tralalas:
I need to get that cut ranging from 50 to 51mm.
I presume you mean 50.5mm +/- 0.5mm
If I would use 1.8degree Stepper motor what do you think the accuracy of its cut will be, using the tools indicated in the video.
The stepper will be fine (possibly with microstepping). Its the equipment attached to it that you need to experiment with. For example there may be slippage between your material and the rotating wheels. That sort of thing won't be in any datasheet.
...R