The importance of precision, accuracy, and efficiency cannot be overstated for Coordinate Measuring Machines (CMMs). On top of the features and characteristics inherent to each CMM, the accompanying accessories augment its functionality and boost its performance. From hold-down clamps to calibration artifacts, each accessory plays a crucial role in improving measurement accuracy, precision, and convenience. In this comprehensive guide, we’ll navigate through the top 19 CMM accessories that are essential for every CMM professional. Regardless of whether you’re an experienced technician or a novice in the field of metrology, these accessories provide invaluable solutions to the common challenges encountered in CMM operations.
- Hold-Down Clamps
Hold-down clamps thread directly into base plates, fixture plates, and similarly compatible fixture components. The clamps slide along the shaft and are oriented onto the workpiece. Pressing down on the clamp creates a light hold on the workpiece keeping it securely in place. The advantages of hold-down clamps are their accessibility (use directly with fixture plates), simplicity, and dependability. Some disadvantages are only providing a vertical clamping force, limited use with abnormally shaped workpieces, and limited fixture repeatability.
- Fixture Plates
Fixture plates, typically made of aluminum or acrylic for optical systems, have a grid pattern of 1/4″-20 threaded holes spaced at 1/2″ apart. They are made in various sizes and are used in a variety of measurement systems for attaching fixture components. The rows and columns are marked alphanumerically for identifying holes, which is very helpful for measurement repeatability.
- Fixture Towers
Mounting directly to fixture plates, fixture towers are structures of aluminum made for spanning fixture support on large workpieces. The towers are made of various lengths and have grids of 1/4″-20 threaded holes for attaching fixture components. They are also marked alphanumerically for easy identification of the holes.
- Angle Plates
Angle plates can fixture a workpiece from a different work-plane such as a right angle. These components are especially convenient when a workpiece needs to be held from the side and be accessible from below.
- Standoffs
Standoffs are key components of a CMM toolkit. They can serve multiple purposes in setting up CMM fixtures such has providing elevation, modularity, and customization. Specialized standoffs may have magnets for holding steel or iron parts and v-shaped for holding cylindrical parts.
- Styli
Probe styli are responsible for a significant contribution the of measurement precision of a CMM. It is vitally important to maintain an inventory of spares for the most commonly used probe sets. Probes can be made of various materials such as ruby or silicon nitride and in may sizes and configurations.
- Stylus Extensions
Stylus extensions are key to building a probe setup that measures hard-to-reach areas. Extensions can vary widely in length, diameter, material, and thread size. Weight and rigidity of extensions should always be considered when building a probe set in order to properly account for potential sources of measurement error.
- Break Stems
Probe crashes on a CMM are inevitable eventualities. Break stems are are threaded components that are assembled between a probe and its stylus and are designed to fail first in the event of a collision, protecting the expensive and sensitive parts of the CMM.
- Stylus Thread Adapters
Stylus thread adapters are incredibly useful is some cases when building up a probe set of various stylus sizes. They allow you to thread smaller tips onto much large probe set bodies.
- Calibration Artifacts
In order to provide official measurement traceability of a CMM or to reinforce the confidence of the measurement results, calibration artifacts are an essential part of a CMM toolkit. Calibration artifacts are used by OEMs and external service technicians to validate and verify a CMM calibration. However, calibration artifacts can also be used internally to provide validation of measurement results. They are incredibly useful to run after a crash to help determine if the CMM received damage that affects the measurement results.
- Probe Storage Racks
Probe storage racks solve the problem of having several probe setups that are frequently used on the CMM. They are typically made of aluminum or lightweight material and positioned near the rear or side of the CMM’s measurement volume. During CNC operation, some CMMs can automatically place and remove probe setups as needed.
- CMM Cleaning Kit
Keeping a CMM and its environment clean is essential to maintaining the OEM reported measurement uncertainty of the instrument. Basic cleaning solutions such as alcohol can be used to clean most surfaces on a CMM. Be cautious of cleaning linear scales, probes, etc. since some solutions may cause issues or damage with sensitive components. Always follow recommended OEM maintenance procedures.
- Styli Wrench
A styli wrench is a very simple tool that can alleviate a lot of issues with building up and tearing down probe sets. Most CMM probes are built with very small components which are usually difficult to hold and tighten (tight probe sets are essential to maintaining accurate and precise measurements).
- V-Block
V-blocks are an important and fundamental fixture on a CMM. They excel at securing cylindrical parts and often have built-in magnets (some of which can be toggled on and off).
- Pocket Ruler
CMMs can produce measurement results with uncertainties on the order of magnitude of 1 micron but sometimes its necessary to have a pocket ruler or scale to visualize CNC movements and clearances of a few millimeters or more.
- L-Square
L-squares are tools that will help solve CMM alignment issues and probe shanking before they occur. Use an L-square to align an edge on the part perpendicular to the CMM. This will stabilize the alignment measurements on the CMM and prevent many opportunities for bad probe hits.
- Magnifying Glass
Often times, it is necessary to have a magnifying glass handy when operating a CMM. Sometimes the feature of measurement is too small to clear see with the naked eye. Also, a magnifying glass is needed to look for stylus tip damage and/or wear.
CMM Accessory Vendors
Renishaw
Carbide Probes
McMaster-Carr
References and Further Reading