The Cutting Edge Must Be Aligned Flush with the Grinding Wheel Surface.
Before sharpening a drill bit, you must first position the bit's main cutting edge on the same horizontal plane as the grinding wheel surface. In other words, ensure that when the cutting edge makes contact with the wheel, the entire length of the edge is being ground. This constitutes the first step in establishing the relative positioning between the drill bit and the grinding wheel; once this alignment is set, you can slowly bring the bit into contact with the wheel surface.
The Drill Bit Axis Must Be Angled at 60° Relative to the Grinding Wheel Surface.
This angle corresponds to the drill bit's point angle. If this angle is incorrect at this stage, it will directly affect the size of the drill's point angle, the geometry of the main cutting edges, and the angle of the chisel edge. Specifically, this refers to the positional relationship between the drill bit's central axis and the surface of the grinding wheel; a 60° angle is the standard requirement, and it is an angle that is generally easy to judge visually. It is crucial to pay equal attention to both the horizontal alignment and the angular positioning of the drill bit prior to grinding; do not neglect the angle setting while attempting to align the cutting edge flush, nor neglect the edge alignment while attempting to set the correct angle.
Grind the Flank (Relief Surface) Working Backwards from the Cutting Edge.
Once the cutting edge makes contact with the grinding wheel, you must grind the surface immediately behind the main cutting edge-known as the flank or relief surface. This means the cutting edge itself should be the first part of the drill bit to touch the wheel, followed by a slow, sweeping motion along the entire relief surface. When engaging the wheel, apply only light pressure initially to perform a minimal amount of grinding. Observe the uniformity of the sparks being generated and adjust your hand pressure accordingly in real-time. Additionally, pay close attention to cooling the drill bit; do not allow it to overheat, as excessive heat can cause discoloration of the cutting edge and lead to annealing (softening) of the metal. If you notice the cutting edge becoming excessively hot, cool the drill bit immediately.
The Drill Bit's Cutting Edge Must Be Rocked Up and Down, While the Tail End Must Not Lift Up.
This describes the standard motion for grinding a drill bit: the main cutting edge must be rocked in an up-and-down motion against the grinding wheel. Specifically, the hand holding the front section of the drill bit should execute a smooth, uniform rocking motion across the wheel surface. Conversely, the hand holding the shank (handle) section must remain steady and prevent the tail end of the drill bit from lifting upward. That is, the tail of the drill bit must not rise above the horizontal centerline of the grinding wheel; doing so would result in a dull cutting edge incapable of performing any cutting action. This is the most critical step in the process; the ultimate quality of the sharpened drill bit depends heavily on the correct execution of this specific motion. Once the grinding is nearly complete, begin at the cutting edge and gently brush back toward the relief angle to ensure the surface behind the edge is as smooth as possible.
Ensure that the drill point remains aligned with the central axis, and proceed slowly to refine the shape while maintaining symmetry on both sides.
Once one cutting edge has been properly ground, proceed to grind the other. It is imperative to ensure that the cutting edges are centered precisely on the drill's axis and that both edges are symmetrical. Experienced craftsmen will hold the drill tip up to a light source to visually inspect its symmetry, making gradual adjustments as they grind. The relief angle (clearance angle) for a drill bit's cutting edge typically ranges from 10° to 14°. If the relief angle is too large, the cutting edge becomes excessively thin; this leads to severe vibration during drilling, results in a triangular or pentagonal hole opening, and produces needle-like chips. Conversely, if the relief angle is too small, the axial thrust force required for drilling becomes very high; the bit struggles to penetrate the material, cutting forces increase, and significant heat is generated-potentially causing the drill bit to overheat severely or even rendering it incapable of cutting at all. When the relief angle is ground to the appropriate specification-with the drill point centered and both cutting edges symmetrical-the drill will evacuate chips smoothly and without vibration during operation, and the diameter of the drilled hole will remain accurate without enlargement.
Once both cutting edges have been successfully ground, particular attention should be paid to refining the drill point itself, especially when working with larger-diameter drill bits.
