TABLE OF CONTENTS The level of importance placed on the dimensional integrity of a simple tapered or countersunk hole varies widely [1]. The reason for the taper on such a hole runs the gamut ranging from "to make the hole look nice" to "preventing catastrophic failure." It is not likely that a 60-degree countersink will make the hole look any nicer than a 100-degree countersink; but an angle a bit off here or a taper depth a bit too short there might indeed cause something to fail catastrophically, just as the lack of sealing caused a catastrophic space mission failure. The individuals making the product often do not know what the product eventually may do or how it is used. In most cases the decision of whether something has been produced right or wrong has been reduced to a straightforward matter of determining whether or not stated specifications have been met. It is the part drawing that defines what is and is not to be. Parts are measured to verify conformance.
The dimensional measurement of tapered holes presents some unique problems. An understanding of the basic geometry involved will better prepare the designer to more efficiently define needs and help the inspector to choose the proper tools and apply them successfully.
Whether we call them countersinks, chamfers, centers, or tapered holes, these features always share the three common dimensional components of any female conical form: major diameter, taper depth, and angle (Fig. 10-1).
