Long Bore CMM

Our groundbreaking Long Bore CMM provides a solution to one of the last great challenges in Metrology; that of offering precision measurement down long or deep bores.

Specifically developed for the measurement of tubular items for example; jet engine shafts, undercarriage components, power generation plants, oil industry and defence requirements.

The Long Bore Measurement (LBM) is patented in areas critical to its precision.

Eley Metrology Ltd has for forty years offered world-class products and continues to be at the forefront of metrology developments.

As worldwide demand continues for better quality solutions, the LBM demonstrates Eley’s expertise in this field.

Long Bore CMM

Overview of the LBM Functionality


The LBM is unique and offers a solution to an area of Metrology that has always presented a challenge i.e. the precision measurement of features down long deep bores. The machine is totally designed and manufactured by Eley Metrology.

Applications include: aerospace components like main engine shafts, hydraulically operated under-carriage landing gear, nuclear reactor items, oil industry components, line bored bearing housings and indeed any component where the precision measurement of features inside long deep bores are of interest. Perhaps one of the best examples is highlighted by the critical requirements of a jet engine main shaft.

Such a component will be required to rotate in use possibly at 20,000 rpm. The centrifugal forces involved are immense. It is vital that the geometry and size of such a component is in compliance with the engine designers exacting specifications and requirements.

Concentricity of inner and outer shaft bearing diameters are critical along with the blend radii of various internal and external diameters. All features must be measured in relationship to the centreline of the shaft. Any out of tolerance will cause serious vibration problems with possible catastrophic consequences if not identified before build of the final engine assembly.

The LBM offers unique performance when measuring:

• Concentricity between inner and outer diameters.
• Circularity and Cylindricity measurements.
• Pitch Circle diameters. – PCD’s
• Fillet radii between diameters.
• Straightness and parallelism for component centre line datum.
• Partial Arc measurement

With previous old measurement procedures, composite measurement reports were produced employing dial indicators and gauging techniques. Often the budget for uncertainties of measurement alone could often take the component specification outside the available tolerance band. This is why the LBM was conceived. With greater demands for precision by designers along with more superior manufacturing machines, so the need for more accurate and certain measurement had arrived. This we might say is how progress is made!


Specification (Written in millimetres and is directly converted to the Inch equivalent by the system)

• Resolves to .5 of a micron. (.0005) m/m / .000019685”
• Certified in accordance with ISO 10360/2 : 2002
• Volumetric measurement capacity of better than forty microns at the end of a measuring lance of 3.0 metres / 118.11”
• Non-error mapped due to manufacturing excellence
• The specification over the entire length of the X axis guide is seven microns in total, including parallelism and straightness
• The Y and Z axis are within two microns of straightness and parallelism.
• Analysis software: Eley’s True Measure 4 (TM4)
• Direct Inch/Metric Conversion

Note; 1 Micron = .00003937”


The LBM Long Bore CMM Features

The LBM smallest diameter lance can pass through a bore as small as 20 millimetres diameter in order to measure a feature.

The LBM is equipped with two Z spindles called Primary and Secondary.  They are constructed in a parallelogram providing essential stability to the Z axis of the LBM.

The guidance system is that of a Vee-flat configuration and employs patented air-bearings that are pre-loaded throughout.

The LBM can measure from beneath the Primary Z spindle and so can offer convention CMM measurement.  The same datum can be used to that of the touch probe at the end of the main lance.

The LBM does not employ any error mapping or computer correction.  UKAS Certification and Volumetric Specification is therefore achieved without this.

Precision Straightness and Squareness of machine geometrics are derived from the excellence demanded at the manufacturing stage of the main guides.  The X axis guide has a specification of seven microns total and the Y and X axes is produced within two microns total.



To supplement the ISO 10360 standard, Eley Metrology carry out further verification employing a system of traceable Master Ring Gauges set in a fixture. Each ring carries certification of the main Internal Diameter and Concentric External Diameter.

The object of the Master Rings is to replicate the measurement problems created by a precision tube. Therefore, demonstrating the ability to display Diameters, Internal and External and their concentricity’s. In addition to quantifiable examples with respect to wall sections of components.


LBM Long Bore CMM Applications

Applications include aerospace components such as main engine shafts, hydraulically operated under-carriage landing gear, nuclear reactor items, oil industry components, defence systems components and line-bored bearing housings.


A Custom Range of Machine Sizes are Available on Enquiry

The Precision Long Bore CMM is manufactured to customer requirements. As standard, our comprehensive after sales and support team are always on hand to ensure your LBM is operating correctly.


Find Out More

If you’d like more details about the Long Bore Measurement (LBM), then our team are available to help.

Call Us: +44 (0) 1332 367475

Email: sales@eleymet.com

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