A twist drill is a commonly used drilling tool, the structure is simple, to grind the bit edge is very important for the workpiece processing. But to grind it really good, is not an easy thing. The key is to master the method and skills of good edge grinding, the method to master, plus many times the experience of edge grinding can be a good master of the edge grinding scale of the drill.
The top Angle of twist drill is generally 118°, but it can also be regarded as 120°. Sharpening bit can master the following 6 skills generally there is no problem.
1. Before grinding the drill, the main cutting edge of the drill should be placed on a horizontal surface with the grinding wheel face. That is to say, when the cutting edge touches the grinding wheel face, the whole edge should be polished. This is the first step of the position of the drill bit relative to the grinding wheel.
2. This Angle is the tip Angle of the bit. If the Angle is wrong, it will directly affect the size of the bit tip Angle, the shape of the main cutting edge and the Angle of the transverse edge. This refers to the position relation between the axis of the bit and the surface of the grinding wheel. It is ok to take 60°. The two should be taken into consideration as a whole, and the degree Angle should not be neglected in order to balance the edge, or the edge should be neglected in order to balance the edge.
3. After the cutting edge contacts the grinding wheel, it shall be ground from the main cutting edge to the back. That is, it shall first contact the grinding wheel from the cutting edge of the drill, and then grind down slowly along the whole back cutting surface. When the drill bit is cut in, it can touch the grinding wheel gently. Firstly, it needs to grind a small amount of the edge, 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. So that it cannot be overheated and cause the cutting edge to change color, and then the cutting edge can be annealed. When the cutting edge temperature is high, cool the drill in time.
4. This is a standard drill grinding operation. The main cutting edge should swing up and down on the grinding wheel. However, the hand holding the handle cannot swing, and the rear handle should be prevented from turning up. That is, the tail of the bit should not turn up above the horizontal centerline of the grinding wheel, otherwise, the cutting edge will be blunt and cannot be cut. This is the most important step, and it has a lot to do with how well the drill is ground or not. When the blade is almost polished, it should start from the edge and gently rub against the back corner to make the back of the edge smoother.
5. After grinding the edge on one side, grinding the edge on the other side must ensure that the edge is in the middle of the drill axis, and both edges should be symmetrical. An experienced master will look into the bright light to see the symmetry of the drill tip and slowly grind it. The back Angle of the cutting edge of the bit is generally 10°-14°. The back Angle is too large, the cutting edge is too thin, and the vibration is severe during drilling. After the Angle is small, drilling when the axial force is very big, not easy to cut in, cutting force increases, the temperature rises, the bit heating is serious, even unable to drill. The rear Angle is suitable for Angle grinding, the front point is in the center, the two edges are symmetrical, when drilling, the bit chip discharge is light, no vibration, the aperture will not expand.
6. After the two cutting edges are sharpened, it is necessary to sharpen the tip of the drill bit with a larger diameter.
After the two edges of the drill are sharpened, there will be a plane at the tip of the two edges, which will affect the center positioning of the drill. It is necessary to reverse the Angle at the back of the edge and make the plane of the tip as small as possible. The method is to hold the drill bit upright, aim at the Angle of the grinding wheel, at the root of the back of the blade, and make a small groove towards the edge. This is also an important point for the bit to center and cut lightly. Note that when trimming the edge chamfering, never grind to the main cutting edge, this will make the main cutting edge of the front Angle is a too large, direct impact on drilling.