Industry Terms

ABBE ERROR -  the measurement error resulting from angular motion of a movable component and an Abbe offset between the scales measuring the motion of that component and the measurement line.

ABBE OFFSET - the instantaneous value of the perpendicular distance between the displacement measuring system of a machine (scales) and the measurement line where the displacement in that coordinate is being measured.

ACCURACY - quantitative measure of the degree of conformance to recognized national or international standards of measurement.

AUTOCOLLIMATOR - an optical instrument which allows measurement of the angle between its optical axis and a mirror which is imaged through the instrument.

AXIAL ERROR MOTION - error motion collinear with the Z reference axis of an axis of rotation.

AXIS AVERAGE LINE - the average axis of rotation for rotating spindle. The axis average line is obtained by least-squares fitting a line through the centers of several average error motion polar plots at different distances from the spindle face.

AXIS DIRECTION - the direction of any line parallel to the motion direction of a linearly moving component. Due to straightness errors, parallelism, and angular errors, the direction of a linear axis can best be defined by a least square fit of a straight line to the appropriate straightness data.

AXIS OF ROTATION - a line about which rotation occurs.

BACKLASH - a relative movement between interacting mechanical parts resulting from looseness.

BALL BAR - a gage consisting of two high-spherical tooling balls of the same diameter connected by a rigid bar.

BEARING ERROR MOTION - error motion of a rotary axis due to imperfect bearings.

CAP (CAPACITANCE) GAGE - a displacement measuring device of relatively short range and high resolution which functions by measuring the electrical capacitance between the probe tip and the surface being displaced.

CHATTER - vibrations in the cutting process which may damage the cutting tool, the machine, or the part in roughing cuts and degrade the surface finish in finishing cuts. There are basically two types of chatter that can be found on a work-piece; machine chatter and tooling/fixture chatter which leave slightly different surface marking on a part due to the different sources of the vibrations.

COMPLIANCE - the displacement per unit static force between two objects, specified with respect to the structural loop, the location and direction of the applied forces, and the location and direction of the displacement of interest. The following terms can be applied when the structural loop contains an axis of rotation:

RADIAL COMPLIANCE - applicable when the force and displacement directions are at 90 degrees to the reference axis.

AXIAL COMPLIANCE - applicable when the force and the displacement are collinear with the Z reference axis.

TILT COMPLIANCE - applicable for a pure moment and a tilt displacement in a plane containing the Z reference axis.

FACE COMPLIANCE - applicable when the force and displacement are parallel to the Z reference axis and at a specified radial location.

LINEAR COMPLIANCE - applicable when the force and displacement are applied to a machine axis designed for linear motion. Linear compliance can be in the direction of the slide axis or perpendicular to that direction.

ANGULAR COMPLIANCE - applicable when a pure moment is applied to a rotary axis in the direction of the designed angular displacement.

COSINE ERROR - the measurement error in the motion direction caused by angular misalignment between a linear displacement measuring system and the gage or displacement being measured.

CRITICAL SPEED - a spindle speed which is such that at that speed and tool combination a minimum in the lobing diagram would be encountered

DEAD PATH - in laser interferometry, that distance between the remote interferometer and the retro-reflector at closest approach which is not compensated for changes in the index of refraction of air.

DIAGONAL DISPLACEMENT - the displacement of the “tool” of a machine tool along either a face or body diagonal of its work zone.

DRIFT TEST (THERMAL) - a type of test used to measure temperature variation error on a machine. One form of this test consists of continuously recording the output of displacement sensors placed in the position of a part on the machine and reading against a test ball mounted in the machine spindle over a period of time.

ERROR - the difference between the actual response of a machine to a command issued according to the accepted protocol of that machine’s operation and the response to that command anticipated by that protocol.

ERROR MOTION - change in position relative to the reference coordinate axes, or the surface of a perfect work-piece with its center line coincident with the axis of rotation. Error motions are specified as to location and direction and do not include motions due to thermal drift.

ERROR MOTION MEASUREMENTS - a measurement record of error motion which should included all pertinent information regarding the machine, instrumentation and test conditions.

ERROR MOTION POLAR PLOT - a polar plot error motion made in synchronization with the rotation of the spindle. The following terms applies to the error motion polar plot and its components:

FACE MOTION - error motion parallel to the Z reference axis at a specified radial location.

