Inspecting a Prismatic Part 321

Functional Gage

A gage representing a worst case mating part that provides a simple pass/fail assessment of the inspected part. Functional gages often can quickly inspect several features at once.

Pythagorean Theorem

A mathematical rule describing how sides of a right triangle are related. The Pythagorean theorem states that the sum of the square of both sides equals the square of the hypotenuse (A² + B² = C²).

Height Gage

A measuring device with a column mounted on a base such as a granite surface plate, a unit that slides up and down, an indicator, and an arm that extends out. Height gages are used to measure vertical and other distances.

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.

Cross-Sectional Dimension

A size dimension that indicates the measurement of a section of a feature that is formed by an intersecting imaginary plane. Also called actual local size, cross-sectional dimensions are often measured with calipers or a micrometer.

Actual Local Size

A size dimension that indicates the measurement of a section of a feature that is formed by an intersecting imaginary plane. Also called cross-sectional dimension, actual local size is often measured with calipers or a micrometer.

Prismatic Part

A solid geometric figure with two end faces that are parallel polygons whose corners are connected by perpendicular lines.

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.

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.

Actual Mating Envelope

AME. A geometrically perfect shape that is a best fit around a feature. AME can be established by inspecting a feature's height with a functional gage, as well as inspecting the feature's cross sectional dimensions.

Coordinate Measuring Machine

CMM. A sophisticated measuring instrument with a flat polished table and a suspended probe that measures parts in three-dimensional space. CMMs can measure using either contact or noncontact methods.

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.

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.

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.

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.

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.

Hypotenuse

The longest side of a right triangle always opposite the 90 degree angle. To find the measurement of a hypotenuse, use the Pythagorean theorem (A² + B² = C²) and solve for C.

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. For an external feature, the VC is the outer boundary. For an internal feature, the VC is the inner boundary.

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.