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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.

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By Fernando Zicarelli

In the final category, you'll find gauges that rely on motorized actuation. On these systems, the contact probe is raised or lowered at the push of a button. Motorized units generally provide a range of measuring forces from which the user can select. This is the type of probe I used for a portion of my thickness-measurement study.

The contact probes employed in measuring gauges also come in various configurations and sizes. The most common probe shapes are round, domed, and flat (Figure 1). Flat-surface probes are the most common type and are generally offered with diameters of 1.5, 4.8, 6, 7.2, or 10 mm.Assessing the Accuracy of Thickness-Measurement Tools

Figure 1 Probe Types Thickness gauges support a variety of probe shapes and sizes, including flat, domed, pin (a small diameter flat probe), and round. Flat probes return the most accurate results when measuring mesh and stencil thickness.

Probe shape, size, and measuring force

In the first part of my study, I wanted to test the impact of different probe shapes, sizes, and measuring forces on the thickness readings delivered by the same measurement device. For this experiment, I used a Heidenhain MT-60 gauge (Figure 2). This gauge features motorized actuation, which made it easy to change the probe force and configuration.

Using the gauge, I took 16 readings from the 8 x 8-in. image area of 16 separate screens (Figure 3). The screens featured NBC monofilament polyester mesh with a thread count of 380 threads/in. and a thread diameter of 33 microns. The mesh on each screen was stretched equally along both the warp and weft directions to a tension level of 18 N/cm2. Assessing the Accuracy of Thickness-Measurement Tools

Figure 2 Thickness Gauge Contact-thickness gauges deploy their measuring probes in different ways, some using springs, others relying on pneumatic drives, and still others featuring electrically powered motors, such as the Heidenhain MT-60 shown here. The type of drive system affects the amount of control the user has over probe force during the measurement process.

By Fernando Zicarelli, Dynamesh Inc.

In this test, I used four different probe shapes/sizes: 4.8 mm flat, domed, 1.5 mm flat (also called a pin probe), and round. With each of these probes, I applied three different gauge forces: 1, 1.25, and 1.75 N. The measurement values I obtained were recorded in an Excel spreadsheet for comparison purposes.


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