The vertex angle of the twist drill is generally 118°, but it can also be regarded as 120°. There is generally no problem if you can master the following 6 skills for sharpening drills.
1.Before grinding the drill bit, the main cutting edge of the drill bit and the grinding wheel surface should be placed on a horizontal plane, that is to say, when the cutting edge touches 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. After the position is set, it will slowly lean towards the grinding wheel surface.
2.This angle is the front angle of the drill bit. If the angle is wrong at this time, it 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, which is 60°, which is generally more accurate. Here, attention should be paid to the relative horizontal position and angular position before the drill is sharpened. The two should be considered as a whole. Don’t ignore the angle of setting for the sake of leveling the cutting edge, or ignore the leveling of the cutting edge for the purpose of setting the angle.
3.After the cutting edge touches the grinding wheel, it should be ground from the main cutting edge to the back, that is, the cutting edge of the drill bit first contacts the grinding wheel, and then slowly grinds down along the entire flank. When the drill bit cuts in, touch the grinding wheel lightly, do a small amount of sharpening first, and pay attention to observe the uniformity of the sparks, adjust the pressure on the hand in time, and pay attention to the cooling of the drill bit, so as not to let it be ground too much, causing the edge to change color , and annealed to the edge. When the cutting edge temperature is found to be high, the drill bit should be cooled in time.
4.This is a standard drill grinding action. The main cutting edge should swing up and down on the grinding wheel, that is, the hand holding the front of the drill should evenly swing the drill up and down on the grinding wheel surface. However, the hand holding the handle must not swing, and the rear handle must not be turned up, that is, the tail of the drill bit cannot be raised above the horizontal centerline of the grinding wheel, otherwise the cutting edge will be blunted and unable to cut. This is the most critical step. Whether the drill bit is worn well or not has a lot to do with it. When the grinding is almost done, start from the edge of the blade and rub it lightly towards the back corner to make the back of the blade smoother.
1.After grinding one cutting edge, grind the other cutting edge. It must be ensured that the cutting edge is in the middle of the axis of the drill bit, and the cutting edges on both sides should be symmetrical. Experienced masters will observe the symmetry of the drill tip under bright light, and slowly sharpen it. The relief angle of the cutting edge of the drill is generally 10°-14°. If the relief angle is large, the cutting edge is too thin, and the vibration is severe during drilling. The hole is triangular or pentagonal, and the chip is needle-shaped; the relief angle is small, When drilling, the axial force is very large, it is not easy to cut in, the cutting force increases, the temperature rise is large, the drill head heats up seriously, and it is even impossible to drill. The back angle is suitable for grinding, the front point is centered, and the two edges are symmetrical. When drilling, the drill bit can remove chips lightly, without vibration, and the hole diameter will not expand.
2.After grinding the two edges, pay attention to sharpening the tip of the drill bit with a larger diameter. After the two edges of the drill bit are sharpened, there will be a flat surface at the tip of the two edges, which will affect the center positioning of the drill bit. It is necessary to chamfer the corner behind the edge to make the flat surface of the edge tip as small as possible. The method is to put the drill bit upright, 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 light cutting. Note that when grinding the chamfer of the edge tip, it must not be ground on the main cutting edge. This will make the rake angle of the main cutting edge too large, which will directly affect the drilling.
Post time: Aug-09-2023