(1) One is to bore perpendicularly to the surface.

A good way to do this is to lay the work flat, either on the bench or in the vise, and sight first from the front and then from the side of the work, to see that the bit is perpendicular both ways.

The test may also be made with the try-square, Fig.

137, or with a plumb-line, either by the worker, or in difficult pieces, by a fellow worker.

The sense of perpendicularity, however, should constantly be cultivated.