Y axis shifting

Every time I print (if I can get it to) the machine will print 3 layers move on the Y axis about 2mm back and print 3 more and so on it continues to shift at an angle this is very annoying and I continue to lose prints to it. also any suggestions on how to get better quality the prints are terrible almost like the printer doesn't know were to put the next layer. thanks

 

thanks, the belt was really loose cant believe I didn't notice it. but the prints are still very poor quality. I have used the PLA settings for slic3r and repetier. could it be a calibration issue?

 

ok ill try slowing the settings

 

try replacing the washers that attach the bed to the rails. I think the nylon ones were cracked on mine, so I tightened the belt and make sure the screws were at the "closest position" with the belt pulling them together, since the holes are oversized a bit.

 

I had the same issue on X. Turns out the set screws holding the gear on the motor shaft was loose, so it would drift 2-3mm per pass. After I tightened that up, and reattached the belt all was OK.