Printer problems

Hello,

Can someon give me his opinion what the cause is that my print moves sometimes. What i mean is that it prints a couple of layers and then the hole print is moved 5 mm or so.

Also what modifications can i do to my prusa mendel to have a flat print?

If you look at the picture you can see that the walls are not perfectly flat.

Charlie

I looked at your picture and it's showing your extruder....

A few things that can cause various amounts of shifting(lost steps)
-stepper drives are not adjusted properly. (need to increase current going to the motors)
-Firmware or print speeds are too high for your machine.(try lower print speeds)
-Belts are too tight
-Damaged belts(metal reinforcement/bands in the belts are broken)
-Motors are underdriven