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Sometimes, You Just Gotta Be Direct

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A big advantage of hydraulics over other forms of power transmission is how easy it is to measure applied force from a hydraulic cylinder. For best results, just install a pressure gauge or pressure transducer on the high-pressure side of the cylinder, and you’re in business. Taking the pressure readout and figuring in the piston area gives a pretty good measure of output force.

But sometimes “pretty good” isn’t good enough. Depending on the size, material, and geometry of the piston and rod seals, friction can introduce error into the calculation. The type of fluid and even temperature can also come into play. And don’t forget about error of the measuring device itself.

The Force GaugeThe Force Gauge, from American Workholding Inc., indicates force applied to a work piece, rather than by measuring hydraulic pressure of the cylinder. The result is a more precise and repeatable representation of force, without expensive and complex electronic instrumentation.

Any one of these sources of error may seem negligible by itself, but accounting for them collectively could make a difference—especially when it comes to repeatability. Test readings today might differ from what they were yesterday, even though readout of cylinder pressure may be the same.

One way to account for all these parameters would be to purchase, install, and calibrate more instruments. However, a simpler and less-expensive solution would be to measure force from the piston rod directly. Doing so takes friction, temperature, and other parameters out of the equation. One such device for measuring compression force from a cylinder—or machine screw, ball screw or any other linear actuator for that matter—is the Force Gauge, recently introduced by American Workholding Inc., Cincinnati.

The Force Gauge measures and displays compressive force in lb on a large-diameter, easy-to-read gauge and is designed for use in shop environments. The handheld instrument has an anodized aluminum body and a hexagonal outer surface so it can accommodate 2- and 3-point force readings.

Bernard Varnau, president of American Workholding, said he developed the Force Gauge as a quick and easy way to know exactly the clamping force in a 3-jaw lathe chuck setup. “I became frustrated with the pressure gauges on machine tools that did not deliver a close, repeatable value immediately at the jaw/part contact point. This feature alone saves time and money due to less scrap, and very quick re-setup of a repeating job, where an out-of-round condition is not acceptable.”

The force Gauge has ½-13 tapped holes on each of its six faces to allow direct, static mounting at the end of a hydraulic press arbor. It comes in three ranges for measuring 0 to 1,000, 0 to 5,000, and 0 to 15,000 lb.

For more information, contact Varnau at (513) 720-9571 or via e-mail.

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