the drill will follow the existing hole, right?

Was more concern about the hardness of the pinion than getting it 110% straight, guess i just gonna give it a try. dont have an drill press, and dont want to bug other to help me

if i sand the shaft down from 6mm to 5mm, i think there will be more risk about getting it straight than drilling the pinion. atleast its better to risk a pion than the shaft.