Drill bit sharpening principles

With correct use and sharpening, the optimum durability of our drill bits can be achieved, thus reducing your tool expenditures. Drill bit sharpening is a precise operation requiring a dedicated sharpener, correct tools and equipment, and highly-skilled personnel. Drill bits should be frequently sharpened to prevent excessive or even catastrophic damage of the blades, which could result in the drill bit breaking.

The following criteria indicate bluntness of a drill bit:

  • reduced smoothness of the drilled hole surfaces,
  • significant increase of the machining temperature,
  • chip discoloring,
  • exceeded hole diameter tolerance or hole deformation,
  • the occurrence of an acoustic criterion for bluntness, i.e. excessive noise,
  • the occurrence of physical symptoms of bluntness in the form of a narrow triangle by the chisel edge on the flank and stripes on the land in the flutes.

Exceeding an acceptable level of bluntness can lead to the chipping of the chisel edge or its breaking off. In extreme cases, the bit may simply break.

Before proceeding to sharpen, carry out a visual inspection of the blunt bit, and then remove all fissures, chippings and cracks from the chisel edges. Maintain the symmetry of the chisel edges, aiming at restoring their factory shape.

Drill bits are correctly sharpened when procedures are conducted with the correct sharpening and cooling parameters, so as not to cause excessive heating of the chisel edge areas. An excessive temperature increase in the course of sharpening can cause grinding fissures, microcracks, high edge tempering or even their secondary hardening. These negative phenomena deteriorate the quality and performance of drill bits. The higher the alloy content of high-speed steel used to manufacture a drill bit, the more precise the sharpening process should be. The sharpening of bits made of tungsten-molybdenum steel should be carried out at 20-25 m/s, and the stroke should not exceed 0.03 mm with manual shift. Sharpening tools made of SK8M cobalt high-speed steel requires a 25% reduction of all parameters or the use of Borazon (boron nitride) grinding wheels.