NIMS Core Turning Skills 132

accuracy

The difference between a measurement reading and the true value of that measurement. The less error present in the measurement, the more accurate the results.

boring

The use of a single-point cutting tool to enlarge an existing hole. Boring operations, which are programmed in sfm (m/min), help to create a hole that is concentric and that meets tight tolerances.

catastrophic tool failure

The sudden and complete loss of tool performance. Catastrophic tool failure can be the result of gradual degradation and intermittent failure.

centerline

An imaginary line that runs through the center of a cylindrical workpiece and around which the workpiece rotates. Centerlines are at a 90° angle to a lathe's headstock.

circular runout

A two-dimensional geometric tolerance that controls the form, orientation, and location of multiple cross sections of a cylindrical part as it rotates. Circular runout is a related tolerance.

circularity

A two-dimensional form tolerance that describes the allowable variability in the shape and appearance of a circle. Also known as roundness, circularity is an individual tolerance.

concentricity

A three-dimensional locational tolerance that describes the location of opposing points in cylindrical features with respect to a datum reference. Concentricity is a related tolerance.

constant

A variable or number that does not change value. The English constant 3.82 or the metric constant 318.3 is used in lathe speed conversion formulas.

constant surface speed

CSS. A setting on a CNC lathe that adjusts the spindle rpm as the tool travels toward and away from the spindle's axis. Constant surface speed keeps surface feet per minute (m/min) consistent.

cross section

A section of a feature that is formed by an intersecting imaginary plane. Any two-dimensional cross section of a feature should remain within two imaginary concentric circles to have circularity.

cutting

The use of single- or multi-point tools to separate metal from a workpiece in the form of chips. Cutting processes vary based on the requirements of a finished part.

cylindricity

A three-dimensional form tolerance that describes the allowable variability in the shape and appearance of a cylinder. Cylindricity is an individual tolerance.

dial indicator

A measuring instrument with a contact point attached to a spindle and gears that move a pointer on the dial. Two opposing dial indicators can be used to measure the concentricity of a cylindrical feature.

diameter

d. The distance from one edge of a circle to the opposite edge that passes through the center. Diameter measurements are required with round or cylindrical features.

drilling

Using a multi-point tool to machine a new round hole into the surface of a workpiece. Drilling operations, which require a constant rpm, can be done on a drill press, lathe, or mill.

facing

A turning operation that removes material from the end of the rotating cylindrical part. Facing operations, which are programmed in sfm (m/min), are usually performed to establish a part's length.

feed

The rate that the cutting tool travels along the length of the workpiece. Feed measures a linear movement.

geometric dimensioning and tolerancing

GD&T. An international standard for communicating instructions about the design and manufacturing of parts. GD&T uses universal symbols and emphasizes the function of the part.

inches per minute

ipm. The distance in inches that the entire tool advances in one minute. Inches per minute is a measurement of feed of a rotating cutting tool on the lathe.

inches per revolution

ipr. The distance in inches that the tool advances during one complete revolution of the workpiece. Inches per revolution is a measurement of feed on the lathe.

insert pockets

An interior recess on a toolholder into which cutting inserts are affixed. Insert pockets must be free of chips and scratches that could cause the insert to sit uneven in the pocket.

ipr

Inch per revolution. The distance in inches that the tool advances during one complete revolution of the workpiece. Inch per revolution is a measurement of feed on the lathe.

lathe

A machine tool that is used to produce a range of cylindrical workpieces. On a basic lathe, the part rotates in a spindle while the cutting tool is guided along its exterior diameter or into the part to create a hole located on the part's centerline.

live tooling

Rotating power-driven cutting tools, such as end mills and drills, that are held in the turret of a lathe. Live tooling can perform machining operations off the part centerline while the workpiece is held stationary in the spindle.

lobing

Deviation from workpiece roundness. Circularity, cylindricity, and runout all restrict lobing on a cylindrical part.

m/min

Surface meters per minute. The distance in meters that the workpiece surface travels in one minute. Surface meters per minute, which is a metric measurement for speed, depends on workpiece size and rpm.

