How to get a precise hole?

How to get a precise hole?

Firstly get a precise drill bits.

Secondly a stable drill press.

Thirdly stable clamping,include drill clamp and work piece jig.

Drill bits

Bad drill Cutting edge height difference and bad symmetry on the hole diameter，what's the problem?

Problem

First of all, if the edge height difference is bad or symmetry is not good, for the tool is easy to unilateral cutting, that is, an edge is easy to collapse, affecting the life of a tool, and in addition to the parts, it will result in a hole is large, the hole is not round holes are not straight, and the wall of the hole is rough, and the cylindricity of the poor.

Reason

That's the cross blade eccentricity, and cause a single edge cutting, uneven force, lead the cutting surface is not smooth.

How to improve?

Use a tool sharper or get a new better drill bits.