I am an old newcomer to engineering workshop practice and I don’t suppose I shall live long enough to learn to sharpen twist drills properly freehand. I have made many attempts and I sometimes succeed in getting a drill which cuts true and to size, but what I want is consistency. Many devices have been studied and tried for grinding the clearance correctly, but I can’t make most of them produce an accurate drill repeatedly.
As all proper engineers know, the first essential is to have two cutting edges of equal length and at the same angle to the axis of the drill. The second is to have the clearance equal on each side and the third is to be able to change angles and clearances for different materials. Provided that the drill can be offered to the grindstone at a predetermined angle, it should not be difficult to obtain a consistently good drill. I therefore turned my thoughts to a jig to make this possible, and at the same time I chanced upon articles by D. A. G. Brown on four facet drill sharpening (ModeI Engineer Vol. 172 Nos. 3690 and 3692). His jig makes it almost impossible not to grind a drill properly, but it is confined to small drills up to about 3mm. I wanted to sharpen larger drills to the same high standard, and ER20 spring collets provided the next answer when I was told that they will hold a drill accurately by the lands. They have the advantage that each collet has a holding range of 1mm, so all drills from 3mm to 13mm, metric or Imperial can be held in relatively few of them.
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From the Archives: Twist drill Sharpening by the Four Facet Method
Giles Parkes, MEW Issue 64, February/March 2000
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