Main Technical Conditions Of Twist Drill (2)

1). Dimensions Drill diameter The values indicated in the relevant dimensional standards apply in respect of the diameter of Twist Drills.
Test point: On the lands at the corners,(see Fig.l)

 Testing equipment: micrometer
Tapering of diameter: The diameter of twist drills usually reduces from the drill tip towards the shank in the area of the flutes.
Test values: The taper on diameter amounts to 0.02 to 0.08mm over a length of 100mm.
Test point: At the outside diameter on the land.
Testing equipment: micrometer and indicating measuring instruments.
Parallel shank :Tolerance for shank diameter f11,Tolerance for roundness and parallelism 0.02mm for the shank length.
Concentricity tolerance(Tr.) The concentricity tolerance(Tr.) of the Twist Drill is calculated from the equation.
Tr=O.03+O.O1¹/_d
In which I is the total length and d the diameter of the drill (all dimensions in mm)
Length: The tolerance of length for the total length corresponds for the degree of accuracy very coarse according to DIN 7168 part 1.The flute lengths given in the relevant dimensional stands are minimum dimensions.
Point angle: Test value:σ=118°;σ135°
Test point: At the cutting edges(See Fig.2)
Testing equipment: Universal bevel protractor indicating measuring instruments.

2). Materials and hardness Materials: M2; M35i M42; F4341; 93410r4341;
Hardness: HSS HRC63-66
HSSCO HRC64-68
Test point: On outside diameter on the land or adjacent relieved land.
Test equipment: Hardness Tester.
3). Making: Twist drills with diameter 3mm and upwards shall be marked with:
Diameter
Material:(HSS;HSSCO;)
Name or mark of manufacturer.
Additional and/or differing marking by agreement.

4). Twist Drill with parallel shank

5). Twist Drill with taper shank

6). General dimensions of morse taper shanks

7). 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.

8). 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 angleγ are measured in the tool orthogonal plane. For details, see DIN 6581, definitions of metal-cutting technology; geometry at the tool edge.
9). 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.

10). Margin width bα 

Test values: The land width as in Fig.3 shall lie within the limiting values indicated in Fig.4 

Test point: 5mm behind the corner
Testing equipment: Slide gauge 

11). 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 width bα
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 execution 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
12). Re-sharpening Twist drills 

(1) Drills are worn off irregularly. It should be sharpened prior to developing into excessive wear.(2) Re-sharpening
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)
13). Web Thinning 

(1) Without thinning
Suitable for drill of general purpose. Thanks to thin web thickness, web thinning is not need.
This without web thinning type is applied to design of drills for mild steel, alloy steels, cast iron, stainless steel, titanium, inconel, etc. and conventional cutting conditions.

(2) Type C thinning (DIN 1412 FORM C,SPLIT POINT)
Because Split point enables good centering
when drilling and breaks the chips, chip removals is easy.
Suitable for drill design in high hardened tough materials ,i.e, heat treated steel, titanium alloy, stainless steel, incoroy inconel, nimonic, etc.

(3) Type R thinning (HEI.ICAL THINNING)
Helical thinning ensure to frequent chip breaking and removal. The different direction force of cutting edges and helical thinning parts enables that chips curl, break and remove through the flutes. In addition helical thinning makes the chip room up to center, remove the chisel and enables good centering.(4)Type A thinning (DIN1412 FORM A)
A type thinning makes thin chisel, good chip removal and favorable centering.
This type is the easiest type to grind the thinning. In narrow web and wide fluted drills, keeping of the rigidity and smooth chip removal are possible.(5) Type B thinning (DIN1412 FORM B)
In case of work materials with low cutting resistance and good chip removal,ie,cast iron, aluminium, plastic etc, B type thinning is suitable.
Especially when drills for high hardened steels are designed, this type is applied to decrease rake angle and avoid chipping of cutting lips.