Hollow stemmed stone drill - has helical air supply groove around outside of stem and air entry openings at tip

摘要

The stone drilling tool for e.g. fitting dowels, has a hollow stem (10) through which drilled material can be conveyed upwards from the drilling region and h as air delivery holes (40) through the tip (24). Air is delivered to the tip by a helical channel (12) down the outside of the stem. The tip may consist of a nose piece (32) with a threaded rear part (48) which screws into the end (20) of the hollow stem. The diameter of the stem is smaller than that of the nose piece. The nosepiece incorporates flats (44) or other cut outs for a spanner, forming part of the air supply path. Below the threaded part (48) is a smaller diameter groove (46).