Feeding problem?

I'm bussy trying to calibrate my Prusa for a while already. And mannaged to eleminate several problems already. For smaller prints, quality seems to be ok. But for bigger prints I'm not sattisfied.
Seems I have some kind of feeding problem. On bigger prints the infil seems to miss lines randomly or are verry thin. And it seems that parts of vertical layers missing randomly.

I've already:
- adjusted the current to the extruder.
- tried diffrent extruder springs with diffrent length and tensions.
- adjusted the retration length.
- adjusted the speed.
- adjusted the extruder feeding rate (feeds approxametely 10cm when feeding 10cm manually)

Anny help or tips are welcome!








Edited 1 time(s). Last edit at 04/23/2015 08:12PM by Rockel83.

It's some while ago since I've posted about this problem. Got verry tired of it, so I didn't have used my printer for a while now.

Recently tried to looked over the problem again. It seems this was a case of under extrusion, and that the extruder kept skipping steps. Even when I've turned up the current on the controller board to it's maximum. Couldn't solve the problem by changing settings in Slicer or EEPROM, so I thought it had to be a physical problem.
I've measured the voltage to the extruder, which was about 3,5V to 4V, while the extruder motor has a nominal voltage of 2,7V. So the stepper motor should not deliver enough torque to squeeze out the molten filament. So I've replaced the extruder motor with another one with a higher nominal voltage and slightly more torque, and the problem was gone

Interesting one!

More usual causes of this problem are inadequate tension on the springs, badly cut hobbed bolt, low printing temperature (for large prints, fast infill, there is increased flow in the extruder and it is harder to heat up the passing plastic adequately), and, if you have a geared system, small gear slipping from the motor shaft (for large prints the extruder motor can get hot and heats up the gear which can then get slack)

Edited 2 time(s). Last edit at 08/24/2015 07:42PM by fixerT.

Thanks for your input!
I've tried a lot of different things to fix this problem before. Tried different settings in the EEPROM and in Slicer without anny result, tried different temperatures between 180 to 220 degrees for PLA. And even tried different springs with different tensions (direct extruder). But all without results.

I was looking for a solution to minimize the pressure in the hot end, because of the skipping extruder. But nothing seemed to help.

Should have checked and compared the voltages of the extruder motor much earlier. It should have saved me a lot of annoying moments

Hope this can help others.