maximum material condition

MMC. The point at which a feature contains the greatest amount of material within its acceptable size limit. The smallest acceptable hole and the largest acceptable shaft are examples of MMC.

millimeters per minute

mm/min. The distance in millimeters that the entire tool advances in one minute. Millimeters per minute is a metric measurement for feed of a rotating cutting tool on the lathe.

millimeters per revolution

mm/rev. The distance in millimeters that the tool advances during one complete revolution of the workpiece. Millimeters per revolution is a metric measurement for feed on the lathe.

milling

A cutting operation in which a rotating multi-point cutting tool is fed along a part's surface to remove material. Milling operations are very versatile and generally produce flat surfaces.

mm/rev

Millimeter per revolution. The distance in millimeters that the tool advances during one complete revolution of the workpiece. Millimeters per revolution is a metric measurement for feed on the lathe.

off-center drilling

A holemaking process that makes a round hole at any location on a part that deviates from the part's centerline. Off-center drilling can sometimes be performed on a lathe with live tooling.

pi

A special constant value that relates the diameter of a circle to its circumference. Pi is roughly 3.14 and is used to find the circumference and area of a circle.

position

A three-dimensional geometric tolerance that controls how much the location of a feature can deviate from its true position. Position is a related tolerance.

regardless of feature size

RFS. A modifier indicating that the stated tolerance for a feature applies regardless of its actual size within an acceptable size limit. If RFS controls a location being inspected for position, that location should be inspected with a variable gage.

revolutions per minute

rpm. The number of revolutions that a spindle or cutting tool completes in one minute. Revolutions per minute is a measurement of speed in both English and metric systems.

roundness machine

A sophisticated inspection device with a precision spindle that measures various circular and cylindrical features. A roundness machine is necessary for inspecting such tolerances as circularity, cylindricity, circular runout, and total runout.

rpm

Revolutions per minute. The number of revolutions that a spindle or cutting tool completes in one minute. Revolutions per minute is a measurement of speed in both English and metric systems.

sfm

Surface feet per minute. The distance in feet that the workpiece surface travels in one minute. Surface feet per minute, which is an English measurement for speed, depends on workpiece size and rpm.

speed

The rate that the workpiece surface and cutting tool pass each other at the point of contact. Speed on a lathe refers to the rotation of the workpiece in the spindle.

surface feet per minute

sfm. The distance in feet that the workpiece surface travels in one minute. Surface feet per minute, which is an English measurement for speed, depends on workpiece size and rpm.

surface meters per minute

m/min. The distance in meters that the workpiece surface travels in one minute. Surface meters per minute, which is a metric measurement for speed, depends on workpiece size and rpm.

threading

The process of cutting a long, spiraling groove into a workpiece with a single-point tool. Threading operations, which require a constant rpm, are essential for the creation of fasteners.

tolerance zone

An imaginary zone in which a part feature must be completely contained for the part to pass inspection. The tolerance zone contains the dimensions between the maximum and minimum limits of a feature's location.

tool crib attendant

A worker whose job involves the inventory of cutting tools. Tool crib attendants inspect tools for damage, store them for later use, and distribute them as needed.

tool life

The length of time that a cutting tool can function properly before it begins to fail. Tool life is affected by several different cutting variables.

total indicator reading

TIR. The absolute value of the total deviation of a dial indicator's movement. TIR is calculated to inspect the total runout of a cylindrical part or the flatness of a prismatic part.

total runout

A three-dimensional geometric tolerance that controls the form, orientation, and location of the entire length of a cylindrical part as it rotates. Total runout is a related tolerance.

turning

A machining operation that rotates a cylindrical workpiece while a single-point tool is guided along the length of the part. Turning operations are performed on a lathe and are programmed in sfm (m/min).

turning

A machining operation that rotates a cylindrical workpiece while a single-point tool is guided along the length of the part. Turning operations are performed on a lathe and programmed in surface feet per minute (sfm) or meters per minute (m/min).

visual inspection

A visual assessment of surface defects. Visual inspection involves closely examining with the naked eye to check for defects.