Drill bits are used to bore holes in the materials normally for fastening applications. They are made from selected high grade steels which are carefully selected for every special application.
1.General purpose drill bits. The flute geometry usually in standard helix, right hand, spiral form. The points angle is at 118° and is usually surface heat treated blue, soft shank. It is available in metric and Inch 1/16 – 1 in and its length ranges from standard to extra length.
2. Austenitic SUS drill bits. Flute geometry usually in quick helix, right hand, and spiral form. The point angle is at 118° up to 1.5mm, 135° split point 1.6mm and above. It is surface heat treated, blue, soft shank, and bronze treated for HT steel. It is available in metric and Inch 1/16 – 1 in and its length ranges from Standard length to extra length.
3.Turret, machining drill bits. The flute geometry is usually standard helix, right hand, spiral form. The point angle is at 118° to 135° split flute. It is surface heat treated, blue, and soft shank and is available in metric and Inch 1/16 – 1 in. It has a short sturdy length and Morse taper mount for arbor application. Centering drill bit are used to pilot drill on machining centers. It has a short, sturdy design, and is straight flute.
4.Straight head, chisel tip, carbide insert drill bits. Its flute geometry are straight + std helix, right hand, and spiral. It also has a straight head, carbide inset tips are used to drill hard. Treated materials with small chips and continuous penetration even hot. Its point angle is usually at 135° double point.
6.Carbide insert drill bit (for Masonry). The flute geometry is Standard helix, right hand, and spiral. It has a brazed carbide inset tips are used to drill on concrete. Flute is HSS Treated impact steel materials where concrete drilling requires hammer action. The point angle is at 135°.
7.Wood and thin metal sheet drill. Comes in straight flute geometry and has a piloted tip and wings used for sharp cutting lips.
8.An auger bits are used for wood application and has a broad auger flute for fast chip removal.
Now that we know the different types of drill bits, it is also important to know some tips while using the drill bits:
1.Primary concern in drilling are the; size of the drill hole and depth, location accuracy and axis geometry, Material to be drilled (properties), drill speed and feed rate and the drilling tool to be used.
2.Drill bits being a centrifugal cutting tool, normally cuts the whole diameter slightly bigger than the drill bit major diameter. This has to be carefully considered for precision drill holes, that reamer or other applicable machining finish will make the final cut.
3.End point of a drill bit is a horizontal lip and not a point dot where it can precisely start at hole at that specific spot. A pre-punched hole or center drilled hole has to be made prior to drilling process. Perpendicularity must be carefully observed.
4.Consideration of material and bit is also a concern in drilling. Cast iron, brass can be drilled with loose tiny chips, while SUS is drilled with spiral continuous chip. The chip removal is a concern with regards to flute and helix design. If chips are not properly taken out of the hole, this will seize and break the drill bit, or destroy the hole.
5.Drill bit rpm plays critical role in drilling with consideration to rate of cut (mm/min) versus drill diameter and number of flute. To determine the correct drilling rpm, use the following formula :
[(fr mm/min) x (fl # flute) / tool bit diameter ]x 700 = RPM
Where; (700 constant is derived from average machinability of most of the iron materials)
Example 1.
fr = 1mm/min 1 x 2
fl = 2 = -------- x 700 = 280 rpm
Tb = 5mm 5mm
RPM = [1x2 / 5mm] x 700
= 280 rpm
This calculation of rpm however is generic for general purpose drilling. The Tool maker has the option to determine the appropriate rpm for different materials being drilled. Example is the color of chips and temperature. Material being drilled and finish needed
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