Hello all! My name is Niels and i am a 3d printer newbie. I have watched tons of guides and tutorials on 3d printing. I suppose I spent around 20-30 hours doing that while building my printer. I do have some electronics skills and i am sort of handy as well, so i figured i should be able to construct a functional 3d printer. (Heck, i made my own WiFi-controlled LED plant grow light, with adaptive spectrum!)

I have a problem i can not seem to figure out and i can not really find on the internet. I did have a few other problems which i managed to solve on my own, including filament stripping, underextrusion and not perfectly level X-axis (Horrible noise).

My setup:
Prusa i3 - Steel, 12V, NEMA17, igus-drylin bearings, Ramps 1.4SB, DRV8825 drivers
Wade-style extruder, E3D V6 all-metal hotend (1.75mm), Mk3 aluminium heatbed. 0.3mm nozzle

Problem:
I am trying to print my PLA at the reccomended temperature of 220C on painters masking tape (yellow, cheap). The heatbed is at 50C (Worked better for adhesion than 60C). The print itself is a single walled upright bar, with bottom, no top. Layer height 0.2mm, speed 50 mm/s.

I observe gaps in extrusion, as shown in the picture. I see a nice steady stream of plastic flowing from the nozzle, and then suddenly nothing, and a little later it just continues. (In bad cases, when it continues it curls up at the nozzle and makes a mess, dragging everything along).

Diagnostics performed:
Simple extrusion through hotend in pronterface - 10 mm @ 100 mm/s occassionally hear a popping sound and see an irregularity (bump and decrease of flow) in the plastic stream, when extruding @ 10mm/s this becomes more pronounced.
Simple extrusion without hotend in pronterface - 100 mm @ 100 mm/s, perfectly extrudes 100mm of filament. (I did have to add about 20% steps/mm in Marlin to ~1950)

Tests:
Tried temperatures between 200-230 - No real difference
Tried extrusion multiplier between 100-110 - No real difference
Cleaned the barrel and nozzle very thoroughly with chloroform twice (Dissolves PLA) and used a toothbrush inbetween the two treatments. - No difference
Cleaned the hobbeld bolt with a toothpick and compressed air (was some slight grindings from skipping extruder from before) - No difference

I believe after spending about 10 hours on failed prints and searching for solutions on the net, i can say i honestly dont know what i could do more. (Except for maybe a extra extrusion test WITH hotend, although i did calibrate the extruder with the hotend before.)

Personally i suspect filament flexing/bending or snagging in the hotend barrel, getting softer/melted after a little while and releasing the pressure allowing for further extrusion. But as far as i know this should not happen.

Regards,
Niels

PS: I have the same question on a different forum, but i later thought this forum might be more appropriate.