GAGE - a mechanical artifact of high precision used either for checking a part or for checking the accuracy of a machine, or a measuring device with a proportional range and some form of indicator, either analog or digital.

GAGE LINE - a reference plane in or near the spindle nose and perpendicular to the spindle center line.

HYSTERESIS - a component of bi-directional repeatability caused by mechanisms such as drive train clearance, guide-way clearance, mechanical deformations, friction, and loose joints. Two types of hysteresis are defined:

SET UP HYSTERSIS - the hysteresis of the various elements in a test setup. Normally due to loose mechanical connections

MACHINE HYSTERESIS - the hysteresis of the machine structure when subjected to specific loads.

INERTIAL VIBRATION - for the purposes of machine tool testing, inertial vibration is defined as vibration of the support surface on which the machine tool is mounted which is induced as the result of external forces in the surrounding area.

LASER INTERFEROMETER - a fringe counting interferometer for displacement measurement which uses a laser as a light source.

LATHE - any one of a class of machine tools where the part to be machined is rotated in a spindle in order to provide the surface speed necessary for metal cutting.

LINEAR DISPLACEMENT ACCURACY - the difference between the true displacement of a tool along a machine axis and the recorded by the machine measuring system. For the purposes of machine tool testing, this difference is understood to be the maximum systematic error from any point to any other point within the machine travel.

LINEAR VARIABLE DIFFERENTIAL TRANSFORMER (LVDT) - an electromagnetic device used for displacement measurement. Normally an LVDT has the capability to convert a displacement into a proportional electrical signal.

LOAD CELL - a transducer which is used to measure force. Normally a load cell has the capability to convert a force into a proportional electrical signal.

MACHINE COORDINATE SYSTEM - the coordinate system which corresponds to the axes of the machine on which a part is to be manufactured. The coordinate system usually includes one or more linear axes designated X, Y, or Z. The machine may also include rotary axes usually designated A, B, and C.

MACHINING CENTER - a computer numerically-controlled machine tool with a spindle equipped for holding rotating tools. Such a machine shall also have tool changing capabilities and be capable of automatically performing multiple operations, including milling, drilling, tapping, and boring.

MEAN AMBIENT TEMPERATURE - the mean temperature of the ambient environment surrounding a machine as computed from at least two readings taken at the center of the machine’s work zone during the interval required for the test.

MEAN SCALE TEMPERATURE -the mean temperature of a machine scale as computed from at least two temperature readings taken on that scale during the interval spanning the time required for a test.

MEAN TEMPERATURE - the average temperature computed from a stated number of temperature measurement at equally spaced time intervals at a specific location.

MEAN GAGE TEMPERATURE - the mean temperature of a gage used for machine testing as computed from at least two readings taken on the gage during the interval required for a test.

MEASUREMENT LINE - a line in the work zone of a machine along which measurements are taken.

MEASUREMENT POINT - a point in the work zone of a machine at which machine coordinates are recorded as part of a measurement.

MOVABLE COMPONENT - a major structural component which is movable relative to the machine base during measurement.

NOMINAL COEFFICIENT OF THERMAL EXPANSION - an estimate of the coefficient of thermal expansion of a body. For the purposes of machine tool testing and in reference to the nominal coefficient of expansion of machine scales, it shall mean the effective coefficient of the scale and its mounting to the machine as measured in line with the scale for typical machines of the given design. Since the true coefficient for a given machine is not known, an uncertainty must be applied when making nominal differential expansion corrections.

NOMINAL DIFFERENTIAL EXPANSION - the difference in thermal expansion between a machine’s scales and a test part as computed using the nominal expansion coefficients for the scales and part.

NON_SENSITIVE DIRECTION - any direction perpendicular to a sensitive direction.

OPTICAL PLOYGON - an optical element composed of a number of plane surface mirrors arranged to form a regular polygon.

PARAMETRIC - for the purposes of machine tool testing, parametric is defined as referring to the measurement of any of the geometrical error terms of a machine. These include, for example, angular errors, straightness errors, spindle errors, and alignment errors such as parallelism and squareness.

PART COORDINATE - the Cartesian (X, Y, Z) coordinate system in which the part is defined and in which the tool coordinates are specified.

PERFORMANCE TEST - any of a number of test procedures which are used to measure machine performance.

PERIODIC ERROR - an error in the linear displacement accuracy of a machine that is periodic over an interval which normally coincides with the natural periodicity of the machine scales. For example, in a lead screw driven machine with rotary encoders, the periodicity is usually synchronous with the pitch of the lead or ball screw.

