Why necessary to convert machine from 50hz to 60hz
Most things such as transformers and switching supplies and heaters will run at least as well from 60Hz as from 50Hz, however many motors will run 20% fast and have less torque. 

Solutions include replacing the motors, changing gears or pulleys, rewriting to isolate the sensitive bits and using an inverter or using an inverter to power the entire machine. As an alternative to an inverter, a motor-generator set could be used (a 60Hz generator powered by a 50Hz motor). A VFD (variable frequency drive) is essentially an inverter designed to operate a single motor at variable frequency.

If motors are DC, stepper, servo, already have VFD controls the will probably work fine. The situation is a bit worse going in the other direction as 60 Hz-only motors or transformers may overheat on 50Hz, as well as motors running slow.