Civil Engineering Reference
In-Depth Information
Fig. 11.6. Engraving cutters are made with many different cutting shapes. Something
like this makes an excellent centre drill.
DIFFERENT TYPES OF DRILL
Twist drill
Until recently, the standard twist drill had not changed from when it was in-
vented back in the early 1860s. The twist drill has spiral flutes and a standard
inclusive angle of 118 degrees to the point.
Four-facet drill point
Recent advances in technology have seen the introduction of the four-facet
drill point. This makes the drill self-centring, especially in the shorter or stub
sizes. The four-facet point tends to cut better than a standard twist drill point.
It is also far easier to sharpen by hand in the home workshop, although ideally
a drill sharpening jig should be used.
