Select Calibration Incorporated

Calibration Services for Coordinate Measuring Machines


This page contains links to articles related to coordinate measuring machines and inspection.  All articles are provided in PDF format and can be opened using any PDF viewer.

Calibration Sphere Form Error

Calibration Sphere Form ErrorThis article describes the effect of form error on a sphere when used as a calibration artifact on a CMM. The purpose of the calibration sphere is to determine the effective stylus tip diameter and relative probe offset between multiple probe positions. Multiple probe positions can be from a fixed head with more than one stylus or a single stylus on an articulating probe head.

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Comparison Between ISO/IEC 10360-2:2009 and ASME B89.4.1:1997 Performance Standards

ISO 10360 vs ASME B89.4.1This document describes the testing method and results from a comparison of the two major performance testing standards for coordinate measuring machines; ISO/IEC 10360-2:2009 and ASME B89.4.1:1997. The ASME B89.4.10360-2:2008 is identical to ISO/IEC 10360-2:2009 therefore the results apply to both standards.

The Renishaw Machine Checking Gauge is included in the comparison tests as a point of reference. This gauge is ideal for CMM interim checking due to its speed and ease of use so therefore a comparative test using this gauge to established standards seemed appropriate.


CMM Measurement Uncertainty Budget

CMM Measurement UncertaintyThis article describes a generic uncertainty budget when using a CMM for inspection. The estimation of measurement uncertainty is a requirement for ISO/IEC 17025.

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Temperature Compensation

Temperature CompensationThis article describes the reasons for having the environment of a coordinate measuring machine at the standard reference temperature of 20 ̊C and the effects of using a CMM at a non-standard temperature. This article also looks at common methods used to compensate for temperature and the types of materials used in the construction of CMM's that have an impact on how the machine will perform when temperature changes.

Temperature variation in a lab environment, when using a coordinate measuring machine, can be a large source of measurement error. Partial solutions to temperature related problems exist but do not address all problems and may even introduce collateral problems in the process.


Compensation Map Increments

Map IncrementsThis article is written as a guide for the choice of compensation map increments used on coordinate measuring machines. Selecting a suitable increment is important since a step size that is too large or too small will result in a loss of machine accuracy. Often the actual compensation map increment is selected based on secondary reasons (i.e. matches the increment of a step gauge or is simply a round number). In some cases map increments are selected with the belief that using a very small increment will improve the performance of the CMM. Most calibrators only have one opportunity to fully map a machine so comparative tests where the map increment is adjusted are never performed.


Compliance Statements

Compliance StatementsOften the biggest question when performing any kind of measurement is simply “is it in spec?”. In some cases it is very clear that the measurement is either inside or outside of specification and in other cases, particularly when the measurand is close to the specification, it is not so clear and cannot be stated with any kind of confidence either way. Often measurements close to the specification, when simply repeated, can appear to shift from one side of the tolerance to the other. This kind of situation can be accurately described as simply unknown.

This article is about compliance statements and the accepted practices for expressing compliance to a specification. When expressing an opinion of compliance from the performance tests on a coordinate measuring machines following any recognized standard, such as ASME B89.4.10360 or ISO/IEC 10360, it is necessary to do this with a suitable level of confidence particularly if traceability is a requirement.


Horizontal Arm Deflection

Horizontal Arm DeflectionHorizontal Arm coordinate measuring machines have a unique problem due to their cantilever design. As the arm extends the center of gravity changes resulting in a measurable deflection in the tower of these machines.

This article describes some of the problems related to calibration of horizontal arm coordinate measuring machines and effects of deflection. All manufacturers of horizontal arm CMM's have provisions for dealing with tower deflection as this is a common problem for this type of machine.


CMM Interim Testing

Interim TestingInterim tests are performance checks of a CMM that are done regularly between calibrations. Interim checks are important as they can proactively indicate that a problem exists with a machine and can also provide confidence in the equipment.

This article is written to describe different methods for CMM interim checks.


CMM Kinematic Axis Order

Kinematic OrderTo describe the significance of the kinematic axis order of a CMM machine. The kinematic order defines how the machine axis are interconnected and is used as part of the machine compensation data to correct for known errors. An incorrect kinematic order means the software is not capable of compensating for the known machine errors properly and may actually increase the measurement error of a CMM.


Applying Compensation Map Data

Applying Compensation Map DataThis article is written as a practical example of how to interpret compensation data from a coordinate measuring machine and create a correction value and tool coordinate system for any position in the measuring volume. This information can be used to build a working model for error map correction and can be useful for developing other utilities to allow interpretation or correction based on measurement data.


Errormap Rotation Point

Errormap Rotation PointThis article describes the significance of the position selected as the rotation point for a coordinate measuring machine compensation errormap. Recently an example was found that highlighted problems as a result of selecting a mathematical rotation point at a location different than the mechanical rotation point. The effect was clear on the linear data from the compensation map.

The ideal position for the rotation point is always the same as the mechanical rotation point the the axis of a CMM. One example where placing the rotation point inside the volume of the CMM is desired is when the goal is to have all the parameters collected then built into a compensation map in one step. This is more a case where the advantage of having the ability to collect all the data then building the map in one step outweighs the disadvantages of not having the rotation point at the mechanical origin.