not extruding enough

Hi there!

I calibrated my extruder and without the hot end it extrudes perfectly. However, when the Hot end is attached, as soon as force is required to push it through the small hole, it starts to get stuck. It travels slowly, but not the intended length. If I extrude manually 10mm from the host it maybe goes only 2mm. You can also see that the hobbed bolt skippes "steps" on the filament. It does look differently when extruded without the hot end.
Where do I have to look for the error? Is it a problem in the hot end? Too cold? How could I verify the temperature? I suspect that the temperature which the thermistor measures is not perfectly correct, but I cant get a good measure with my IR thermometer since the spot is so small.
Or is too less force on the filament? To be honest, I can't imagine the latter, two springs are completely pushed together.

Any hint would be appreciated!

Edited 1 time(s). Last edit at 01/29/2015 06:53AM by GoingForGold.

Did you try to push the filament through the hotend by hand? Does it work?
What filament size and nozzle size do you use? Is it a direct or geared extruder?

Possible Problems could be for example:
- Hotend not hot enough
- Hotend-Cooling area not cool enough leading to jamming

Just to clarify, when calibrating your extruder steps per mm, you are measuring 120mm of filament before it goes through the extruder, not the filament extruder from the hotend.

My guess would be that your hotend is not warm enough, which is creating a lot of back pressure on your extruder, causing the filament to slip and get torn up by the hobbed bolt. Alternatively, you could have a blockage in your hotend, preventing plasitc from extruding.