When sharpening drill bits, special attention should be paid to the angle at the vertex, axis rear angle, length of the transverse cutting edge back taper and the front corner of Potocki transverse cutting edge.
Liane of the apex angle 2φ of the drill when grinding is caused by the change of thickness a and width b of the cut when drilling with increasing angle 2φ, increased thickness and reduced width of cut.
the Back angle α is an important design element of the drill to which you should pay attention when sharpening drill bits. Its magnitude has a significant impact on the work of the friction forces and, consequently, the temperature in the cutting zone. When the temperature in the cutting zone of the processed material begins to actively absorb atmospheric gases, resulting in higher strength and lower ductility by altering the cutting process and the resulting inhomogeneity of the surface quality. The increase in the angle α when sharpening drill bits reduces friction, but reduces the rigidity, which leads to vibration of the drill and reduce the accuracy of the drilling.
clearance angle
Rear angle on top of drill bits for metal forming on the machine for sharpening of drills conical or plane sharpening. Stocktake when the conical surface is a smooth decrease in the rear corner. With a dual plane sharpening of the drill point are ground to a straight plane, to reduce the friction of the rear surface when drilling on the surface additionally remove a layer of material at an angle of 20-25°.
Transverse cutting edge
Transverse cutting edge worsens the process of penetration of the drill into the detail so its length reduces with the help of Potocki on the machine when sharpening drill bits. Reduce the length of the transverse cutting edge reduces the axial component of force by 25% compared to a drill without Potocki. Excessive decrease in the length of the transverse cutting edge leads to an increase in vibrations of the drill during cutting. The gun nose of the transverse cutting edges of drills can be of four types.
Form of Potocki
When you gun nose form A transverse cutting edge is undermined when sharpening drill circle with the formation of the concave curved surface. The gun nose shape In allows to undermine a transverse cutting edge with the grinding of the front surface along the straight path, aligning a cutting edge of the drill. The gun nose shape With saps transverse cutting edge with the outlet at an angle to the front surface of the tool. Circular gun nose undermines the transverse cutting edge with the formation of a convex curved surface.
angle
twist drill bit has a small amount of the front angle γ in points at the transverse cutting edge, which impairs the cutting process, the Central part of the drill. Allows the gun nose to the front corner of the transverse cutting edge. Excessive increase in the angle γ larger than the angle of inclination of the helical grooves, increases narezanie surface Potocki the front surface of the drill forming a hole with radius R. The hole prevents a descent chip and contributes to its sticking to the surface of Potocki that leads to a reduction in processing accuracy when cutting.
