What is countersinking?

What is countersinking?

Countersinking is an operation of beveling the end of a drill hole. The tool is called countersink.

Countersinks have edges on a conical surface.

Purpose of countersinking?

• to provide a recess for the head of countersinking screw.

• to  deburr a hole after drilling.

• for accommodating countersink rivet heads.

• to chamfer the ends of hole after thread cutting.

Angle of countersinking

            750 -  countersink riveting

            80 0 - countersink self tapping screws

            90 0 - countersink head screws and deburring.

            1200 - chamfering ends of holes to be threaded and other machining process.

Type of countersink:

Different types of countersinks are available

1. Taper shank and straight shank countersink are commonly used and they have multiple cutting edges.

2. For small diameter holes special countersinks are available. This special countersinks have two or one flute. This will reduce the vibrations while cutting.

Countersink with Pilot :

For precision countersinking after machining process these type of countersinks are used.

·         Particularly for heavy duty work it is used.

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

Countersink hole size :

According to Indian Standard the hole sizes of countersink are four types-

i) Type A, ii) Type B, iii) Type C and iv) Type E

Type A : Type A is suitable for slotted countersink head screws.

Medium and Fine grades screws are available for Type A countersink.

Type B:  Type B countersink holes are suitable for countersink head screw with hexagonal socket.

Type C : Type C countersink holes are suitable for slotted raised countersink (oval) head tapping screw and for slotted countersink bolts.

It is mainly used for steel structures. 

Some important Questions about    Countersinking:

1. The process of beveling the end of existing hole is called ?

Ans: Countersinking

2. For heavy duty work which type of countersinks are used ?

Ans : countersink with pilot

3. In a countersink why the pilot is provided ?

Ans : For guiding the countersink concentric to the hole.

4. The operation of making a cone shaped enlargement of the end of a hole is known as ?

Ans : countersink

5. For riveting purpose the angle of countersink will be ?

Ans : 750

6. The angle of countersink head screw and deburring ?

Ans : 900

7. The angle of countersink self tapping screw ?

Ans : 800

8. For chamfering ends of holes to be thread or other machining process the angle of countersink is used?

Ans : 1200

9. countersink is used for_

• Deburring a hole after drilling

• For accommodating countersink rivet heads

• Chamfer the ends of holes foe thread cutting and other machining process

10. The type of countersink are used for slotted countersink bolts those are used for steel structures ?

Ans: Type E countersink

11. Which type of countersink holes are suitable for countersink head screw with hexagonal socket?

Ans : Type B countersink

12. For slotted countersink head tapping screw (oval, head) the type of countersink

 holes are used ?

Ans : Type C countersink

13. Which type of countersink is suitable for cross recessed and slotted raised countersink head screw ?

Ans : Type A countersink