twist drill bits

Processing effect

(1) the diameter of twist drill is limited by the aperture, the spiral groove makes the drill core thinner, the Drill Bit stiffness is low; With only two ribbed guides, the axis of the hole is easy to skew; The horizontal edge makes centering difficult, axial resistance increases, and the bit is easy to swing. Therefore, the shape and position error of the drilled hole is large.

(2) twist drill before and after the tool surface are curved, along the main cutting edge of each point of the front Angle, the rear Angle is not the same, the front Angle of the horizontal edge of -55°. Poor cutting conditions; The distribution of cutting speed along the cutting edge is not reasonable, and the cutting speed of the tip with the lowest strength is the highest, so the wear is serious. Therefore, the hole precision of processing is low.

(3) The whole edge of the main cutting edge of the drill participates in cutting, and the cutting speed of each point on the edge is not equal, which is easy to form spiral chips and difficult to discharge chips. Therefore, the chip and the hole wall extrusion friction, often scratch the hole wall, the surface roughness after processing is very low

Operation method

"Less grinding" is the first "no grinding", get the drill in a hurry to grind, is certainly blind grinding. It is very important to position yourself well before grinding to lay a solid foundation for the next step of "good grinding".

Here with four formula to guide the grinding process, the effect is better.

Formula one: "edge to balance the wheel surface."

This is the first step of the relative position between the drill bit and the grinding wheel. Often, some students lean on the grinding wheel to start grinding before the edge is balanced. This is definitely not going to grind well. The "edge" here is the main cutting edge, and the "leveling" means that the main cutting edge of the part being ground is in a horizontal position. "Wheel surface" means the surface of the grinding wheel. "Lean" means to draw closer slowly. At this point, the drill can not contact the grinding wheel.

Formula two: "drill shaft oblique release front Angle."

Here refers to the position relationship between the bit axis line and the grinding wheel surface. "Edge Angle" is half of the tip Angle 118°± 2O, about 60° This position is very important, directly affects the size of the tip Angle and the shape of the main cutting edge and the bevel Angle of the edge.Students should be reminded of the common 30°, 60°, 90° triangle board in the 60° Angle, students easy to master. Formula 1 and formula 2 are the relative position of the drill before grinding, both should be taken into consideration, not to balance the edge and ignore the bevel Angle, or to balance the oblique axis and ignore the edge. These errors are often made in practice. At this point, the drill bit is ready to contact the grinding wheel in the correct position.

Tip 3: "from the blade to the back grinding back."

In this case, grinding is done slowly from the edge of the bit along the entire back surface. This facilitates heat dissipation and grinding. On the basis of stable consolidation of tips 1 and 2, the bit can gently contact the grinding wheel for a small amount of grinding. During grinding, the uniformity of spark should be observed, the pressure should be adjusted in time, and the bit cooling should be paid attention to. When cooling back to grinding, to continue to set the position of formula one and two, which is often not easy to master in the beginning, often can not help but change the accuracy of its position.

Formula four: "up and down swing tail do not become warped."

This action is also very important in the process of bit grinding, often students in the grinding "swing up and down" to "turn up and down", so that the other main blade of the bit was destroyed. At the same time, the tail of the drill bit should not be tilted above the horizontal center line of the grinding wheel, otherwise the edge will be blunt and unable to cut.