If you wanna get your pipes and axis concentric accurately, the followings need to be assured.

1. High enough installation accuracy of your chuck( Always a machine is set well including centering, but its precision will be low increasingly.)
2. Calibrationof B axis center( A rectangle pipe is necessary）
3. Standard pipe to be cut.( For example, a rectangle pipe of 40×40, but actually it is 40×41, some errors may occur while cutting)
4. Centering at periodic intervals or every few parts( You can enable Centering in Processing to assure your pipe is always on the right place.)
5. Same size of your drawings and your actual pipe, including length, width, thickness, chamfer etc.

      Now some deviation occurs, it is kind of hard to tell which step goes wrong.

      But all five points above need to be assured if you want your machine to work accurately. In general, adjusting the chuck, re-calibrating B axis and enabling Pro-center (Centering before processing) can get the deviation problem solved.

      To be simple, you’d better have a try one by one starting from the easiest one, checking if your drawings are exactly same to your pipes, if they do, add some Centering Points in Processing. But        if that doesn’t work, calibrate B axis center and have a try; But if all the operations above still don’t work, you have to adjust the chuck.