How to Grind Twist Drill Bit?
The twist drill bit is a kind of common drilling tool for machining. Although it has a simple structure, it is not easy to sharpen indeed. The key lies in mastering the methods and skills. Once the methods are got, the problem will be solved easily.
1. Ensure that the blade tip is opposite to the axis and both sides are symmetrically, then slowly repaired.
Grind one edge, then the other side. It must be ensured that the cutting edge is in the middle of the axis and the edges on both sides should be symmetrical. An experienced technician will see the symmetry of tip against the light and slowly grind it. The back angle of cutting edge is generally 10-14 degrees. If the angle is large, the edge will be too thin, the vibration will be severe during drilling, the orifice will be triangular or pentagonal, and the chips will be needle-shaped. If the angle is small, the axial force during drilling will be very large, causing that it is not easy to cut in, the cutting force increases, the temperature rises greatly then the drill bit heats up seriously, and even it cannot be drilled. If the back angle is ground suitably, the front tip is centered, and the two edges are symmetrical when drilling, chip removal is brisk, the drill bit has no vibration, and the hole diameter will not be enlarged.
2. The axis of the drill bit should be inclined at an angle of 60 degrees to the grinding wheel surface.
This angle( 60 degrees ) is the point angle of the drill bit, which directly affects the size of the top angle, the shape of the main cutting edge and the angle of the chisel edge. This refers to the positional relationship between the axis and the surface of the grinding wheel, which can be seen accurately at 60 degrees. Attention should be paid to the relative horizontal position and angular position before sharpening. Both should be considered in an all-round way. Do not neglect to set the angle for setting the cutting edge, or neglect setting the cutting edge for the angle.
3. The cutting edge should swing up and down, and the tail of the drill bit should not be tilted.
This is a standard action for drill grinding. The main cutting edge should swing up and down on the grinding wheel, that is, the hand holding the front of the drill should make the drill bit swing up and down on the grinding wheel surface evenly. However, the hand holding the handle cannot swing, and the rear handle must be prevented from tilting upward, i.e. the tail of drill bit must not be tilted above the horizontal centerline of the grinding wheel, otherwise, the cutting edge will be blunt and unable to cut. This is the most key step. Whether the drill bit is worn well or not, it has a lot to do with this step. When the grinding is about to end, you should start from the cutting edge and gently rub the back corner to make the back blade smoother.
4. After sharpening the two edges, attention should also be paid to sharpening the tip for large diameter drill bits.
After the two edges are sharpened, there will be a plane at the tip of edges, which will affect the center positioning of the drill bit. So it is necessary to chamfer the angle behind the edge to minimize the plane. The method is to stick up the drill bit, align it with the angle of the grinding wheel, and pour a small groove against the blade tip at the root behind the blade. This is also an important point for centering and cutting lightly. Attention should be paid to the fact that the main cutting edge must not be worn when trimming the chamfer of the edge tip, thus it will make the front angle larger and directly affect the drilling.
5. The cutting edge should be leveled with the grinding wheel surface
Before grinding, the main cutting edge and the grinding wheel surface must be placed on a horizontal plane, that is to say, when the cutting edge contacts the grinding wheel surface, the whole edge must be ground. This is the first step of the relative position between the drill bit and the grinding wheel. After the position is set, slowly lean against the grinding wheel surface.
6. Grind back from the cutting edge.
After the cutting edge contacts the grinding wheel, it is necessary to grind from the main cutting edge to the back, that is, the cutting edge first contacts the grinding wheel, and then slowly grinds down along the entire flank. When the drill bit cuts in, it can gently contact the grinding wheel, first sharpen with a small amount, observe the uniformity of sparks, adjust the pressure on the hand in time, and also pay attention to the cooling of drill bit, so that it cannot be worn too far, causing discoloration of the cutting edge and annealing at the cutting edge. When it is found that the temperature of the blade is high, the drill bit shall be cooled in time.
So can you learn something from this article? Hope it is helpful for you.