Interpreting Prints 231

angles

A shape formed by two intersecting lines or planes. Angles are measured in degrees.

arc

The round or curved feature of a part depicted on a print. Arcs are measured as if they were part of an imaginary circle.

arm

A long appendage that allows a mechanical device to reach for parts and other components. An arm on a CMM holds the probe.

automatic edge detection

A method of edge detection that uses an electronic or fiber-optic device to locate differences between light and dark areas. Automatic edge detection can be provided by an external or internal device on an optical comparator.

auxiliary view

A print view that rotates a part at a right angle to an angled feature of a part. Auxiliary views provide a full straight-on picture of the angled side that cannot be fully represented with a basic orthographic view.

average roughness

Ra. The average distance between the peaks and valleys that characterize a particular surface. Average roughness describes the quality of a surface but does not indicate waviness or flaws.

beveled

Angled in comparison to the major surfaces of a part. Beveled surfaces include chamfers.

blind holes

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

blueprints

A document containing all the information necessary to manufacture and inspect a part. A blueprint is also known as a print or an engineering drawing.

bore gages

A hole inspection gage that makes three points of contact with the inside of the hole. Bore gages can provide diameter and depth measurements.

calipers

A measuring instrument with a pair of jaws on one end and a long beam containing a marked scale of unit divisions on the other. Calipers are adjusted to fit around a part to measure the length and diameter of a feature or placed inside a hole to measure the hole's diameter.

callout

The listed designations for a specific thread. The callouts for Unified threads and metric threads include information relating to nominal size, pitch, fit, type of thread, and other specifications.

Cartesian coordinate system

A positioning system that uses three perpendicular linear axes to describe the location of an object in three-dimensional space. The three linear axes in the Cartesian coordinate system are the X axis, Y axis, and Z axis.

centerpoint

A single imaginary point located an equal distance from all of the points on the exterior of a circular feature. The centerpoint of a circle is shown as a small cross on prints.

chamfer gages

A handheld measuring device with three angled plungers on one end and a dial on the other. Chamfer gages measure the largest diameter of a countersink or counterbore.

chamfers

An angled surface added to an edge of a workpiece. Chamfers replace a sharp edge with a beveled surface.

circumference

The boundary or perimeter around a circle. The circumference measures the distance around a circle.

class of fit

A designation that indicates how loose or tight a Unified thread should fit. Class of fit uses numbers to designate tightness, with higher numbers being the tightest.

CMM

Coordinate measuring machine. A sophisticated measuring instrument with a flat, polished table and a suspended probe that inspects parts in three-dimensional space. A CMM can operate using either contact or noncontact methods.

concave

Curving inward, like the interior surface of a bowl. Concave corners form interior corner radii.

controlled radius

A radius that yields a circle, arc, or sphere with no flat sections or reversals. In prints, a controlled radius is indicated with the symbol "CR."

convex

Curving outward, like the exterior of a circle or sphere. Convex corners form exterior edge radii.

coordinate measuring machine

CMM. A sophisticated measuring instrument with a flat, polished table and a suspended probe that inspects parts in three-dimensional space. A coordinate measuring machine can operate using either contact or noncontact methods.

corner radius

An arc that forms a rounded corner. A corner radius can be an interior corner radius or an exterior edge radius.

corners

A part feature formed by the meeting of two or more planes. Corners are common angled part features, often creating right angles.

counterbores

A flat-bottomed recess added to the opening of a hole. Counterbores allow the head of a flat-faced fastener to sit inside the hole.

countersink gages

A handheld measuring device with a conical plunger on one end and a dial on the other. A countersink gage is used to measure the diameter of a countersink or counterbore.

countersinks

A cone-shaped recess added to the opening of a hole. Countersinks allow a tapered fastener head to fit inside the hole.

crest

The top or peak of a thread. The crest is formed by the meeting of two flanks.

degrees

A unit of measurement used to indicate the size of an angle. Degrees are represented by a small circle positioned above and to the right of a number.

depth micrometer

A type of micrometer that has a spindle perpendicular to a flat base. Depth micrometers are primarily used to measure the depth of holes.

dial

A meter on the end of an inspection instrument that consists of numeric measurements in a circle and a pointer. Chamfer gages and countersink gages feature dials.

diameter

The distance from one edge of a circle to the opposite edge, as measured through the center of the circle. The diameter of a circle is two times its radius.

dimensions

The measurements of a part or part feature. Dimensions typically include length, width, and height.

engineering drawings

A document containing all the information necessary to manufacture and inspect a part. An engineering drawing is also known as a print or a blueprint.

