Some time ago I have written about my RepRap clogging problem. When I have switched to PLA I had some problems with extruder jams. It was solved by switching to different extruder and adding a fan for active cooling.
As it usually is when you solve one problem an another one emerges. This situation is nothing less. When the extruder finally started to work properly I had some issues with Y axis. Below you can see a few photos which emphasise the problem. The reason of the bad print out was quite simple. The stepper motor was loosing steps. The reason behind it was of a mechanical nature rather than of an electronic one.
The belt was not tense enough. I decided to change the belt and also make some slight modifications to the heating bed. After changing the belt which by the way was a bit worn out everything works like charm.
Here you can see the difference between good printout and a bad one. There is a visible offset and the quality is really bad.
Now it is a time to make some nice printouts. Soon you will find out what it is.