1. Grinding bits generally use grinding wheels with a particle size of 46-80 mesh, and aluminum oxide grinding wheels with medium to soft hardness are preferred. It is required that the grinding wheel runs smoothly, and grinding wheels with large runout must be trimmed. In order to smoothly grind the transverse edge of the drill bit, the outer corner of the grinding wheel must be trimmed to a smaller radius. If the radius of the fillet is too large, it will damage the main cutting edge when grinding the transverse edge.
2. When the drill bit is cooled, the pressure applied by the drill bit during grinding should not be too large. Generally, air cooling is used, and if necessary, water should be dipped for cooling to prevent overheating and annealing from reducing the hardness of the cutting part of the drill bit.
3. The standard Fried Dough Twists drill has a long horizontal edge, which is generally 0.18D (D refers to the diameter of the drill bit), and the front angle at the horizontal edge has a large negative value. Therefore, the cutting at the horizontal edge is in an extrusion state when drilling, and the axial resistance is large. At the same time, the length of the horizontal edge causes poor centering effect and cutting stability. Therefore, the drill bit with a diameter of more than 5mm must have a short horizontal edge, and the front angle near the horizontal edge should be appropriately increased to improve the cutting performance of the drill bit.
The grinding of the transverse edge is necessary. The purpose of transverse edge grinding is to shorten the transverse edge, but it cannot be too short. A too short transverse edge cannot reduce the feed resistance. During the process of shortening the transverse edge, try to grind the negative front angle on both sides of the transverse edge as much as possible. Properly increasing the front angle at this point can reduce the cutting resistance during the cutting process, making the entire drilling process light and fast.
4. If the drill bit is manually fed. The tip angle can be appropriately reduced during the grinding process. Due to insufficient feed pressure of the electric hand drill, reducing the tip angle appropriately can increase the positive pressure of the cutting edge on the cutting surface.
If the requirements for the aperture and surface roughness of the processed hole are not very strict, the two cutting edges can also be appropriately ground into incomplete symmetry. Although the hole diameter will increase on the original basis during the drilling process, it can significantly reduce the friction between the drill bit edge and the hole wall, reducing cutting force. There is no strict formula for grinding drill bits, which requires gradually accumulating machining experience in the actual operation process, constantly repeating experiments, gradually comparing, and observing, to ensure that the drill bit edge can be ground well.
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