Main Technical Conditions Of Twist Drill
Dimensions
Drill diameter
The values indicated in the relevant dimensional standards apply in respect of the diameter od Twist Drills
Test point:On the lands at the corners,(see Fig.1)
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 0.08 mm over a length of 100mm.
Test point:At the outside diameter and indicating measuring instruments

Parallel shank
Tolerance for shank diameter f11, Tolerance for roundness and parallelism 0.02mm for the shank length

Concentricity tolorance(tr.)
The concentricity tolerance(tr.) of the Twost Drill is calculated from the equation.
Tr=0.03+0.01*1/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°σ=135°
Test point:At the cutting edges(See Fig.2)
Testing equipment:Universal bevel protractor indicating measuring instruments

Materials and hardness
Materials
M2;M35;M42;F4341;9341or4341;
Hardness
HSS HRC63-66
HSSCO HRC64-68
Test point:On outside diameter on the land or adjacent relieved land
Test equipment:Hardness Tester

Marking
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