Circular welding of the problem.

My robot R200 İB and controller RJ3. I have a problem with circular welding. I want to pass the Start and end points onto each other and there's nothing wrong about it. But I can't create a kind of full circular shape. The robot also begins to deteriorate as we go further away from the weld shape. Please help me.

Hi robotero,
I don't think hardship related to the calibration of the robot. Any other welding in the study because no problem happens. Round just makes the welding when it is not easy.