NIMS Core Milling Skills 131

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.

angularity

A three-dimensional orientation tolerance that describes the allowable variability in the angular relationship between a surface and a datum. Angularity is a related tolerance.

CAD

Computer-aided design. A computer software program that aids in the automated design and technical precision drawing of a part, product, process, or building. A CAD model can be used like a part drawing.

chatter

The development of surface imperfections on a workpiece caused by cutting tool vibration. Chatter is more likely to occur in tools with an extend out of holder that is more than eight times the length of the length of cut and more than twelve times the overall length of the tool.

chip load

The linear distance traveled by the cutter during the engagement of a single cutting tooth. Chip load, which is also known as feed per tooth (fpt), is the feed measurement for multiple cutting edge tools.

constant

A variable or number that does not change value. The constant 3.82 (318.3) is used in the formula machinists use to convert mill speed from surface feet (meters) per minute to revolutions per minute.

cutting edge

The edge of a cutting tool that engages the workpiece material and removes material in the form of chips. A tool may have a single cutting edge or multiple cutting edges.

cutting tool

A device with one or more edges that is designed to cut metal. Cutting tools are often designed to be used on a machine such as a mill or lathe.

deflection

The unintended movement or repositioning of a component due to a mechanical force. Deflection of a cutting tool can cause poor surface finish and inaccurate dimensions.

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 flatness, profile of a surface, angularity, and parallelism of a prismatic part.

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.

extend out of holder

EOH. The length of tool that extends from the end of a toolholder. The extend out of holder, or overhang, should be no more than eight times the length of the length of cut and no more than twelve times the overall length of the tool.

feed

The rate at which the cutting tool travels along the length of the workpiece. Feed measures linear movement.

feed per revolution

fpr. The linear distance that a tool advances during one rotation of the workpiece or cutting tool. On the mill, feed per revolution may be used to convert feed per tooth (fpt) to either inches per minute (ipm) or millimeters per minute (mm/min).

feed per tooth

fpt. The linear distance traveled by the cutter during the engagement of a single cutting tooth. Feed per tooth, which is also known as chip load, is the feed measurement for multiple cutting edge tools.

flatness

A three-dimensional form tolerance that describes the allowable variability in the shape and appearance of a surface that lies in a plane. Flatness is an individual tolerance.

flutes

A groove on the periphery of a cutter that provides room for chips to flow away from the cut. Flutes are present on mills along the length of cut.

fpr

Feed per revolution. The linear distance that a tool advances during one rotation of the workpiece or cutting tool. On the mill, fpr may be used to convert feed per tooth (fpt) to either inches per minute (ipm) or millimeters per minute (mm/min).

fpt

Feed per tooth. The linear distance traveled by the cutter during the engagement of a single cutting tooth. Feed per tooth, which is also known as chip load, is the feed measurement for multiple cutting edge tools.

gage wire

Wire of a standardized diameter length that is used to measure part features during inspection. Gage wire is used to inspect the straightness, profile of a line, and perpendicularity of a prismatic part.

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.

in./tooth

Inches per tooth. A unit of measurement for feed that indicates the amount of material removed by each tooth of a cutting tool. Inches per tooth is the English unit of measurement for feed per tooth.

inches per minute

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

inches per tooth

in./tooth. A unit of measurement for feed that indicates the amount of material removed by each tooth of a cutting tool. Inches per tooth is the English unit of measurement for feed per tooth.

insert

A replaceable cutting tool with a geometric shape that has multiple cutting surfaces and is mechanically held in a toolholder. Inserts must sit flat in the insert pockets of a toolholder when properly installed.

insert pockets

An interior recess on a milling holder 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.

ipm

Inches per minute. The distance in inches that the entire tool advances in one minute. Inches per minute is an English measurement of feed for a rotating cutting tool on the mill.

length below shank

LBS. The axial measurement of the parts of a tool excluding the shank. Length below shank includes the lengths of both the neck and length of cut.

length of cut

LOC. The axial measurement of a cutting tool's flutes. The length of cut should be a minimum of one-eighth of the tool's extend out of holder.

m/min

Surface meters per minute. The distance in meters that the cutting surface travels in one minute. Surface meters per minute, which is a metric measurement of speed, depends on both cutting tool 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 maximum material condition.

meters per minute

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

mill

A machine that uses a rotating multi-point tool to remove metal from the surface of a workpiece. Mills may be operated either manually or by computer numerical control (CNC).

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 mill.

millimeters per tooth

mm/tooth. A unit of measurement for feed that indicates the amount of material removed by each tooth of a cutting tool. Millimeters per tooth is the metric unit of measurement for feed per tooth.

mm/min

Millimeters per minute. 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 mill.

mm/tooth

Millimeters per tooth. A unit of measurement for feed that indicates the amount of material removed by each tooth of a cutting tool. Millimeters per tooth is the metric unit of measurement for feed per tooth.

neck

The section of a cutting tool that separates the flutes from the shank. The neck of a tool allows chips to evacuate more effectively than tools without necks.

overall length

OAL. The entire axial measurement of a cutting tool. The overall length of a tool includes its shank, cutting edge, and neck, if it has one.

overhang

The length of tool that extends from the end of a toolholder. The overhang, or extend out of holder, should be no more than eight times the length of the length of cut and no more than twelve times the overall length of the tool.

parallelism

A three-dimensional orientation tolerance that describes the equal distance between pairs of points, lines, or planes. Parallelism is a related tolerance.

perpendicularity

A three-dimensional orientation tolerance that describes the allowable variability in the 90° angular relationship between a surface and a datum. Perpendicularity is a related tolerance.

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.

precision square

An L-shaped tool that forms a 90° angle. Precision squares are used to inspect the perpendicularity of one surface in comparison with another.

profile of a line

A two-dimensional profile tolerance that describes the allowable variability in the contour of the edge seen in the section view. Profile of a line can be either an individual or a related tolerance.

profile of a surface

A three-dimensional profile tolerance that describes the allowable variability in the contour of a surface. Profile of a surface can be either an individual or 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 the location is controlled regardless of feature size, it 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 the English and metric systems.

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 the English and metric systems.

sfm

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

shank

A cylindrical part of a tool or device opposite the cutting edge. The shank is the part of a cutting tool that is held in the toolholder.

sine bar

A measuring device used to measure angles. A sine bar is a steel bar with matching cylinders at each end set up at various angles for the machining and inspection of parts.

speed

The rate at which the workpiece surface and cutting tool pass each other at the point of contact. Speed for a mill refers to the rotation of the cutting tool on the spindle.

spindle

The part of the machine tool that spins. On the mill, the spindle holds the cutting tool.

straightness

A two-dimensional form tolerance that describes allowable variability in the shape and appearance of a line in a section view. Straightness is an individual tolerance.

surface feet per minute

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

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.

toolholder

A mechanism used to rigidly hold a cutting tool in place during machining. Toolholders are classified so that they can be paired with the correct style of cutting tool or insert.

total indicator reading

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

true position

The imaginary perfect position of a feature described by the design specifications. The location of a feature's true position is determined by the positional tolerance.

true profile

The perfect, imaginary profile described by the design specifications. The profile tolerances compare the actual profile of a feature to the true profile.

virtual condition

VC. A constant worst case imaginary boundary used when parts are toleranced for assembly that is defined by the collective effects of a feature's size and geometric tolerance. The virtual condition for an external feature is the outer boundary, and the virtual condition for an internal feature is the inner boundary.

visual inspection

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

workholding

A device used to hold and locate a workpiece. Workholding is used to keep the workpiece stationary on a mill.