2. This angle is the rake angle of the drill. At this time, the wrong angle will directly affect the size of the top angle of the drill bit, the shape of the main cutting edge and the oblique angle of the cross edge. Here refers to the positional relationship between the bit axis and the grinding wheel surface, and 60 is enough, which is generally more accurate. Here, we should pay attention to the relative horizontal position and angular position of the drill bit before grinding, and both should be considered as a whole. Don't ignore the setting angle for balancing the cutting edge, or ignore the balancing cutting edge for setting the angle.
3. 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 first contacts the grinding wheel, and then slowly grinds down along the whole flank. When the drill bit cuts in, you can gently touch the grinding wheel, grind it a little first, and pay attention to the uniformity of sparks, adjust the pressure on your hand in time, and pay attention to the cooling of the drill bit, so as to avoid going too far and causing edge discoloration and annealing. When the cutting edge temperature is found to be high, the drill bit should be cooled in time.
This is a standard drilling and grinding action. The main cutting edge should swing up and down on the grinding wheel, that is, the hand holding the front end of the drill should swing the drill evenly up and down on the surface of the grinding wheel. However, the hand holding the handle should not swing, and the rear handle should also be prevented from tilting upwards, that is, the tail of the drill should not tilt above the horizontal center line of the grinding wheel, otherwise the cutting edge will be dull and unable to cut. This is the most critical step, and whether the drill bit is ground well has a lot to do with it. When grinding is almost the same, start from the cutting edge and gently rub at the back corner to make the back of the cutting edge smoother.
5. After grinding one cutting edge, grind the other cutting edge. The cutting edge must be in the middle of the drill shaft, and the cutting edges on both sides should be symmetrical. An experienced master will look at the symmetry of the drill tip under the light and polish it slowly. The rake angle of the cutting edge of a drill bit is generally 10- 14. The rake angle is large, the cutting edge is too thin, and the vibration is severe when drilling. The orifice is triangular or pentagonal, and the chip is needle-shaped. When the rake angle is small, the axial force is large, it is difficult to cut in, the cutting force is increased, the temperature is increased, the bit is heated seriously, and it is even impossible to drill. The back corner is properly polished, the front tip is centered, and both sides are symmetrical. When drilling a hole, the drill bit can remove chips lightly, without vibration, and the aperture will not become larger.
6. After double-edged grinding, pay attention to grinding the drill tip with larger diameter. After the two edges of the drill are ground, there will be a plane at the tips of the two edges, which will affect the center positioning of the drill. It is necessary to reverse the angle behind the blade and grind the plane of the tip as small as possible. The method is to erect the drill bit, aim at the corner of the grinding wheel, and pour a small groove at the root behind the blade against the tip of the blade. This is also an important point that the drill bit is centered and the cutting is light. Note that when chamfering the edge tip, you must not grind it on the main cutting edge, which will enlarge the rake angle of the main cutting edge and directly affect drilling.
There is no certain formula for sharpening the drill bit, so we need to accumulate experience in actual operation. Only by comparison, observation, trial and error and certain human intuition can we sharpen the drill bit better.