CNC machining parts surface from different factory

Why the products surface is different from different factory ?

some rough (have many milling line ), some looks very smooth (a few lines or no milling lines). Why ?

in fact , some factory will make polishing after cnc machining , but some factory dont do the work . so if have polishing , the surface will good .

When you choose a factory , mabye you can ask them how to do it .

AIXI RAPID