Thread: Hand-sharpening of drill bits

Wouldn't the angle between the nuts be 120° which is close to the general 118°

AS far as whether to be exact with angles or not, for me I make that decision at the time of sharpening based on what I am doing, if I am drilling lots of holes in mild steel with a small size, say 3mm to 10mm and using the hand power drill I'll just sharpen by eye, I will look at it to try to maintain symmetry and this is the important point in sharpening any multi edged cutting tool, the drill bit performs best when both (or multiple) cutting edges are cutting equally, this can be seen as evidenced by the shape (and sound) of chips coming out of the hole, two corkscrew shaped bits of swarf should be the result in mild steel, if only one or it's a different shape or thinner or........... you know it's not symmetrical, so if your drill bit is cutting OK and removing metal go with that and it's not critical whether it's at 120° or 119° or 121° or 118°, if however I am using the radial arm drill with larger bits I usually will sharpen to the 118° as per my guages to get the symmetry and the longest working life of the cutting edge, cutting angles are a function of cutting edge life, mat'l removal rate (swarf), mat'l being cut, safety, machine capability, quality of hole shape/finish produced, a clean smooth round hole can be cut in sheet metal using a completely different shaped drill bit to the normal 118° but would not last any time if it were to be used trying to drill 1/2 thick bit of steel, the normal 118° dril bit will drill a hole in sheet metal but the hole produced will be a rougher/ragged shaped hole.

The aim certainly is to produce correct cutting edge angles with the correct clearances and should be the target but in general 119 will cut as well as 118.
To get a feel for the action required at the wheel a good trick to start with is present a new (or correctly sharpened) larger diameter drill bit on a stationary wheel and try to follow the angle/shape already on the drill bit by holding the bit with two fingers (right hand) at the 118° while rotating the wrist (left hand) which produces the clearance angle behind the cutting edge, if you get these two in the park it will cut, next to consider is the web to cutting edge angle, web thinning, using a stone to radius the sharp outer edge corner but that is down the track.


Pete