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Assessing the Accuracy of Thickness-Measurement Tools

(April 2004) posted on Tue Apr 13, 2004

Discover what tools and procedures lead to the most accurate measurements for screen printing.


By Fernando Zicarelli

This article will show that thickness variations generally are caused by variables within the thickness gauges themselves. It also will compare the most common types of thickness gauges and assess their overall accuracy.

Understanding thickness gauges

Most of the thickness gauges used in the screen-printing industry are contact gauges--meaning they make physical contact with the item being measured--and all provide some form of digital readout. When using a contact gauge for screen or stencil measuring, it's essential to have a flat, solid surface or base on which the mesh will rest during the measurement process. The base provides a firm contact point when the measuring probe is lowered onto the mesh.

Gauging force is the force that the contact probe applies to the mesh or stencil. Excessive force can deform the measuring probe's tip and the material being measured. And if the force is too small, any lint or foreign particle on the mesh could prevent the probe from making full contact. The actual amount of gauging force to use with a thickness gauge depends on how the device deploys its contact probe during the measuring process. I have documented gauging forces ranging from 0.01-8 Newtons (N).

The deployment mechanisms found on thickness gauges fall into three categories: spring actuated, pneumatically driven, or electrically motorized. With a spring-actuated gauge, the operator depresses a lever to retract the contact probe, then places the mesh on the measuring base. With the mesh in place, the lever is released and the probe deploys to take the thickness measurement. Such gauges rely on a spring that compresses when it is retracted or extends when it is released.

 

The measuring force applied by spring-driven gauges can vary depending on how much the spring is extended or retracted. In theory, if too much force is applied to compress the spring, this might cause the spring to push back too hard against the item being measured and compress it, thereby leading to an inaccurate reading. However, gauge manufacturers say that as long as the spring's stroke length isn't exceeded during compression, the readings will remain accurate.

Pneumatic thickness gauges use air pressure to extend the probe for measuring. The level of air pressure, and consequently the measuring force applied, can generally be controlled by the user.


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