When to use pilot hole before drilling Practical Machinist
2018 9 15 nbsp 0183 32 And once a starter hole is established a larger drill will follow it fairly faithfully Thus a 1 2 quot drill will certainly start a hole withing 1 4 quot of the marked or punched location But for many purposes that is just too much slop Now if I start that hole with a 1 8 quot drill then it will be centered to within 1 16 quot and that is a lot better