The drill bit angle is at the tip of the bit, and it seriously affects how well the bit cuts various materials The consumer drill bits commonly use three angles: 90°, 118°, and 135°. There is no strict standard for the drill bit angle, so the good choice depends on the work.
The 118-degree bit cuts aggressive and is used for drilling in soft materials as wood until aluminum. It can penetrate steel, but the sharp angle dulls it quickly. Historically you considered 118° the best, and many yet favor it.
How to Choose the Right Drill Bit Angle
A sharper peak starts easily, but wears out more soon.
For hard materials as steel, stainless steel or cast iron, the 135-degree angle is better. Its flat peak spreads the pressure, which reduces wear and gives smooth holes. At hard materials it lowers cutting forces.
Flatter points hardly start, but live more long. Almost always it has a split peak, that stops skating on the surfcae.
The geometry of the peak controls skating, when the bit slips or wanders before the slice. Usually for more hard material you use a shallower angle, around 140° or more. A narrow drill bit angle leaves web residues above the sharp edge.
The sharpening angles relate to those between the sharp edges and the axis of the drill bit. Between them are the helix angle, that affects curling of the chips, the lip clearance angle for relief of the edge, the cutting angle between lips and the chisel edge angle between lip and chisel edge. The lip angle is 12°.
Well sharpened chisel edges must be straight.
Before drilling the spot drill angle should surpass that of the drill bit. For 118-degree drills a 120-degree spot drill works. At 135-degree drills you favor a 140-degree spot drill.
The drill should first cut the center, not the location of the edge.
Drilling in quarter-inch angle iron, first do a pilot hole of 1/8 or 3/16 inch to stop burning out of bits. Cutting oil or cutting wax also help. Well understand clearance and rake angles give good results; check the tip to see if the sides are equal, that quickly shows whether everything is well sharpened.
