The manual sharpening skills of twist drills must be mastered!

The twist drill is a commonly used drilling tool. Although the structure is simple, it is not an easy task to really sharpen it well. The key is to master the methods and skills of sharpening. Once the methods are mastered, the problem will be solved easily. Here I will introduce the manual sharpening skills of twist drills.
The top angle of the twist drill is generally 118°, and it can also be regarded as 120°.

Sharpening drills mainly master several skills:
1. The cutting edge should be level with the grinding wheel surface.
Before grinding the drill bit, the main cutting edge of the drill bit and the grinding wheel surface should be placed on a horizontal plane, that is, to ensure that the entire edge should be ground when the cutting edge contacts the grinding wheel surface. This is the first step in the relative position of the drill bit and the grinding wheel. After the position is set, it is slowly moved to the grinding wheel surface.
2. The axis of the drill bit should be inclined at an angle of 60° to the surface of the grinding wheel.
This angle is the sharp angle of the drill bit. If the angle is wrong at this time, it will directly affect the size of the top angle of the drill bit, the shape of the main cutting edge and the bevel angle of the chisel edge. This refers to the positional relationship between the axis of the drill bit and the surface of the grinding wheel. It is sufficient to take 60°. This angle is generally more accurate. Here, we should pay attention to the relative horizontal position and angular position of the drill bit before sharpening. The two should be taken into account as a whole. Do not ignore the angle in order to level the cutting edge, or ignore the leveling edge for the sake of setting the angle.
3. Grind the back from the cutting edge.
After the cutting edge contacts the grinding wheel, it should be ground from the main cutting edge to the back, that is, the cutting edge of the drill bit will first contact the grinding wheel, and then slowly grind down along the entire flank. When the drill bit is cut in, it can lightly touch the grinding wheel, first perform a small amount of sharpening, and pay attention to observe the uniformity of the spark, adjust the pressure on the hand in time, and also pay attention to the cooling of the drill bit. , and annealed to the edge. When it is found that the temperature of the cutting edge is high, the drill should be cooled in time.
4. The cutting edge of the drill should swing up and down, and the tail of the drill should not be warped.
This is a standard drill grinding action. The main cutting edge should swing up and down on the grinding wheel, that is, the hand holding the front of the drill bit should evenly swing the drill bit up and down on the grinding wheel surface. However, the hand holding the handle cannot swing, and the rear handle should be prevented from rising upward, that is, the tail of the drill should not be raised above the horizontal center line of the grinding wheel, otherwise the cutting edge will be blunt and cannot be cut. This is the most critical step, and whether the drill is well ground or not has a lot to do with it. When the grinding is almost done, start from the edge of the blade and rub it slightly towards the back corner to make the back of the blade smoother.
5. Ensure that the blade tip is aligned with the axis, and the two sides are symmetrical and repaired slowly.
After grinding one edge, grind the other edge. It must be ensured that the edge is in the middle of the axis of the drill bit, and the edges on both sides should be symmetrical. Experienced masters will observe the symmetry of the drill tip with a bright light and slowly grind it. The clearance angle of the cutting edge of the drill is generally 10°-14°. If the clearance angle is large, the cutting edge is too thin, the vibration is severe during drilling, the hole is trilateral or pentagonal, and the chips are needle-shaped; the clearance angle is small, When drilling, the axial force is large, it is not easy to cut, the cutting force increases, the temperature rises, the drill heats up seriously, and even cannot be drilled. The clearance angle is suitable for grinding, the front and tip are centered, and the two edges are symmetrical. When drilling, the drill bit removes chips lightly, without vibration, and the hole diameter will not expand.
6. After the two edges are sharpened, pay attention to sharpening the tip of the drill bit with a larger diameter.
After the two edges of the drill are sharpened, there will be a flat surface at the tip of the two edges, which will affect the center positioning of the drill. It is necessary to chamfer a corner behind the edge to make the flat surface of the edge as small as possible. The method is to stand up the drill bit, align it with the corner of the grinding wheel, and pour a small groove against the tip of the blade at the root behind the blade. This is also an important point for the drill to be centered and cut lightly. Note that when grinding the chamfering of the edge, do not grind it to the main cutting edge, which will make the rake angle of the main cutting edge too large, which will directly affect the drilling.
Of course, there is no certain formula for grinding drill bits. It is necessary to accumulate experience in actual operation. Through comparison, observation, and repeated tests, the drill bits will be sharpened better.