A countersink makes a conical hole and is normally used to seat a flathead screw.
A counterbore can refer to a cylindrical flat-bottomed hole, which enlarges another hole, or the tool used to create that feature.
- Counter-sinking is opten done to accomodate heads of flat head screws.
However as can be seen from the figure below, there is a sideways component of the thrust which could split the countersink
due to the generated hoop stresses.
Countersink examples at different angles.
To accurately drill your countersunk holes, we will need the following information.
1. Angle of the drill
2. Major Diameter (finished diameter of the hole at the surface)
3. Depth the countersink is to be drilled
4. Which side of the board is the sink on? Top or Bottom?
5. The finished diameter of the shaft of the hole
6. Is the sink and shaft to be plated or non-plated?
- Counter-boring is done to accomodate pan-head, fillister-head or round head screws or other screws with flat-bottomed undersides.
- Counter-bored screws exert only force in the axial direction, thus operate mostly under compression, with no sideward component
to the applied force vector. Such design is inherently more robust than counter-sinking.
To fabricate your counterbored holes, we would need to know the following information.
1. Major Diameter (finished diameter of the hole at the surface)
2. Depth the countersink is to be drilled
3. Which side of the board is the sink on? Top or Bottom?
4. The finished diameter of the shaft of the hole
5. Is the bore and shaft to be plated or non-plated?
Because the sides of the hole are always parallel, there is no need to specify an angle.
|Nominal||Thread.||Hex Socket Size||Body diameter and Head height||Head Dia||Soc. length|
Countersunk Screws (Flat Head Screws)
The dimensions are generally in accordance with BS EN ISO 10642:1998. This supersedes BS 4168-8.
|Nominal size||Body Dia||Thread Pitch||Hex Socket Size||Max Cone Dia||Head Dia||Head Height||Soc. length|
illustrations above is from Jim Svatos — PCB Universe, Inc.