COUNTERBORING
Counter boring:
Counter boring is an operation of enlarging a hole to a given depth, to house heads of socket heads or cap screws with the help of a counter bore tool.
Counter boring is an operation of enlarging a hole to a given depth, to house heads of socket heads or cap screws with the help of a counter bore tool.
Counterbore (Tool)
The tool used for counterboring is called a counterbore.
Counterbores will have two or more cutting edges.
At the cutting end, a pilot is provided to guide the tool concentric to the previously drilled hole. The pilot also helps to, avoid chattering while counterboring.
Counterbores are available with solid pilots or with interchangeable pilots. The interchangeable pilot provides flexibility of counterboring on different diameters of holes.
Counterbore sizes and specification:
Counterbore sizes are standardised for each diameter of screws as per BIS.
There are two main types of counterbores. Type H and Type K.
The type H counterbores are used for assemblies with slotted cheese head, slotted pan head and cross recessed pan head screws. The type K counterbores are used in assemblies with hexagonal socket head cap screws.
For fitting different types of washers the counterbore standards are different in Type-H and Type K.
The clearance hole d1 are of two different grades i.e. medium (m) and fine (f) and are finished to H13 and H12 dimensions.
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