PITCH - the angular motion of a carriage, designed for linear motion, about an axis perpendicular to the motion direction and perpendicular to the yaw axis.

PLAY - a condition of low zero stiffness over a limited range of displacement due to clearance between members of the structural loop.

PROBE - for purposes of machine tool testing, a device which establishes the location of the movable components of a machine tool relative to a measurement point. Three types of probes are discussed:

SWITCHING PROBE - a probe that gives a binary signal as a result of contact with or in proximity to a work-piece.

PROPORTIONAL PROBE - a probe that gives a signal proportional to a displacement of the probe from its free position. Most commonly such probes use linear, variable differential transformers as displacement sensors and have electronic readout. Such probes are preferred; however, in lower accuracy applications, a dial gage can be used.

NULLING PROBE - a probe which, in reference to a work-piece, gives a signal which causes the machine to be driven to a position that will null the probe reading.

PROBE APPROACH DISTANCE - the distance of approach to the apart at which the machine traverse speed is reduced to the probe approach rate for measurement.

PROBE APPROACH RATE - the nominal speed of approach of the probe toward the part during the acquisition of data.

PROBE CYCLE - a fixed cycle using a probe.

PROBE LOBING - a systematic error in the measuring accuracy of probing systems such that a measured value depends on the displacement direction of the probe tip.

PROCESS DAMPING - a condition in milling where the wavelengths of undulations created by chatter the cut surface decreases, the slope of these waves increases, and the damping component of the cutting force strongly increases, thus attenuating the regeneration of waviness.

PURE RADIAL MOTION - the concept of radial motion in the absence of tilt motion.

RADIAL ERROR MOTION - error motion of rotary axis normal to the Z reference axis and at a specified angular location.

RANGE - the difference between the maximum and minimum values of a set of measurements of nominally the same quantity.

REFERENCE COORDINATE AXES - mutually perpendicular X, Y, and Z axes fixed with respect to an object.

RELATIVE VIBRATIONS - for the purposes of machine tool metrology, relative vibration refers to non-zero frequency relative motion between the position of a nominal tool and nominal work-piece.

REPEATABILITY - for the purposes of the Glossary, repeatability is defined as a measure of the ability of a machine to sequentially position tool with respect to a work-piece under similar conditions. Repeatability is defined on a per-axis basis.

RESOLUTION - the least increment of measuring device. On a digital instrument, the least significant bit.

RETROREFLECTOR - an optical element with the property that an input light beam is reflected to return along the same angle as it was incident.

ROLL - the angular motion of a carriage designed for linear motion about the linear motion axis.

ROTARY AXIS - any notion axis of a machine whose function is to provide a rotary motion either for the purposes of positioning of for moving a part or a tool to provide sufficient surface speed for cutting (i.e. a spindle). In this Definition of Terms, three types of rotary axes are defined. They are:

ROTARY MACHINING AXIS - a rotary axis where the axis can be used to provide continuous-path contour cutting in a rotary direction.

ROTARY POSITION AXIS - a rotary axis which allows the rotation of a part into a new position for the purposes of cutting only; that is, this axis is not used to provide continuous contour cutting, but only to reposition different faces of the part for the purpose of metal removal.

RUNOUT - the total displacement measured by an instrument sensing against a moving surface or moved with respect to a fixed surface.

SAFE OPERATING TEMPERATURE RANGE - the temperature range in which a machine tool may be expected to operate without physical damage to the machine or its support systems (i.e. computers, controllers, etc.).

SCALE - a readout device which has the purpose of providing the linear or rotary position of a machine axis. For the purposes of machine tool metrology, the readout device could be a line scale, inductive scale, a ball screw, a lead screw, a shaft encoder, or any type of linear or rotary readout devices. Where temperature is mentioned in this Glossary with respect to a scale, it refers to the temperature of the material which composes the portion of the scale which establishes the unit of length. That is, in a line scale, it refers to the matrix on which the lines have been deposited; for a leader ball screw, it refers to the temperature of the material composition of the screw itself, etc.

SENSITIVE DIRECTION - the direction where relative motion between the tool and the work-piece causes one-for-one form errors to be cut into the work pieces. On machining centers with a rotating tool, the error motion of the spindle must be considered to be of the rotating sensitive direction type. As in boring, the cutting tool rotates with the spindle. Two types of sensitive directions are recognized:

FIXED SENSITIVE DIRECTION - the work-piece is rotated by the spindle and the point of machining or gauging is fixed.

