31
THE CORRECT USEOF CENTRE DRILLS
A guide to successful drilling
Recommended Speeds
The peripheral speeds for centre drills are the same as for 2 flute
drills given on page 10-11. For calculation purposes the nominal
diameter given below should be used.
Centre Drill
Nominal Centre Drill
Nominal
Size Diameter (mm) Size (mm) Diameter (mm)
BS 1
2 1
2
BS 2
3 1.25
2
BS 3
4 1.6
3
BS 4
6 2
4
BS 5
8 2.5
5
BS 6
11 3.15
6
BS 7
14 4
7
5
9
6.3
11
8
14
10
18
Recommended Feeds
Use the nominal diameter given above to establish the feed as given
on page 19, and then reduce by 40% for centre drills.
Re-sharpening of Centre Drills
Centre Drill can be re-sharpened on the point only. refer to the
re-sharpening guide for 2 flute drill on page 24/25.
