How to grind a good Rock Button Bits:
Good Rock Button Bits must meet the following characteristics:
①The top angle 2 is 118°±2o
②The clearance angle α0 at the hole edge is 10°-14°
③Chisel edge bevel angle is 50°-55°
④The length of the two main cutting edges and the two angles formed by the axis of the Rock Button Bits must be equal
⑤The two main flank surfaces should be sharpened smoothly.
But theory alone is not enough. Students should stand in front of the grinder and do it by themselves, instead of blindly sharpening them. If you are not instructing students on the methods and skills of sharpening hand-in-hand, then a student with good theoretical knowledge, if you ask him to sharpen a standard twist drill at a time, it is impossible to drill. why? Theory has not yet guided practice. Students have not mastered the skills and techniques of sharpening. Although the commonly used standard twist drills only sharpen the two main flank faces and sharpen the chisel edge, after sharpening, ensure that the top angle, the chisel edge bevel angle and the length of the two main cutting are equal, and the left and right sides are equal in height. Moreover, after grinding the chisel edge, it is indeed difficult to make Rock Button Bits cut briskly during the drilling process, and chip removal is normal. We must first help students build confidence, which determines motivation. After mastering the methods and skills, it is not difficult to sharpen a qualified standard twist drill. Secondly, we must clearly tell them to watch less and sharpen them blindly. The more they sharpen, the more blindly they are. They have finished grinding a long Rock Button Bits, and they don't know why. Only by studying less, analyzing more and understanding more can theory slowly guide practice. To grind less means to grind less, or even not, when you can't do it. This can save the waste caused by blind sharpening, and you can also study how to sharpen with great concentration. To read more is to read the knowledge and illustrations in the books, the sharpening actions of the teacher, the qualified standard twist drills that have been sharpened, and all kinds of twist drills with sharpening defects. It is very important to look at it quietly and look at it carefully. So that they have a basic understanding of the "good" and "bad" of twist drills.
"Small grinding" First "not grinding", get Rock Button Bits to grind quickly, 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. In the process of demonstration, teachers can explain and demonstrate in the form of easy-to-understand formulas based on the methods and techniques summarized in practice. Students often understand and understand. Do a good job in the demonstration of normal movements, step-by-step movements, and slow-motion demonstrations so that students can easily accept them. Here are four phrases to guide the sharpening process. The effect is better.
Mouth 1: "The edge of the blade is flat against the wheel surface." This is the step of the Rock Button Bits relative to the grinding wheel. Often students start sharpening by leaning on the wheel before the edge is leveled. This is definitely not good. The "cutting edge" here 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. At this time, Rock Button Bits cannot touch the grinding wheel.
Formula 2: "The drill shaft releases the front angle obliquely." This refers to the positional relationship between the axis of the Rock Button Bits 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 directly affects the size of the apex angle of Rock Button Bits, 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 Rock Button Bits before sharpening. The two should be taken into account. Don't neglect the bevel angle for the purpose of leveling the edge, or neglect the leveling of the edge for the purpose of arranging the inclined axis. These errors often occur in actual operation.
Let’s say that twist drill is a professional drilling tool, so its application is also specific, and it has fulfilled an irreplaceable role in a lot of ways. However, it also has some defects of its own:
It is understood that the twist drill is mainly composed of the shank, the neck and the working part. Although the geometric shape of the twist drill is more reasonable than that of the flat drill, it still has the following shortcomings:
1. Compared with other types of cutting tools, the main cutting edge of standard twist drills is very long, which is not conducive to chip separation and chip breaking.
2. The chisel edge is too long, and the rake angle of the chisel edge is very negative, reaching -54°～-60°, which will generate a large axial force.
3. The secondary clearance angle of the secondary cutting edge at the edge of the twist drill is zero, which causes the friction between the secondary flank face and the hole wall to increase, and the cutting temperature rises. The outer corners of the Rock Button Bits are worn out and have been machined. The surface roughness deteriorates.
4. The rake angle value at each point on the main cutting edge of a standard twist drill is too different from inside and outside. The rake angle of the main cutting edge at the outer edge of Water Well Drilling Tools is about +30°; and the rake angle is about -30° near the drill center. The rake angle near the drill center is too small, resulting in large chip deformation and high cutting resistance; and The rake angle near the outer edge is too large, and the cutting edge strength is often insufficient when machining hard materials.