ROTATING SENSITIVE DIRECTION - the work-piece is fixed and the point of machining or gauging rotates with the spindle.

SETTLING TIME - the time required between contact of a proportional probe with a measurement point and the time at which valid data may be taken.

SOCKET - a socket that allows the accurate repositioning of one end of a telescoping ball bar.

SPINDLE - a device which provides an axis of rotation, for the purposes of rapidly rotating a part or a tool to provide sufficient surface speed for cutting operations.

SPINDLE SPEED - the rate of rotation of a machine spindle usually expressed in revolution per minute.

SQUARENESS - a plane surface is “square” to an axis of rotation if coincident polar profile centers are obtained for an axial and face motion polar plot at different radii. Also, for linear axes the angular deviation from 90° measured between the best fit lines drawn through two sets of straightness data derived from two orthogonal axes in a specified work zone.

STAGING - the moving of a gage from first position to a second position such that a series of measurements started in the first position may be continued in the second position.

STATIC ERROR MOTION MEASUREMENT - a special case of error motion in which the error motion is sampled with the spindle t rest at a series of discrete rotational positions.

STEERING MIRROR - a mirror used to steer the laser beam to the appropriate angle in the diagonal displacement measurements in a direction of linear motion.

STEP GAGE - a gage comprising a rigid bar with calibrated steps used for determining accuracy of distance measurements in a direction of linear motion.

STIFFNESS - the reciprocal of compliance.

STRAIGHTNESS ERROR - slide straightness error is the deviation from straight line movement that an indicator positioned perpendicular to a slide direction exhibits when it is either stationary and reading against a perfect straightedge supported on the moving slide, or moved by the slide along a perfect straightedge which is stationary.

SYSTEMATIC ERROR - that portion of a machine error that results from computing the mean of a very large number of similar measurements.

TEMPERATURE VARIATION ERROR (TVE) - an estimate of the maximum possible measurement error induced solely by deviation of the environment from average thermal conditions

THERMAL ERROR INDEX (TEI) - the summation, without regard to sign, of the estimates of all thermally induced measurement errors expressed as a percentage of the working tolerance.

TILT ERROR MOTIONS - error motion in the angular direction relative to the Z reference axis tool change under program control: the process on a machining center or work center where the cutting tool is exchanged, usually with its tool holder, for another tool under control of the part program; ie. without human intervention.

TOOL (FIXTURE) OFFSET - a relative displacement that is applied to an axis of a machine for a specified portion of the whole of program and cause a displacement in that axis only in the direction determined by the sign of the offset value.

TOOL LENGTH OFFSET - An incremental displacement in the axial direction of the tool.

VIBRATION AMPLITUDE - peak-to-peak amplitude of a given frequency component of a vibration spectrum.

WOBBLE PLATE - a mechanical device which allows the tilting (wobbling) of a test fixture by adjustment screws.

WORK ZONE - working (machining) volume of a machine as specified by the supplier. More than one work zone may be specified for a given machine, and working tolerances may be specified separately for each work zone.

YAW - the angular motion of a carriage, designed for linear motion, about a specified axis perpendicular to the motion direction. In the case of a carriage with horizontal motion, the specified axis shall be vertical unless explicitly specified. For a carriage that does not have horizontal motion, the axis must be explicitly specified.

REBUILD to return your machine to like new condition in order to perform to the manufacturer’s specification and extend the working life of the equipment.

CONTROL RETROFIT to enhance the productivity of your machine by upgrading with the latest control technology and features, from PLC integration to full CNC control retrofit; increase performance and throughput. A complete control retrofit includes replacing the machine wiring, sealtite and electrical enclosure and occasionally machine electrical devises and components. Control, motors and drives “only” control retrofit - to enhance the productivity of your machine by upgrading with the latest control technology and features, from PLC integration to full CNC control retrofit; this retrofit service also increases performance and throughput but at a reduces cost. A Control motors and drives “only” control retrofit retains the machine wiring, sealtite, electrical enclosure and all of the existing electrical devises and components. However, we do replace the existing servo motor armature and feedback cables with new

REMANUFACTURE - “State of the art” modifications to a machine’s design and performance in order to meet new productivity demands; enable machine to perform better than when it was new.