Extruder randomly jams/slips during printing...

hi all.
I have just finished building my Prusa i3.
I have a problem with my extruder randomly jams during the infill.
the first layer onto the bed is always perfect never jams on the first layer.

the jam always happens on the 2nd layer onwards mostly during the infill. I can fix the problem by pushing the filament by hand into the extruder and it resumes printing.
here are some pictures.

It almost feels like the hobbed bolt cant grip the filament hard enough and hence slips.

here are some pictures.
https://www.dropbox.com/sh/dug2fkclcvzchoi/pRrz-rV6eg

like i said it happens randomly and when i push the filament by hand it fixes the problem, until it happens again...

Another question.
I nozzle diameter is 0.4mm what should my layer high be in slicer ? 0.4 ?

Edited 1 time(s). Last edit at 04/20/2014 03:58AM by Haris2887.

mine is jamming to randomly
and i use the same solution
I also want something else as a solution

I think in slic3r you can choose wat suites you
the thing you alter when you alter the layer hight
is just that
it makes smaller hight layers
so that your print is more precize

I drew some things to benefit my printer and you should realy take in consideration making you height and thickness
according to your layerheight ,so if you want a precize peace lets say a cylinder that needs to fit in to something
and the radius of the cylinder is 20 than your layer height should be able to be devidable by 20 so a layer height off 1,2,4,5
are posible butt 3 comes out wrong and the softwere is gonna make a compromise somewhere in the print
at least thats my experiance

any comment please

I've been having the same problem thanks for the suggestion I'll try it out

Do you have any cooling on the upper part of the hotend?

And are you sure it's the right size filament for the hotend, from the zig-zagging fiilament on 20140420_163606.jpg, it looks like the hole in the hotend is too big for the filament.