Introduction to Tapping 275

alignment

The accurate positioning of machine components. Alignment of the tap with the hole is necessary for fasteners to fit correctly.

axis

An imaginary straight line that runs through the center of an object. The axis of a tap is important when determining alignment and positioning.

blind hole

A hole that begins on one side of a workpiece and ends inside the workpiece. Blind holes do not extend through the entire thickness of a workpiece, so they only have one opening.

body

The portion of the tap that enters the workpiece. The body includes the lands and the flutes.

body length

The length from the end of the tap to the highest thread. The body length, also known as the thread length, affects how efficiently a tap can cut threads into a hole.

burrs

A rough edge remaining on material, such as metal, after it has been machined. Burrs may cause injury and lead to poor fit between the hole and fastener.

carbide

A common cutting tool material developed by combining carbon with metals like chromium, tungsten, or titanium. Carbide is used in metal cutting tools for its hardness and wear resistance.

cast iron

An alloy of iron, carbon, and silicon that contains at least 2.0% carbon. Cast iron offers heat resistance and compressive strength.

chamfer

The portion of a land where the threads progressively increase in diameter. Chamfers on a tap remove material gradually and reduce tool wear.

chips

A piece of metal that is removed form a workpiece during a machining operation. Chips are tiny curls, shards, fragments, shavings, or particles of metal.

clearance

A space or distance intentionally left between two objects. Clearance between the tap and the bottom of a blind hole prevents damage to the tap and workpiece.

cobalt

A hard, gray, brittle metal often used to create cutting tools. Cobalt is harder than high-speed steel and tougher than carbide.

computer numerical control

CNC. A programmable system of software and hardware that controls the operation of a machine. Computer numerical control uses mathematical data to execute program instructions and direct the movement of a machine and its components.

coolant

A fluid used to cool , lubricate, and clear chips during a material removal process. Coolant, also known as cutting fluid, can improve tool life and finished part quality when used correctly.

counterboring

The process of cutting a flat-bottomed recess into the opening of a hole. Counterboring provides a space for the head of a flat-faced fastener to rest.

countersinking

The process of cutting a cone-shaped recess into the opening of a hole. Countersinking allows screws to sit flush with a workpiece surface.

crests

The highest point on a thread. The crest size helps determine important thread measurements, such as pitch and diameter.

cutting edges

The leading face of a cutting tool that is in direct contact with the workpiece. The cutting edge performs the actual metal removal during a cutting operation.

cutting fluid

A fluid used to cool, lubricate, and clear chips during a material removal process . Cutting fluid, also known as coolant, can improve tool life and finished part quality when used correctly.

cutting variables

A factor that affects how a cutting tool performs its job. Cutting variables for tapping operations include speed and feed.

drilling

The act of feeding a multi-point cutting tool into a workpiece to create a round hole. Drilling must occur before tapping.

drive square

A square extension at the top end of a tap. The drive square allows a tap to be secured in a machine’s toolholder or in a tap wrench for hand tapping.

drive square size

The width of one side of the tap’s drive square. Drive square size is important when selecting a toolholder for tapping operations.

feed

The rate at which the cutting tool moves into the workpiece. Feed in a tapping operation refers to how quickly the tap moves into the pre-drilled hole and is based on the tap’s pitch.

flush

In line and level with another surface. Countersinks allow space for fasteners to be flush with workpiece surfaces.

flutes

A straight or helical recessed feature on the periphery of a tap. Flutes allow chips to evacuate the hole.

forming taps

A type of tap that creates threads by compressing the material rather than removing it. Forming taps create no chips and are often used on softer metals.

friction

The resistance between the contact surfaces of two objects. Friction generates heat and increases the wear between components.

hand tapping

A type of benchwork operation that involves manually cutting an internal thread. Hand tapping is performed without the use of a machine tool.

hardness

A material’s ability to resist indentation or scratching. An increase in hardness generally lead to a decrease in toughness.

heels

The edge of a tap’s lands opposite the cutting edge. The heel plays an important role in reducing friction and prolonging tool life.

helix angle

The angle formed by the edge of a flute and the tap’s axis. Larger helix angles are better suited for softer materials and smaller helix angles are better suited for harder materials.

high-speed steel

HSS. A category of tool steels used for cutting tool applications. High-speed steel is a tough but inexpensive material.

holemaking

A machining operation that creates, shapes, or finishes a hole. Holemaking encompasses a number of operations, including drilling, boring, reaming, and tapping.

Imperial System

A system of measurement used primarily in the United States, the United Kingdom, Myanmar, and Liberia. The Imperial System uses inches and feet to measure distance.

inch taps

A tap measured using the Imperial System. Inch taps are commonly used in tapping operations, and their key measurements are listed in inches.

inner diameter

ID. The interior surface of a workpiece hole or other feature. Inner diameter operations include drilling and tapping.

internal threads

A type of thread that spirals around the interior of a hole. Internal threads engage with fasteners to hold two or more components together.

lands

The threaded area of a tap between the flutes. The lands are the portion of the tap that contact the workpiece to remove material.

machine tools

A power-driven machine that is used to manufacture parts by guiding a tool to shape workpieces. Common examples of machine tools include the drill press, the lathe, and the mill.

