►Twist drill mainly include rake angle and back angle, angle of the two had a great influence on drilling, angle before the bit edge to linger-sometimes constantly decreases, and then angle from the bit edge to linger-sometimes constantly increased gradually.
(1) reference frame of the twist drill
Twist drill has more complex shape and cutting parts: for the purposes of marking its geometric parameters, it&rsquo s based on the structure characteristics of twist drill and movement characteristics of the work, in addition to the base level cutting plane, orthogonal plane also used the end plane, column section and section which are defined as follows.
Flat end: twist drill axis perpendicular to the plane. This plane is also from any point on the cutting edge of the back plane, and vertical and base level of the store.
Column section: the main cutting edge in office a bit column section by that point, and at that point the radius of gyration radius and twist drill axis as the axis of cylinder. It works with that point of tangent plane and reference plane vertical at the store.
In profile: through the axis of the twist drill, and with two main cutting edge parallel to the axial section.
(2) the angle of twist drill geometry
1) the apex angle 2 &Phi
It is two main cutting edges within the section in the projection angle. Apex angle is smaller, the longer the main cutting edge, the unit on the cutting edge load, axial force decreases, and the axial stability of drilling. And external circular knife angle increases is good for heat dissipation and improve the tool life. But the apex angle can make drill point intensity abate, the increase of chip deformation can increase torque. Standard twist drill point angle is about 118 ° . HSS HSS drill: apex angle is 118 ° , sometimes more than 130 ° , HM carbide drill: apex angle is 140 ° commonly Straight flute drill often is 130 ° , three blade drill is 150 °

1) the main angle and the end face of blade angle

Twist drill master choose designated the main cutting edge angle is on the base point at where the main cutting edge projection and drilling the angle between the direction of feed. Because of twist drill, the base is different at various points on the main cutting edge of the angle change. After vertex angle 2 &Phi twist drill grinding, the main angle of each point is determined the relationship between them.
Tan = tan &Phi cosine type (2 – (2))
the end face of blade angle of the selected point, it is the primary cutting edge projection and in the end point of the angle between the reference plane.
Because of each point on the cutting edge blade dips from outer guide linger-sometimes constantly grow bigger, so that each point on the cutting edge is the main angle of outer edge is big, small linger-sometimes constantly.

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