Can't get my PLA printing right.... HELP!

[trimmedup]

Hi guys, can't seem to get my 3D printer to print in PLA correctly. No problem with ABS at all.

I'm using an aluminum platform, heated to 50c with my extruder at 190c. Whenever I print, it seems as though the layers start bunching up on my extruder. The extruder seems to hit the previous layer, but if I raise the nozzle up, the print quality is horrible. Any ideas?

[CaptainObvious]

Are you using a cooling fan? A heated bed is not really necessary for PLA.

[jimc]

how about some pictures? if your nozzle is dragging on the layer as it moves around then that a good sign of over-extrusion. too much plastic is being pumped out.

[CaptainObvious]

Ah, yes, there's that too. You should make sure your ABS filament is the same diameter as your PLA filament, it may be that your PLA is thicker.

[trimmedup]

I'll try and get a photo. I threw out my last print and kinda just stopped using my printed, I've become so discouraged.

To answer the questions. Yes, I am using a cooling fan. I am also using a heated bed, but also tried with painters tape (plus heated bed - 50c)

What causes over extrusion? My PLA isn't any thicker than the ABS. They are identical.