machining

A subtractive manufacturing process that involves removing material to form an object. Machining includes methods that remove metal using cutting tools, such as milling, turning, and drilling.

major diameter

The largest diameter of a threaded feature. Major diameter is the diameter from crest to crest on a tap.

manual machine

A machine tool that is operated by the actions of a machine operator, rather than by automated or computerized actions. Manual machines are less expensive than computer numerical control (CNC) machines but also less precise and efficient.

metric taps

A tap measured using the metric system. Metric taps' key measurements are listed in millimeters.

minor diameter

The smallest diameter of a threaded feature. Minor diameter is the diameter from root to root on a tap.

multi-point cutting tool

A cutting tool that has two or more cutting edges. Multi-point cutting tools used in holemaking include drills, reamers, and taps.

overall length

The length from one end of the tap to the other. Overall length is an important factor in deciding the correct tap for a tapping operation.

parallel

A line or object that is equidistant from another line or object at all points along their length. Parallel lines never intersect with each other.

peck tapping

A tapping technique that periodically retracts the tool to clear chips or flood the hole with cutting fluid. Peck tapping is often used when tapping blind holes.

pitch

The distance between corresponding points on consecutive threads. Pitch can be determined by measuring the distance between two adjacent crests or roots.

pitch diameter

The diameter of a threaded part at the point where the size of the threads and the size of the spaces between threads is equal. Pitch diameter is larger than the minor diameter but smaller than the major diameter.

powdered metal

A type of tool material created by applying heat and pressure to metal powder. Powdered metal tools are more resistant to wear than high-speed steel.

roots

The lowest point on a thread. The root size helps determine important thread measurements, such as pitch and diameter.

screw

An externally threaded cylindrical fastener with a head and a flat or pointed threaded end opposite the head. Screws are designed to fit into threaded holes.

shank

The cylindrical part of a tap above the cutting edges. Shanks include markings that indicate the tap’s size and measurements.

shank diameter

The width of a tap’s shank. The shank diameter is slightly smaller than the tap’s major diameter.

speed

The rate at which a workpiece and cutting move past one another at their point of contact. Speed in a tapping operation refers to how quickly the tap or workpiece rotates.

spiral flute tap

A type of tap with helix-shaped flutes. A spiral flute tap pulls chips up and out of the hole.

spiral point tap

A type of tap with straight flutes and an angled cutting face on the first few threads. A spiral point tap is only used on through holes and forces chips down through the bottom of the hole.

straight flute tap

A type of tap with flutes parallel to the tap’s axis. A straight flute tap is often used in hand tapping and can evacuate chips from either the top or bottom of a hole.

tap

A cylindrical cutting tool used to produce internal threads in a pre-existing hole. A tap, sometimes called a thread tap, has thread forms on its outer surface that match the internal threads it is designed to produce.

tap collet

A slotted workholding device that grips the drive square and shank of a tap. A tap collet fits into the machine’s toolholder and is designed to hold a tap with specific dimensions.

tap drill chart

A table that lists various tap sizes and their corresponding tap drill sizes. A tap drill chart serves as a reference to help operators determine appropriate tap drill sizes when drilling a hole before tapping.

tap drill size

The size of the drill required to create a specific threaded hole. Tap drill size determines the size of the hole before tapping.

tap wrench

A manual tool that is used during hand tapping. Tap wrenches hold a hand tap’s square end and shank to allow a machinist to turn it.

tapping

A metal cutting process that uses a rotating multi-point tool to produce internal threads in a workpiece. Tapping is required for holes to fit threaded fasteners or mating parts.

thread length

The length from the end of the tap to the highest thread. The thread length, also known as the body length, affects how efficiently a tap can cut threads into a hole.

thread relief

The thinning of the thread from the cutting edge to the heel. Thread relief allows space between the tap and the workpiece to reduce friction and extend tool life.

thread tap

A cylindrical cutting tool used to produce internal threads in a preexisting hole. A thread tap, usually called a tap, has thread forms on its outer surface that match the internal threads it is designed to produce.

threaded fastener

A device that uses compatible threads to hold two or more objects together. Threaded fasteners include screws, bolts, and nuts.

threads per inch

TPI. The number of threads along the tap within one inch. Threads per inch is used to determine appropriate drill and tap sizes.

through hole

A hole that begins on one side of a workpiece, extends through it, and exits on another side. Through holes have openings on both sides.

tool life

The length of time a cutting tool is expected to be operational before it must be replaced. Tool life can be extended by using the proper tool geometry and cutting fluids.

tool wear

The erosion of tool material as a result of friction. Tool wear degrades the accuracy and precision of a tool.

toolholder

A device used to hold a cutting tool in place. Toolholders come in a variety of shapes and sizes, but more rigid ones are required when using hard cutting tools.

toughness

The ability of a material to absorb energy without breaking or fracturing. Cutting tools with high toughness can withstand sudden stresses but are often less hard.

TPI

Threads per inch. The number of threads along the tap within one inch. Threads per inch is used to determine appropriate drill and tap sizes.

wear resistance

A material’s ability to resist the gradual wearing away caused by abrasion and friction. Increased wear resistance can lengthen the life of a tap.

workpiece

A material being machined or undergoing another type of processing. Workpiece material is an important factor in deciding the correct tap for a tapping operation.