Civil Engineering Reference
In-Depth Information
Fig. 11.8. A drill sharpening attachment for an ordinary bench grinder is widely avail-
able at low cost. After a bit of practice it will be easier to sharpen drills with this
device than trying to do it freehand.
Point angles
To drill plastics, the drill point angle could be increased to 90 degrees. If
drilling harder metals, such as steel, which has possibly been heat treated,
the drill can be obtained with point angles of 130, 135 and 140 degrees to
give a longer life to the point.
