Glossary of Terms
Clearance fit
A condition where one mechanical part is fit into another in such a way as to leave a small gap or clearance between parts.
CNC
Abbreviation for computer numerically controlled. CNC refers to machining equipment where tool motion and spindle speeds are controlled by a computer.
Fatigue
Weakness in metal, wood or other material resulting from prolonged stress.
F.P.M.
Feet per minute. A measurement of velocity in terms of the distance traveled in feet over a period of one minute.
Friction
A force tangential to the common boundary of two bodies in contrast that resists the motion or tendency to motion of one relative to the other.
Hardness
The relative resistance of a metal to denting, scratching, or bending. Hardness of metallic shafts is typically expressed as a relative value from the Rockwell C or Brinell hardness scales.
Housing
A frame, bracket, or box for holding or protecting a mechanical part. Ex. bushing plate.
I.D.
Inside diameter. A measurement taken from a point on the inner surface of a round object, along a straight line through the center of the object to a point on it’s opposite inner surface.
Interference fit
The condition whereby one part slightly oversized is fitted into another.
Keyway
A slot in a shaft or liner to accept a key for a positive drive.
Line on line fit
Also called a line fit. An assembly where one part fits into another with a close sliding fit, without significant clearance or interference.
Liner
A liner is also referred to as a bushing, it is the rotary inner member of a rotary bushing.
Lip
Refers to the rim edge of a seal, especially at the point where sealing contact is formed against the mating surface.
Load
The overall force to which a structure is subjected in supporting a weight or mass, or in resisting externally applied forces.
Lubrication
A film of oil or grease used to reduce friction between two mating parts.
Metric
Designating, pertaining to, or using the metric system, a decimal system of weights and measures based on the meter as a unit length and the kilogram as a unit mass.
Nominal
Of, being, or related to a designated or theoretical size that may vary from the actual.
O.D.
Outside diameter. A measurement taken from a point on the outer surface of a round object, along a straight line through the center of the object to a point on it’s opposite outer surface.
O-ring
A ring, typically made from synthetic rubber, used as a seal.
Press fit
An assembly of mechanical components whereby one piece , due to dimensional interference with another piece, fits so tightly that it must be pressed into place with some force.
Retainer
Any device that holds a mechanical part (such as a bearing) in a particular place or position.
Rotary
Of, pertaining to, causing, or characterized by rotation.
Rotary Bushing
A self contained bearing cartridge used to support and guide rotating cutting tools.
Rotary Toolholder
A combination of a solid toolholder with an exterior bearing assembly which pilots in a stationary drill bushing, used to accept cutting tools for machining operations.
Rotation
Motion in which the path of every point in the moving object is a circle or circular arc centered on a specific axis, especially on an internal axis.
R.P.M.
Revolutions per minute. Unit of measure for rotary motion, designating the number of complete revolutions of an object over a period of one minute.
Runout
The deviation from true center of points on the surface of a rotating shaft.
Seal
Any device used to prevent the passage of fluid or contamination.
Shaft
A slender, straight round bar. A shaft is the rotary portion on a rotary toolholder.
Surface finish
The texture produced by the last treatment or coating on the surface of an object, especially on the mating surface contacted by the seal.
T.I.R.
Total indicator reading, Refers to the maximum deviation from a true center line of a surface of a round shaft during rotation, as measured with a dial indicator.
Tolerance
The permissible deviation from a specified value of a structural dimension.