Technical Specifications

TWIST DRILLS

TECHNICAL SUPPLY CONDITIONS OF “DAGGER DRILLS”.
1. Twist Drills are normally supplied for RH Cutting,Type ‘N’ , with a point angle ground to 118 degree and lip clearance angle minimum 8 degree.
2. Intermediate diameters , if ordered, shall be supplied with the same dimensions as of the next bigger diameter.
3. Parallel shank Drills are normally made without driving tenon.
4. Tapper Shank Drills are normally supplied with Morse taper according to IS:1715- Dimensions for self-holding tapers.
5. Non standard or special drills are manufactured against specific orders.
6. Inch Sizes drills are not recommended by Bureau of Indian Standards.
7. Other general requirements are maintained according to iso:5099 – Technical Supply conditions for twist drills.

7.1. Hardness :

Cutting Portion : 760 HV to 900 Hv.
Shank portion : 240 HV to Maximum hardness equal to cutting portion (in case of one piece construction)
Tang of Morse Taper :Sizes below 10 mm 185 Hv minimum and for sizes 10mm and above 300 Hv to 450 Hv
Driving tenon : 240 Hv to maximum hardness equal to cutting portion.

7.2. Drills are provided with a back taper of 0.02 to 0.8 mm per 100 mm flute length.
7.3. Drills are maintained with radial run out (Tr) which is calculated by equation Tr= 0.03 + 0.01 L/d (where L = Total Length & d = Drill diameter).
7.4. Twist drills are marked where diameter is 3mm and above – Drill diameter, Material (HSS) and Trademark of Indian Tool Manufacturers.
7.5. In case of twist drills below 3mm diameter the making shall be on the packing box only.

8. Twist drills acoording to Din, B.S. and ANSI are also manufactured against specific requirement.

Helix Angle For Twist Drills

Diameter Helix Angles
Over Up to and incl. Type-N (in degrees) Type-H (in degrees) Type-S (in degrees)
1.0 3.2 22-28 11-15 31-36
3.20 5.0 24-30 11-15 33-38
5.0 10.0 25-31 12-17 34-40
10.0 40.0 27-34 13-17 37-42
40.0 50.0 29-38 14-19 39-46

The Drills are made in three types for Normal(N), Hard (H) and Soft (S) work Piece materials. These type designations are based on the material to be cut and design requirements of drills.

Types of Drill Points

For Varoius Applications:
118degree point : Geneeral purpose point for most materials where work hardening or chip fromation doesnot present a problem.
135 degree : a greater point angle is used for tough or hard materials such as highly alloyed steels.
90 degree Point: a smaller point angle is used for soft and highly ductile materials such as plastics and non- ferrous matals.
Standard point with 45 degree Chamfer: a corner chamfer is used to reduce burr inb soft materials or reduce breakdown in abrasive materials.
Split or crankshaft point this type is used to reduce thrust when hand drilling tough materials or to make self-centering for NC equipment.

Cutting Fluids
Hard Tool and Alloy Steel Soluble oil compound or neat cutting oil
Low Carbon Steel Soluble oil
Copper brass or bronze Soluble oil or dry
Aluminium and magnesium alloys Soluble oil or neat cutting oil specially produced for light alloys.
Cast iron  
Stainless Steel
Nimonic alloys
Monel metals
Soluble oil can be used but Sulphurised or Chlorinated mineral or fatty oils are most suitable.
Zinc base alloys
Mazak
Soluble oil

HIGH SPEED STEELS USED FOR CUTTING TOOLS

Depending on the application, cutting tools are manufactured using different grades of HSS.The work material, its hardness, the machine tool used, part configuration,finish required on the components and volume of components to be produced are the few requirements that influence selection of different grades of HSS for manufacture of cutting tools.

Chemical Composition of some grades of High Speed Steels normally used is given below:

HSS GRADES Chemical Composition
Carbon Chronium Molybdenum Tungsten Vanadium Cobalt
M2 0.86/0.96 3.8/4.5 4.9/5.5 6.0/6.75 1.7/2.2 Nil
M35 0.88/0.96 3.8/4.5 4.9/5.5 6.0/6.75 1.7/2.2 4.5/5.2
M42 1.05/1.5 3.5/4.5 9.0/10.0 1.3/2.0 1.0/1.3 7.75/8.2
T42 1.25/1.35 3.5/4.5 3.2.4.0 9.5/10.7 2.8/3.5 9.7/10.2

TECHNICAL CALCULATIONS-DRILLING

Cutting Speed v =TT D/ 1000
D = Drill Diameter
N = Spendle speed in R.P.M.