exterior edge radius

A rounded corner located where two features meet on the exterior of a part. An exterior corner radius is measured as if it was part of an imaginary circle.

fastener

A device that holds objects together or locates them in relation to one another. Common fasteners include screws and bolts.

features

A defining physical characteristic of a part. Features include corners, edges, holes, and grooves.

fingernail test

A method of inspecting surface finish by scraping a fingernail across the surface of a machined part and then across a surface replica block to compare roughness. A fingernail test is a type of comparison measurement.

finishing

A final process performed on a part. Finishing processes include cleaning, final sizing, polishing, and applying coatings.

flank

An angled side of a thread that connects the root to the crest. Flanks occur in pairs.

go/no-go gage

An instrument with an established standard size that determines whether a part feature passes or fails inspection. Go/no-go gages do not provide measurements.

inside diameter

ID. A spiraling ridge on the interior of a part or hole. Inside diameter threads are designed to mate with outside diameter threads.

inside micrometer

A type of micrometer that is placed in a hole to measure its inside diameter. An inside micrometer is primarily used to measure holes but can sometimes be used to measure hole features, such as counterbores and spotfaces.

inspection

The examination of a product during or after its creation to confirm that it adheres to specifications. Inspection allows manufacturers to identify and correct product defects.

interior corner radius

A rounded corner located where two features meet on the interior of a part. An interior corner radius is measured as if it was part of an imaginary circle.

jaws

Movable components that allow a device to open and close around an object. Calipers have jaws that can measure hole diameter.

material removal allowance

The amount of stock to be removed from a part in inches or millimeters. Material removal allowance is indicated by a number to the left of a material removal required symbol.

mating part

The object that a workpiece has been manufactured to fit. Nuts and bolts are mating parts.

metric thread standard

A system for cataloging and defining threads based on millimeters. The metric thread standard was developed in Europe by the International Organization for Standardization (ISO), and is also known as the ISO metric thread standard.

microinches

μin. A unit of measurement that is equal to one-millionth (0.000001) of an inch. Microinches are typically used to measure average roughness in the English system.

micrometers

µm. A unit of measurement that is equal to one-millionth (0.000001) of the metric standard meter. Micrometers are typically used to measure average roughness in the metric system.

micrometers

A measuring instrument with a threaded spindle that slowly advances to close in around or on a part. The typical micrometer is accurate within 0.002 in. (0.02 mm).

nominal diameter

The overall diameter of the fastener, which may be different from its actual, measurable size. Nominal diameter is used to indicate a fastener's nominal size in metric and Unified thread specifications.

optical comparator

A sophisticated measuring instrument that projects an image of a part onto a screen so that the shape, size, and location of its features can be compared to measurement markings. Optical comparators can be used to inspect both surface and profile features in two dimensions.

out-of-round

Irregularly shaped or not totally round. A bore gage can determine whether a hole is out-of-round.

outside diameter

OD. A spiraling ridge on the exterior of a part. Outside diameter threads are designed to mate with an inside diameter thread.

overlay chart

A circular piece of transparent material that contains fine measurement markings for use on an optical comparator. Overlay charts are placed directly on top of the viewing screen.

peaks

The point of maximum height on the surface of a part. The distance between peaks and valleys determines average roughness.

perpendicular

Forming a right angle with another line, plane, or object. Perpendicular lines intersect one another at a 90-degree angle.

pictorial method

A method of visually representing threaded features on prints that uses a realistic illustration. The pictorial method uses a drawing of the actual thread to represent the thread.

pin gages

A small cylindrical device made of hardened metal used to inspect hole diameter. Pin gages come in a set of various sizes.

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 an imaginary cylinder that passes through the threaded feature so that it intersects the thread groove and the thread ridge equally. Pitch diameter marks the theoretical point where threads of a fastener and threads of a hole meet.

planes

A flat, level surface. When two planes intersect, they form an angle.

plug gages

A cylindrical device made of hardened metal used to inspect hole diameter. Plug gages come in a set of various sizes.

plunger

A component of a measuring instrument that is pressed against a part to record a reading. When pressed, the plunger is pushed inside the base of the measuring instrument.

points of tangency

The point on a circle where a tangent plane or line touches it. The points of tangency help define rounded features in prints.

prints

A document containing all the information necessary to manufacture and inspect a part. A print is also known as a blueprint or an engineering drawing.

probe

A device on an inspection instrument that gathers measurement data from the workpiece. The probe on a CMM uses either contact or noncontact methods.

