Cutting portion

σ= Point angle (sigma)
ψ = Chisel edge angle(psi)
*)In the context of cutting technology, land width b is the body clearance land width which is to be by b_fan see DIN 6581.

Angle at the cutting edges

The corner has been adopted as the observed edge point

α_x=Side clearance angle (alpha)
α_xe=Effective side clearance angle
β_x=Side wedge angle(beta)
γ_x=Front rake angle(gamma)
γ_xe=Working front rake angle
η=Resultant cutting speed angle(eta)

Clearance angle α,wedge angle β and rake angleγare measured in the tool orthogonal plane. For details, see DIN 6581, definitions of metal-cutting technology; geometry at the tool edge.

Web thickness K

Test values:The web thickness according to Fig.1 shall not be less than the minimum value k_min indicated in Fig.2.
Test point: At the point of the drill.
Testing equipment:Slide gauge with measuring points.

Margin width bα

Test values: The land width as in Fig.3 shall lie within the limitting values indicated in Fig.4
Test point: 5mm behind the corner
Testing equipment: Slide gauge 

Angle on twist drills

(1)Side rake angle γ_f (Helix angle)
Recommended test value: Recommended ranges depending on the tool types N,H and W according to DIN 1836 and the diameter of the drill included in Fig.5
Test point: At the corner, see Fig.6
Testing equipment: According to VDI Guideline 3331 Part1 ,Section Margin widthbα
Note:The side rake angle γ_fis measured in place of the orthonagonal rake angle γ_o found in the wedge measuring plane(see DIN 6581),as this changes along the cutting edge(becoming smaller towards the point of the drill)
　

(2) Point angle σ
test value: Usual executin for tool types N and H:σ =118°,for tool type W:σ =130°
Test point: At the cutting, see Fig.7.
Testing equipment: According to VDI Guideline 3331 Part 1, Section Margin width b_α
　

Resharpening Twist drills

(1) Drills are worn off irregularly.It should be sharpened prior to developing into excessive wear.
(2) Resharpening
①Grind the correct point angle to suit your application.(figure 8)
②Check that both cutting lips have the same angle. On a 130° point,each lip should be 65° toward the axis.The point must be on center, i.e.,the chisel edge must produce cutting lips of equal length.(figure 8)
③Grind Primary relief and Secondary clearance,(figure 9)
④Grind web thinning.(figure 10)