Twist drill is a commonly used drilling tool. Although the structure is simple, it is not an easy task to sharpen it. The key is to master the methods and techniques of sharpening. Once the method is mastered, the problem will be solved. Here is a brief introduction to the manual sharpening technique for twist drills.
The apex angle of the twist drill is generally 118°, and it can also be regarded as 120°. There are several techniques for sharpening the drill bit:
1. The cutting edge should be level with the grinding wheel surface.
Before grinding the drill bit, first place the main cutting edge of the drill bit and the grinding wheel surface on a horizontal surface. That is to say, when the cutting edge contacts the grinding wheel surface, the entire cutting edge should be ground. This is the first step in the relative position of the drill bit and the grinding wheel. Position it and then slowly lean against the surface of the grinding wheel.
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 front angle of the drill bit. At this time, the angle is wrong, which will directly affect the size of the top angle of the drill bit and the shape of the main cutting edge and the bevel angle of the transverse edge. Here is the positional relationship between the spindle axis and the surface of the grinding wheel. Take 60°. This angle is generally more accurate. Here, we must pay attention to the relative horizontal position and angular position of the drill before sharpening. The two should be balanced. Do not neglect the angle of the pendulum to flatten the edge, or ignore the flat edge for the angle.
3. Grind the back from the edge of the blade.
After the cutting edge contacts the grinding wheel, it is ground from the main cutting edge to the back, that is, the grinding wheel is first contacted from the cutting edge of the drill bit, and then slowly milled down along the entire flank. When cutting the bit, you can gently touch the grinding wheel, first carry out a small amount of sharpening, and pay attention to observe the uniformity of the spark, adjust the pressure of the hand in time, and pay attention to the cooling of the drill bit, so that it can not be over-fired, causing discoloration of the cutting edge. And to the edge of the annealing. When the cutting edge temperature is high, it is necessary to cool the drill bit in time.
4. The cutting edge of the drill should be oscillated up and down, and the tail of the drill cannot be lifted.
This is a standard bit grinding action. The main cutting edge is swung 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. The hand of the grip can not swing, but also prevent the back handle from being upturned, that is, the tail of the drill bit cannot 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 the drill bit is good and bad, which has a lot to do with it. When grinding is almost the same, start from the cutting edge and gently rub the back corner to make the back of the blade smoother.
5, to ensure that the blade tip is on the axis, and the two sides are symmetrically repaired slowly.
After one edge is ground, and the other edge is ground again, the edge must be in the middle of the bit axis, and the edges on both sides should be symmetrical. The experienced master will look at the symmetry of the drill tip and slowly grind it. The back angle of the cutting edge of the drill is generally 10°-14°, the back angle is large, the cutting edge is too thin, the vibration is severe during drilling, the orifice is three-sided or pentagonal, the chips are needle-shaped; the back angle is small, The axial force during drilling is very large, it is not easy to cut in, the cutting force is increased, the temperature rise is large, the bit heat is severe, and even the drilling cannot be performed. The angle of the back angle is suitable for the centering, the two edges are symmetrical. When drilling, the drill bit is light, no vibration, and the aperture will not expand.
6. After the two edges are ground, the drill bit with a larger diameter should also be sharpened.
After the two edges of the drill bit are ground, there will be a plane at the edge of the two edges, which affects the center positioning of the drill bit. It is necessary to pour the corner behind the blade and make the plane of the tip tip as small as possible. The method is to erect the drill bit and align it with the angle of the grinding wheel. At the root behind the blade, pour a small groove against the edge of the blade. This is also an important point in the centering of the drill bit and the brisk cutting. Note that when chamfering the edge of the sharpening edge, it must not be ground to the main cutting edge, which will make the front corner of the main cutting edge larger, which directly affects the drilling.
Of course, the grinding bit does not have a certain formula, and it is necessary to accumulate experience in actual operation. By comparing, observing, and repeatedly testing, the bit will be ground better.
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