4.Drill cutting edge need to swing up and down, the tail can not warped.
This is a standard drill grinding operation, the main cutting edge need to swing up and down on the wheel, that is to say the front hand grip portion of the drill bit need to uniformly swing up and down on the wheel surface. The hand griping portion can not swing, but also to prevent the handle to the upturned, that is to say the end of the drill bit can’ t upturn above the center line of the wheel level, otherwise it would blunt the blade and can not cut. This is the most critical step, and this has a great relationship with whether the bit worn well or worse. When the worn almost finished, you need to rub back angle from the beginning edge then gently rub back and let some of the back edge more smooth.
5. To ensure that the cutting edge face the axis and slowly repair with bilaterally symmetrical.
After grinding the side edge, and then grinding the other side of the blade, the blade must be guaranteed in the middle of the drill, axis should be symmetrical on both sides of the blade. Experienced instructors will drill point of view against the light symmetry and grinding slowly. After the drill cutting edge angle is generally 10 ° -14 . the angle is large, so the cutting edge is too thin, powerful vibration when drilling, was triangular or pentagonal orifice, needle-like chips posterior horn small, When drilling axial force is large, easy to cut, increase cutting force, temperature large, drill severe fever, not even drilling. Clearance angle grinding fit, angle top pair, edged symmetry, while drilling, drill chip light, no vibration, the aperture can not expand.
6, When two grinding is completed, we also need to note the angle top that larger diameter drill bit grind drill .
Two drill grinding is completed, there will be a he plane at the two-edged angle top effecting the drill centering, we need to look down the back of the blade angle to grind the plane of the blade tip as small as possible. The method is to erect the drill, aligned wheel angle, the roots behind the blade, blade tip facing down a slot. It is also an important part to brisk centering and cut point. Note when grinding the blade edge chamfering, do not grind to a main cutting edge, it would make the main cutting edge of the rake angle being too large, the direct impacting drilling.
Of course, there is no certain set about grinding drill style, we need to accumulate experience in practice. We would mill drill better by comparison, observation, trial and error.

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