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How to grind a twist drill?
2021-06-09

Twist drills are the most commonly used cutting tools. To sharpen twist drills, you must pay attention to some points:

Twist drill is a commonly used drilling tool for mechanical processing. Although the structure is simple, it is not easy to sharpen it. The key lies in mastering the methods and skills of sharpening. If the methods are mastered, the problem will be solved. Here I will introduce the manual sharpening techniques for twist drills.

The vertex angle of twist drill is generally 118°, but it can also be regarded as 120°. Sharpening drills mainly master several skills:

1. The cutting edge should be level with the surface of the grinding wheel.

Before grinding the drill bit, the main cutting edge of the drill bit and the grinding wheel surface should be placed on a horizontal surface, that is to say, when the cutting edge contacts the grinding wheel surface, the entire edge must be ground. This is the first step in the relative position of the drill bit and the grinding wheel. Set the position and then slowly lean on the surface of the grinding wheel.

2. The axis of the drill bit should be inclined at an angle of 60° with the surface of the grinding wheel.

This angle is the front angle of the drill bit. The angle at this time is incorrect, which 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 takes 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 consideration. Don't neglect the angle to flatten the edge, or neglect to flatten the edge for the angle.

3. Grind the back from the cutting edge.

After the cutting edge touches the grinding wheel, it should be ground from the main cutting edge back, that is, the cutting edge of the drill starts to touch the grinding wheel, and then slowly grinds down the entire flank surface. When the drill bit is cut in, you can lightly touch the grinding wheel, first perform a smaller amount of sharpening, and pay attention to the uniformity of the sparks, adjust the pressure on the hand in time, and pay attention to the cooling of the drill bit. , And to the edge annealing. When the cutting edge temperature is found to be high, the drill bit should be cooled in time.

4. The cutting edge of the drill bit should swing up and down, and the tail of the drill bit cannot be lifted.

This is a standard drill grinding action. The main cutting edge must swing up and down on the grinding wheel, that is, the hand holding the front of the drill must evenly swing the drill up and down on the grinding wheel. However, the hand holding the handle cannot swing, and the rear handle must not be tilted upwards, that is, the tail of the drill bit cannot be tilted higher than the horizontal center line of the grinding wheel, otherwise the cutting edge will be blunt and unable to cut. This is the most critical step. The quality of the drill bit has a lot to do with it. When the grinding is almost the same, start from the edge of the blade and rub it slightly toward the back corner to make the back of the blade smoother.

5. Make sure that the tip of the blade is aligned with the axis, and both sides are symmetrical.

After the edge of one side of the drill is sharpened, sharpen the edge of the other side. Make sure that the edge of the drill is in the middle of the axis of the drill, and the edges of both sides should be symmetrical. An experienced master will observe the symmetry of the drill tip with bright light and slowly sharpen it. The relief angle of the cutting edge of the drill bit is generally 10°-14°. The relief angle is large, the cutting edge is too thin, the vibration is severe during drilling, the hole is triangular or pentagonal, and the chips are needle-shaped; the relief angle is small, When drilling, the axial force is very large, it is not easy to cut, the cutting force increases, the temperature rise is large, the drilling hair is hot, and it is even impossible to drill. The rear angle is suitable for angle grinding, the front tip is centered, and the two edges are symmetrical. When drilling, the drill bit chip evacuation is brisk, without vibration, and the hole diameter will not be enlarged.

6. After the two blades are sharpened, pay attention to sharpening the tip of the drill bit with a larger diameter.

After the two blades of the drill are sharpened, there will be a flat surface at the tip of the two blades, which affects the center positioning of the drill. It is necessary to chamfer the angle behind the blade to make the flat surface of the blade tip as small as possible. The method is to erect the drill bit, align it with 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 for drill centering and cutting briskly. Note that when grinding the chamfer of the cutting edge, do not grind it to the main cutting edge, as this will make the rake angle of the main cutting edge too large and directly affect the drilling.

Of course, there is no fixed formula for grinding drills. It is necessary to accumulate experience in actual operation. Through comparison, observation, and trial and error, the drill will be grind better.


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