Basic Drilling

Hole positional accuracy is the accuracy that refers to the deviation allowed from the required hole position. For example if the hole positional accuracy is 0.1mm then as long as the drilled hole is within a 0.05mm range from the desired location it is OK. If it falls outside of that then it will be out of tolerance.

When using a long drill or a drill with S thinning, it is difficult to achieve high hole positional accuracy. Therefore prior to drilling it is recommended to use a stub drill to open the hole and then follow on with the long drill.