Types of countersinking

 Countersinking

.what  is countersinking

. list the purpose of countersinking

. the angles of countersinking for the different applications

. name the different types of countersinks

What is countersinking

Countersiniking is an operation of bevelling the end of a drilled hole. The tool used is called a countersink.

Countersinking is carried out for the following purposes, to provide a recess for the head of a countersink screw, so that it is flush with the surface after fixing to deburr a hole after drilling for accommodating countersink rivet heads to chamfer the ends of holes for thread cutting and other machining processes.

Angles for countersinking

Countersinks are available in different angles for different uses.

75° countersink riveting

80° countersink self tapping scew

90° countersink head screws and deburring

120° chamfering ends of holes to be threaded or other machine processes.

Countersinks

Countersinks of different types are available

The commonly used countersinks have multiple cutting edges and are available in taper shank and straight shank.

For countersinking small diameter holes special countersinks with two or one flute are available this will reduce the vibration while cutting.

COUNTERSINKS WITH PILOT

For precision countersinking, needed for machine tool assembling and after machining process, countersinks with pilots are used.

They are particularly useful for heavy duty work.

The pilot is provided at the end for guiding the countersink concentric to the hole.

Countersinks with pilots are available with interchangeable and solid pilots.

Countersink hole sizes

The countersink holes according to Indian standard IS 3406(part 1) 1986 are of four types. Type A, type B, type C and type E.

The type A is suitable for slotted countersink head screws, cross receessed and slotted raised countersink head screw.

These screws are available in two grades i. e medium and fine.

The dimensions of various features of the type A countersink holes.

Type B countersink holes are suitable for countersink head screws with hexagon socket.

Type C countersink holes are suitable for slotted raised countersink(ovel) head tapping screws and  for slotted countersink(flat) head tapping screws

Type E countersinks are used for slotted countetsink bolts used for steel structures.