The principle applies also at the exit side of the drilled hole, even though it is not as critical as the entrance side. While (b) Is preferable to (a), both entrance and exit need to be "perpendicular design's", as in (c) and (d).

To avoid interference with the drill exit, such as in (a), arrange holes at a safe distance from other portions of the workpiece (b).

Blind holes with square ends are expensive. Best and least expensive design is to bottom with a taper corresponding to the 118º angle of a standard drill (b). If a square end cannot be avoided, include as much of the taper as possible (c), or better still, add a small-diameter bore (d). If a dowel pin is to fit in the main bore, design (d) is necessary in order to be able to remove the pin, if needed, and to avoid trapped air, which may impede assembly.

Tapered reamers should not work against shoulders (a), as this requires special tooling and more maintenance. Change to design (b), if possible.

When drilled holes intersect, the drill deflects when the second hole is drilled. The distance, "1", between the axes of the holes should be sufficient, as in (b), for the following procedure: first, hole "d is finish drilled; then the second hole is predrilled with diameter d1 finally diameter d1 is in. creased to d2 using a counterbore with a guided pilot of diameter d1. If the distance `1' is too short, as In (a), hole "d" would have to be filled with a tight plug (of the same material as the workpiece), which is removed after completion of the drilling.