Why are my circles ovals?

I have a reprappro Mendel and I'm useing pronterface and slic3r and it happens no matter where on the bed I print. Can anyone tell me where to start troubleshooting?

Are they oval in one direction more than the other?

Ovality is normally caused by the steps being of in the x or y direction.

What pulleys?

Ben

If the ovals have flats on them you have backlash in one of your axes.

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Or if they are tilted to one side, the bed doesn't move perpendicular to the x axis.

Edited 1 time(s). Last edit at 05/23/2013 01:30PM by Ralf.

Here's a pic. Hope it you can see it.

Another pic

Thats a clear case of backlash. Whats happening is that the motor reverses and moves a fraction before the mechanism starts to move in the other direction.

Make sure that your belts are decently tensioned and that there is no play in the system. Make sure the drive pulleys are firlmy attached to the motor shaft, make sure that the belt isn't slipping at the clamp. If all else fails, the slicer can compensate for backlash to a degree but for best results you want to get the machine as close to perfect as possible, and use backlash compensation as little as possible if at all.

Are your squares square?

Tightened up the belt and works much better! Thanks guys