Tapping Considerations 315

additives

A substance added in small amounts to another substance or material. Additives change or improve a cutting fluid’s abilities to reduce friction and prolong tool life.

alignment

The accurate positioning of machine components. Alignment in tapping generally ensures that the tap and the hole share the same axis or centerline.

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 ends inside the workpiece. Blind holes do not extend through the entire thickness of a workpiece, so they only have one opening.

bottoming taps

A type of tap with a short chamfer that has 1.5 to 2 tapered threads. Bottoming taps are used to cut threads very near the bottom of a blind hole that has very little clearance between the bottom of the hole and the deepest required thread.

carbide

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

chamfer

The portion of the land where the threads are not at full width. Chamfers on a tap progressively increase in size to gradually remove material 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

An amount of space between two objects or components that is necessary to avoid contact. Clearance between the lead of the tap and the bottom of the hole prevents damage to the tap and the workpiece.

CNC

Computer numerical control. A combination of software and hardware that directs the operation of a machine. CNC machines are much more precise than their manual counterparts.

CNC lathe

A computer numerically controlled machine that performs cutting operations on cylindrical parts. CNC lathes can perform precise tapping operations.

CNC mill

A machine tool that uses computer numerical data to control cutting operations on flat, square, or rectangular workpieces. CNC mills can perform precise tapping operations.

coarse threads

Threads with larger pitches. Taps with coarse threads should run at slower speeds than taps with fine threads.

cobalt

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

collet

A slotted device that grips the shank of a tool. Collets are designed to hold tools with specific dimensions.

computer numerical control

CNC. A combination of software and hardware that directs the operation of a machine. CNC machines are much more precise than their manual counterparts.

coolant-fed tap

A tap with a cavity in its center that allows cutting fluid to flow into the hole. A coolant-fed tap, also known as a coolant-through tap, can deliver cutting fluid directly into the hole.

coolant-through tap

A tap with a cavity in its center that allows cutting fluid to flow into the hole. A coolant-through tap, also known as a coolant-fed tap, can deliver cutting fluid directly into the hole.

crests

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

cutting edge

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, or coolant, can improve tool life and finished part quality when used correctly.

cutting speed

The amount of workpiece material a cutting edge contacts in one minute. Cutting speed is measured in surface feet per minute (SFM) or meters per minute (m/min).

drill press

A machine tool that is used for a range of holemaking operations such as drilling, reaming, and tapping. A drill press is limited to only the vertical motion of the spindle to feed the cutting tool into the workpiece.

electrical discharge machining

EDM. A nontraditional machining process that erodes unwanted material from a workpiece using a rapid series of electrical sparks. Electrical discharge machining can be used to remove a tap that has broken inside a hole.

feed

The rate at which a tap moves into a hole. Feed measures how quickly a tap moves in a linear direction.

fine threads

Threads with smaller pitches. Taps with fine threads should run at higher speeds than taps with coarse threads.

floating tapping

A type of toolholding that uses springs to compensate for minor errors in machine setup and operation. Floating tapping is most commonly used on machine tools that are not capable of rigid tapping.

flutes

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

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 leads to a decrease in toughness.

helix angle

The angle formed by the slope of the 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 can be accomplished by drilling, tapping, boring, reaming, or a combination of those operations.

impact resistance

The ability of a material to withstand sudden shock or impact without deforming or breaking. Impact resistance indicates the amount of impact a material can withstand without deforming or breaking.

inch tap

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

inches per minute

ipm. An Imperial measurement that indicates how far in inches a tool advances in one minute. Inches per minute is used to measure feed.

inches per revolution

ipr. An imperial measurement that indicates how far in inches a tool advances in one rotation. Inches per revolution is used to measure feed.

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.

IPR

inches per revolution. An imperial measurement that indicates how far in inches a tool advances in one rotation. Inches per revolution is used to measure feed.

machinability

The relative ease with which material can be removed from a workpiece by machining processes such as cutting or tapping. Machinability depends on the properties of the workpiece material.

machine tool

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.

major diameter

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

manual machine

A machine tool that is operated by the actions of the 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.

manual mill

A machine tool that uses a rotating, multi-point cutting tool to remove material from a workpiece. Manual mills require an operator to control machine movements and adjust settings.

meters per minute

m/min. A metric measurement of cutting speed that describes the distance that a point at the edge of the tap travels as it contacts the workpiece in one minute. Meters per minute depends on both the tap’s major diameter and RPM.

metric tap

A tap measured using the metric system. Metric taps are commonly used in tapping operations, and their key measurements are listed in millimeters.

millimeters per minute

mm/min. A metric measurement that indicates how far in millimeters a tool advances in one minute. Millimeters per minute is used to measure feed.

millimeters per revolution

mm/rev. A metric unit of measurement that indicates how far in millimeters a tool advances in one rotation. Millimeters per revolution is used to measure feed.

minimum full thread depth

The depth to which threads must be cut into a hole to accommodate the intended fastener. Thread depth is determined by the workpiece specifications and is typically at least 1.5 times the tap’s major diameter.

minor diameter

The smallest diameter feature on a tap. Minor diameter is the diameter from root to root on a tap and is typically equal to the diameter of the tap drill.