profilometer

An inspection device that uses a stylus to trace along the surface of a part to collect quantifiable inspection data. Profilometers determine the average amount of roughness on a surface.

radius

The distance between the center of a circle and a point on its circumference. The radius is always half the length of the diameter.

radius gage

An inspection device with round edges of a known radius used to inspect rounded features. Radius gages come in sets with different radius sizes.

reversals

A portion of the surface of a rounded feature that curves slightly in the opposite direction of the curve, creating an uneven surface. Reversals are not permitted in controlled radii.

right angle

An angle that measures exactly 90 degrees. A right angle is formed by two perpendicular lines or planes.

robot

A mechanical device that can be programmed to perform a variety of complicated, repetitive tasks. Robots are used to automate manufacturing and inspection processes.

root

The groove at the base or bottom of a thread. The root is formed by the meeting of two flanks.

schematic method

A method of symbolically representing threaded features on prints that uses a series of parallel lines. The schematic method uses thick lines to represent roots and thin, short lines to represent crests.

screen ring

A set of circular markings around the perimeter of an optical comparator's viewing screen that indicate angle measurements in half-degree increments. Screen rings are used to inspect angled features on parts.

screw pitch gage

An inspection device with an edge that has symmetrical points used to inspect the pitch of threads. Screw pitch gages come in sets of different pitches.

sensitivity

The smallest change in a measurement that an instrument is capable of detecting. Instruments with greater sensitivity provide more exact readings.

simplified method

A method of symbolically representing threaded features on prints that uses dashed lines to represent crests and roots. The simplified method is the most common method of representing threads in prints.

sine bar

A steel bar with matching cylinders on either end that is used to precisely measure angles. One end of a sine bar is placed at a specific height to position the sine bar at a known angle.

spotfaces

A shallow flat-bottomed recess added to the opening of a hole. Spotfaces allow the head of a flat-faced fastener to sit evenly against the workpiece surface.

stylus

The precision-tip of an inspection device that records measurements. The stylus of a profilometer detects the peaks and valleys of a surface to determine average roughness.

surface finish

The degree of roughness and variation on the surface of a part after it has been manufactured. Surface finish is often described by the lay, roughness, and waviness remaining on a part.

surface replica blocks

A set of metal blocks, each of which are ground to a specific standard roughness pattern. Surface replica blocks are used in comparison measurements.

symmetrical

Having completely identical features on either side of a point, line, or plane. Both sides of a symmetrical object have the same dimensions.

tangent

Touching a circle at exactly one point. Rounded features have two or more flat surfaces that are tangent to them.

tapers

A part feature that gradually increases or decreases in size at an angle. Tapers are common angled part features.

thread plug gage

A hardened, cylindrical gage with threads used to inspect the fit of internal threads. Thread plug gages are available in standardized sizes.

thread ring gage

A disk of heavy metal with a central, threaded hole made to match a particular external thread. A thread ring gage is screwed onto the part being inspected as though the two were mating parts.

threads

A raised, spiraling ridge around the exterior or interior of a cylindrical object. Threads are used to fasten or provide motion between parts.

threads per inch

TPI. The number of threads that occur in one linear inch. Threads per inch is used to indicate thread pitch in Unified thread specifications.

through holes

A hole that passes completely through a workpiece from one side to another. Through holes can be seen from both sides or ends of the workpiece.

tolerance

An unwanted but acceptable variation or deviation from a desired dimension. A dimension that is within tolerance meets specifications.

tolerance zone

An imaginary zone in which a part feature must be completely contained for the part to pass inspection. The tolerance zone of a rounded feature is represented on a print by an arc and the dimensions of the feature's maximum measurements and minimum measurements.

touch test

A method of inspecting surface finish by running a finger across the surface of a machined part and then across a surface replica block to compare roughness. A touch test is a type of comparison measurement.

trigonometry

The branch of mathematics that addresses the measurements of and relationships between a triangle and its parts. Trigonometry is necessary for calculating part angles with sine bars.

Unified thread standard

UN. A system for cataloging and defining threads based on inches. The Unified thread standard was developed by the United States, Canada, and the United Kingdom.

valleys

The point of maximum depth on the surface of a part. The distance between valleys and peaks determines average roughness.

views

A drawing that consists of all the lines necessary to illustrate the shape of a part. A print often contains multiple views to convey all of a part's design elements.

X-Y coordinate grid

A numerical grid used to describe the location of an object in two-dimensional space. An X-Y coordinate grid expresses measurements as the distance from a point to the fixed location where two linear axes intersect.