Understanding Truing & Dressing

David S. Goetz, Senior Corporate Application Engineer, Norton | Saint-Gobain

Properly maintaining a grinding wheel’s performance and accuracy relies on truing and dressing. These processes also help optimize your grinding efficiency and improve your productivity over the life of your wheel. But just what are truing and dressing?

Not the Same Thing

Because they are most often performed at the same time, truing and dressing are often thought of as a single process. That, however, is not accurate. In reality, these are two independent processes.

Truing is all about a grinding wheel’s shape or profile and its alignment with the grinder.

This involves:

• Adjusting the wheel’s diameter to make it run true with the axis of rotation
• Restoring the wheel profile to its proper geometric shape in response to wheel breakdown from use
• Changing the profile of the wheel to the desired shape

Dressing is all about a wheel’s grinding face condition and refreshing it to expose fresh grains and restore the wheel’s sharpness or to create a condition that will generate a better workpiece finish. 

This involves either:

• Opening the wheel face by the removal of dull abrasive particles to allow for the exposure of sharp cutting points and/or the removal of foreign material from a “loaded” wheel (a loaded wheel is one that is “clogged” with material removed from a work surface)
• Closing the wheel face by dulling the abrasive particles to generate a finer surface finish

Choosing the Right Dressing Technique

Dressing only alters or affects the wheel face condition, leaving the wheel face in either of two conditions – either open or closed. An operator will choose which condition is preferred depending on the process requirements.

Here are the differences between open and closed dressing:

Methods for Truing and Dressing

Just as abrasives are harder than the materials they are used on, dressing tools need to be harder than grinding wheels. Diamonds are commonly used in truing/dressing products because they are the hardest known substance on earth and have high thermal conductivity. Both natural and synthetic diamonds are used in dressing products. 

Here are some of the most common types of tools used:

Each tool has its advantages depending on the requirements of the application. For more information on selecting a dressing tool, read our "Optimize Grinding Processes with Proper Truing and Dressing Tools" article.

Although every grinding operation or application is unique, the indicators used to tell when truing and dressing are needed are very common. 

These indicators include:

• Grinding Power – As the wheel face begins to close or dull, the power required will climb. If this gets too high, there is a risk of metallurgical damage. Dressing the wheel at a specific power threshold prevents that.
• Form Loss – As the wheel is used, the profile or flatness can and will change as the wheel breaks down. Regularly checking the parts for geometry and truing the wheel regularly prevents parts being made that are out of tolerance.
• Finish – Much like form loss, dressing the wheel regularly to maintain the face condition will allow you to maintain a specific finish and keep parts from being made with too fine or too rough of a finish. 

The frequency required for truing and dressing is also unique to each application and grinding wheel specification. Thus, this can only be determined over time. To know how often a given wheel will need to be trued or dressed requires an understanding of the application and usually involves several runs of parts to track part geometry and/or finish. This helps establish when/where the wheel begins to suffer so an appropriate truing and dressing frequency can be defined.