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Glossary of Terms


Air Bearing Handbook

Air Film Thickness

Thickness of the pressurized air film between the bearing face & guide way. (The film is just another way to address the pressurized air) Pressurized boundary layer or air beneath an air bearing between surface that allows non-contact of bearing and surface.


American Society of Mechanical Engineering.


American Society of Precision Engineering.


Having a common center. Round items sharing the same center or axis, as in rotation.


The state of being concentric, conformance to a common center. Ex: The inner and outer walls of a tub are concentric to each other. Condition in which 2 or more (cylinders, cones, spheres) in any combination have a common axis.

CQT Book

A handbook that helps prepare for the ASQ Certified Technician Exam, providing a comprehensive set of training tools.


(from answers.com) The capacity built into a mechanical or electrical device to prevent excessive correction and the resulting instability or oscillatory conditions. -An energy absorbing function minimizing oscillation or vibrations. (From Drew) see pre-load.


Excursion from a perfect motion, deviation from perfect. (There are actually different types of error motion, such as cylindrical or a straight line that has a bow. The bow in a straight line would be the error motion. And any deviation from a perfect circle would be the error in that case.)


Cannot have a deviation over certain length, deviation in surface parallelism over a pressurized distance.

Fly Height

Thickness of air bearing film between the bearings face & guide way. New Way Air Bearings fly at 5 microns or .0002” (2/10ths)

GD & T

(def from engineer’s edge) – Geometric dimensioning and tolerance is a language used on mechanical engineering drawings composed of symbols that are used to efficiently and accurately communicate geometry requirements for associated features on components and assemblies.


(def from A Dictionary of Units of Measurement from University of North Carolina at Chapel Hill) – A metric unit of distance equal to one millionth of a meter or .000001. “Micron” is simply a shorter name for the micrometer. In 1968 the CGPM decided to drop the micron as an approved unit and recommend that micrometers be used instead. Microns, however, are still in common use. 1 nm = 40 millionths of an inch.

Nano Postitioning

Nanometor level tolerance.


An open space allowing passage. Usually denotes a smaller opening.


Upward tilt of a body in relation to a central axis.


Is a measure of the void in spaces in a material, and is measured as a fraction, between 0-1, or as a percent 0-100%, or empty space compared to 100% solid.

Porous Media

(def from wikipedia) – A solid material (often called a frame or matrix) permeated by an interconnected network of pores (or voids) filled with a fluid (liquid or gas). Usually both the solid matrix and the pore network (also known as the pore space) are assumed to be continuous, so as to form two interpenetrating continue such as in a sponge.


To add weight or force in order to remove compressibility in order to increase the measured stiffness of a bearing or stage. To increase damping. See damping.


Line marking and shaping the outer form of an object. Something viewed from the side, or a description of parameters.


Rotation of a body around a central axis.


(def from wikipedia) – The resistance of an elastic body to deflection or deformation by an applied force. It is an extensive material property. In the International System of Units, stiffness is typically measured in newtons per metre.

Straightness of Motion

A condition relating deviation of a body from perfectly following a straight line.


Leeway for variation from a standard. Allowable deviation from a stated measurement or parameter.

True Position

GD & T specifying desired location. Tolerance must apply w/ two features of a size. Actual placement vs calculated or measured placement in an x,y,z, grid.


Left or right motion of a body around a central axis.

Learn More About the Porous Media Difference