruder to the point where when you extrude 100mm your filament moves 100mm in the inlet of the extruder.

Now you need to understand that your printer have some limitations and trying to print beyond 40mm/sec will exceed it, for best quality prints you need to be in the 30mm/sec range just learn to be patient.

One of the most important things you need to learn and practice a lot is to find the best extrusion temperature for the filament you are using, too cold or too hot and the print will show poor quality and then you will have to learn about the extrusion multiplier, too much or too little extrusion and again your print can be ruined or of really poor quality.

But keep going, your prints are really starting to look really good.