Rahni:
I have designed flying cutoff for pipes in the past, the basic idea is that carriage reaches pipe mill speed before cutting. So PID is used to make carriage accelerate and mantain same speed as pipe mill, then carriage clamps against the pipe until cutting is finished, then go back home until next cut.
Encoder located on pipe mill must be as a high ppr as possible and quadrature, the same for encoder located on carriage.
Please take into account that servo board max frequency should be greater than the one produced by encoders when moving.