Four tips for sharpening twist drills
“Small grinding” is first of all “no grinding”. When you get the drill bit, you can grind it in a hurry. It must be blind grinding. Only by placing a good position before sharpening can we lay a solid foundation for the next step of “sharpening”. This step is very important.
Here are four sentences to guide the sharpening process, the effect is better.
Formula 1: “The blade is flat against the surface of the wheel.”
This is the first step in the relative position of the drill bit and the grinding wheel. Often students start sharpening by leaning on the grinding wheel before the cutting edge is leveled. This is definitely not good. Here, the “cutting edge” is the main cutting edge, and “swing flat” means that the main cutting edge of the sharpened part is in a horizontal position. “Wheel surface” refers to the surface of the grinding wheel. “Kai” means to move closer slowly. At this time, the drill bit cannot touch the grinding wheel.
Mantra 2: “The drill shaft releases the front angle obliquely.”
here refers to the positional relationship between the axis of the drill bit and the surface of the grinding wheel. The “front angle” is half of the apex angle of 118°±2o, which is about 60°. This position is very important, and it directly affects the size of the apex angle of the drill bit, the shape of the main cutting edge and the bevel angle of the chisel edge. It is necessary to remind students to memorize the angles of 60° in a 30°, 60°, and 90° triangle plate, which is easy for students to master. Formula 1 and Formula 2 both refer to the relative position of the drill bit before sharpening. Both should be considered. Do not neglect the bevel angle for the purpose of leveling the cutting edge, or neglect the leveling of the cutting edge for the purpose of setting the inclined axis. These errors often occur in actual use. At this time, the drill bit is ready to contact the grinding wheel when it is in the correct position.
Mantra 3: “Wear the back from the blade to the back.”
here means to sharpen slowly along the entire back from the cutting edge of the drill. This facilitates heat dissipation and sharpening. On the basis of stabilizing and consolidating formulas one and two, the drill can lightly touch the grinding wheel to perform a smaller amount of sharpening. When sharpening, observe the uniformity of sparks, adjust the pressure in time, and pay attention to the cooling of the drill. When the sharpening is restarted after cooling down, the positions of formula one and two should be continued. This is often not easy to grasp when beginners, and often involuntarily change the correctness of its position.
Phrase 4: “Do not swing the tail up and down.”
This action is also very important in the process of sharpening the drill. Often students change the “swing up and down” to “turn up and down” during sharpening, causing the other main edge of the drill to be destroyed. At the same time, the tail of the drill bit cannot be raised above the horizontal centerline of the grinding wheel, otherwise the cutting edge will be blunt and cannot be cut.