Section 3 Unit 6 Drilling, Threading, Tapping and Reaming

tap

An internal thread is cut in the inside diameter of a workpiece with this cutting tool

chamfer

Countersinking is also frequently performed to create a ____ at the opening of a hole to allow easier entry of pins, aid in starting taps, and for deburring

Plug chamfer

are the most general purpose of the three chamfer types and they are either used by themselves or after a taper tap when it is necessary to thread deeper

pitch diameter

diameter the imaginary diameter measured where the thickness of the thread and space within the groove are equal

nominal major diameter

for inch series threads, the first number shown

twist drill

general-purpose hand drilling is usually done with this bit.

Unified Thread Standard

has established dimensional standards for the consistent interchange of threaded parts for inch series threads

gun taps

have straight flutes with a special angle ground on their ends

counterboring

increases the diameter of a hole to a certain depth in order to allow a screw head or nut to be positioned flush with or below the workpiece surface

thread

is a spiral groove made on a round external or internal diameter

pitch

is the distance from a point on one thread to the same point on the adjacent thread

major diameter

is the largest diameter of a thread

crest

is the peak of one thread and creates the points from which the major diameter is measured

countersinking

is the process of cutting a tapered opening in a hole so that a flathead screw can be installed flush with the workpiece surface

reaming

is the process of finishing a hole to a precise size with a smooth finished surface

spotfacing

is the process of machining a flat spot on a rough surface surrounding a hole opening so that bolts, nuts, and washers will be properly seated when tightened

drilling

is the process of using a cylindrical rotating cutting tool that is sharpened on its end to create a hole

root

is the valley between threads and creates the points from which the minor diameter is measured

tap drill size

the recommended drill bit size for a hole prior to tapping

spot drill

this drill and the center drill are two main types of starter drills

tap extractor

this may be used to remove a broken tap if the tap is somewhat intact

thread series

within a thread system, various diameters and pitch combinations are defined as standard