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CMM Reference Spheres / Balls

CMM Reference Sphere

TN United Kingdom (TN UK) is one of the largest manufacturers of contact and non contact CMM reference spheres in the world.

A CMM reference sphere/ball is a part used or purchased with a coordinate measuring machine.

They are known globally as a test sphere, probe calibration sphere, datum sphere or calibration artefact. They are manufactured using Stainless steel 440c, Alumina AL203 Ceramic or Tungsten Carbide.

What Makes a CMM Reference Sphere?

Atypically the CMM References sphere is a precision Ball, attached to a suitable stem, which can be mounted on your CMM Table.

The benefits of TN UK’s CMM Reference Balls

The reference spheres produced by TN UK are manufactured and controlled to extremely tight tolerances. The tight tolerances that we work to ensure that any measurement uncertainties are reduced to the minimum. Giving you the upmost confidence with your measuring equipment.

Using one of our spheres enables the user to take datum points from any angle. All parts can be supplied with certification from our ISO 17025 UKAS approved laboratory to both national and international standards. Enabling direct traceability to the appropriate Standards

CMM Reference Sphere / Balls: Use Cases

CMM reference spheres are used on a coordinate measuring machine (CMM). A styli makes contact with a reference point on the CMM reference sphere, data of the exact dimensions of the sphere being calibrated are added to the measuring software.

If calibrating multiple styli for measuring separate points, the stylus is calibrated with 5 or more reference points on the reference sphere. When using a light scanning calibration system many more numbers of points are used.

CMM Reference Sphere - Technical Drawing
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Ball Diameter
Ball Diameter
Buy Now1550-M6Buy Now
19.050.75-2M6 or 1/4UNF
Buy Now2050-M6Buy Now
Buy Now2550-M6Buy Now
25.41-2M6 or 1/4UNF
Buy Now3075M6Buy Now
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CMM Reference Sphere / Balls Manufacturing Process

All CMM’s provided by TN UK are manufactured, assembled and UKAS certified within our modern facilities in the UK.


Over the last 30 years, TN UK have perfected Precision Ball manufacturing. All our CMM Reference Spheres are precision ground at our facilities to the highest International Standard Grades. Grades available include Grade 3, Grade 5 and Grade 10.


Depending on the application the CMM Sphere can be manufactured using balls made from the following materials:

  • Alumina Oxide AL2O3 Ceramic
  • Tungsten Carbide
  • Stainless steel 440c

Affixing the Stem to the Ball

TN UK affix a pin between the ball and the stem. This is secured with either a threaded pin & adhesive or an adhesive bond. Adhesive bonds can withstand a torque of 500Nm ensuring TN UK manufactured products are robust.

Our Quality Guarantee

Accuracy is our trademark at TN UK. We pride ourselves on our ability to measure and calibrate the products we manufacture. Housing some of the most sophisticated equipment in the world, our annually assessed UKAS lab means we guarantee the precision of the products we supply.

On top of that, we maintain regular and open communication directly with you and any relevant departments to ensure that you get exactly what you need when you need it.

We also offer a recalibrate service for your existing gauges, CMM Reference balls and Master Ball Sets. So you can rest assured that, whether we are supplying a new product or recalibrating an existing one, by meeting our strict standards, your company meets its strict standards (particularly important for other calibration assessed companies).



    Technical Drawings
    PDF (55KB)
    PDF (594KB)


    What is the purpose of Reference Spheres & Balls?

    CMM reference spheres are used to calibrate coordinate measuring machines that are used in the quality assurance stage of the manufacturing process. The reason CMM reference spheres are used is that they ensure the most accurate readings possible. Using a sphere allows an engineer to take measurements from any plane.

    When issuing a UKAS accredited quality certificate the lab will take a reading of the roundness of the sphere by attaching it to a sphericity inspection machine via air suction and having a spindle that rotates around the sphere and measures different planes.

    Often the average of at least 3 planes are used to determine roundness. This is known as the X, Y & Z axis. The more reference points that are used, the tighter the measuring accuracy results become.

    How does Reference Sphere calibration work?

    Reference spheres are produced to incredibly high degrees of accuracy so that they can be used by coordinate measuring machines to check their accuracy. By knowing the exact size of a calibration sphere, the software within a CMM is able to compute whether the movements and readings it is receiving from the machine are accurate. Touch the top centre of the CMM sphere manually with the probe styli and then ok this in the software and the CMM machine will start to calibrate itself from the sphere taking readings by touching the sphere.

    Once a coordinate measuring machine has been calibrated using a reference sphere, it will then be used to check the measurements of a manufactured product. For example, an aerofoil for a turbine engine that must be an exact size in order to function correctly.

    If a CMM reference sphere is not accurate any machine calibrated from it could produce inaccurate results when inspecting the final product.

    How to calibrate a CMM?

    Coordinate measuring machines are calibrated by first placing a calibration sphere on the machines table. The CMM then has a Styli that will move and touch the ball from various angles. Every time there is a touch point, the reading is fed back to the software which calculates the relative position of the styli and if it is where it was expected to be in relation to the spherical surface.

    Due to the high degree of accuracy with which CMM reference spheres are produced, the software is able to tell if the measuring styli is out of position down to points of a micron.