MM/rev

millimeters per revolution. A metric unit of measurement that indicates how far in millimeters a tool advances in one rotation. Millimeters per revolution is used to measure feed.

modified bottoming taps

A type of tap that has 2-3 tapered threads. Modified bottoming taps, also known as semi-bottoming taps, are commonly used to cut threads in blind holes.

nut

A fastener containing a hole and internal threads that mates with a screw or bolt. A nut may be welded to a broken tap so that you can effectively use a wrench to remove the tap from the hole.

pitch

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

plug taps

A type of tap that has 3.5 to 5 tapered threads. Plug taps are general-purpose taps that can be used in a variety of materials and tapping operations.

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.

rake angle

The angle between the front of the cutting tool and a line that passes through the thread crest and center of a tap. Rake angles affect cutting forces and contact between the tap and workpiece.

relief angle

The angle formed by the slope of the land and a line tangent to the cutting edge of a tap. The relief angle directly follows the cutting edge and reduces tool wear while increasing chip flow.

revolutions per minute

RPM. A unit of measurement that indicates the number of complete rotations a cylindrical component makes in one minute. Revolutions per minute measures spindle speed.

rigid tapping

A type of toolholding that firmly secures the tap in the machine. Most CNC machines are capable of rigid tapping.

roots

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

RPM

revolutions per minute. A unit of measurement that indicates the number of complete rotations a cylindrical component makes in one minute. Revolutions per minute is a measurement of speed.

semi-bottoming taps

A type of tap that has 2-3 tapered threads. Semi-bottoming taps, also known as modified bottoming taps, are commonly used to cut threads in blind holes.

speed

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

spindle speed

The rate at which the machine spindle rotates. Spindle speed is typically measured in revolutions per minute (RPM).

spiral flute tap

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

spiral flute taps

A type of tap with helix-shaped flutes. Spiral flute taps pull chips up and out of the hole.

spiral point taps

A type of tap with straight flutes and an angled cutting face on the first few threads. Spiral point taps are only used on through holes and force chips down through the bottom of the hole.

straight flute taps

A type of tap with flutes parallel to the tap’s centerline. Straight flue taps evacuate chips from either the tap or bottom of a hole and are often used in hand tapping or on materials that create short chips.

surface feet per minute

SFM. An Imperial measurement of cutting speed that describes the distance that a point at the edge of the tap travels as it contacts the workpiece in one minute. Surface feet per minute depends on both the tap’s major diameter and RPM.

synchronizes

To operate at the same time or rate. Synchronized feed and speed allow the machine to create accurate tool movements.

synthetic cutting fluids

A cutting fluid made from water and chemicals, such as nitrites and phosphates. Synthetic fluids are primarily used for their ability to cool.

tap extractor

A tool that grabs the flutes of a broken tap to remove it from inside a hole. Tap extractors are held and turned by a tap wrench.

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.

taper taps

A type of tap that has 7 to 10 tapered threads. Taper taps are often used to tap through holes in particularly hard workpiece materials.

tapping

A metal cutting process that uses a rotating multi-point tool to produce internal threads in a workpiece. Tapping is performed only after first drilling a hole.

tapping center

A machine tool specifically designed to complete high-volume tapping operations. While a tapping machine, also known as a tapping center or tapping press, is not as versatile as other machines, it can complete tapping operations more precisely and more quickly than manual machines.

taps

A cylindrical cutting tool used to produce internal threads in a preexisting 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.

tension-compression holder

A type of toolholder that uses springs to allow the tap to move slightly. A tension-compression holder compensates for minor axial misalignments and can help to prevent taps from breaking.

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 are used to determine pitch on inch taps.

tool geometry

The collective angles formed by the dimensions of a cutting tool that make a tool unique. Tool geometry is an important factor in ensuring taps create accurate internal threads.

tool life

The length of time a cutting tool is expected to be operational before it must be replaced. Tool life can be extended through optimized implementation, including the proper tool geometry, or using 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 to fit different machine tools and cutting tools.

toughness

The ability of a material to absorb energy without breaking or fracturing. Tough cutting tools can withstand sudden stresses but are less hard.

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.

welding

A joining process that uses heat, friction, or a combination of methods to fuse two materials together permanently. Welding can be used to attach a component to a broken tap that you can then grab with a wrench to rotate the tap out of the hole.

workpiece

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