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Glossary
Posted August 22, 2019 - Updated Dec 12, 2019
Acme Screws A screw thread series first developed in 1895 to replace square threads for use in positioning and power transmission. Acme screws are the most widely used power screws, popular in all industries for linear motion. See the Acme section for more information. Backdrive The action of converting thrust to torque, common to bearing […]
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Screw Thread Pitch
Posted August 22, 2019 - Updated Dec 3, 2019
Identifying Thread Pitch The thread pitch can be measured with a steel rule, as illustrated in Figure 44, or a caliper or comparator can be used. The thread pitch is the axial distance from one thread groove to the next. By laying a steel rule down the axis of a screw and counting the number […]
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Screw Thread Form
Posted August 22, 2019 - Updated Dec 3, 2019
Identifying Thread Form There are many different thread forms in use today. The forms most widely used for power transmission screw threads are illustrated in Figure 43. An optical comparator is the easiest method of determining thread form. Profile gages, if available, and visual methods can also be used. Great care must be taken as […]
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Hand of the Thread
Posted August 22, 2019 - Updated Dec 3, 2019
Identifying Hand of the Thread The hand of the thread can be easily determined by visual inspection. Simply compare your screw threads with the right hand and left-hand threads illustrated in Figure 48. Most threads are right hand and right hand is assumed if no left-hand designation is specified. Left-hand threads are common on manual […]
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Pitch Diameter
Posted August 22, 2019 - Updated Dec 3, 2019
Identifying Pitch Diameter The pitch diameter is the diameter at which the thread tooth and the thread space are equal. To accurately measure the pitch diameter requires an optical comparator or thread wires. The optical comparator is the easiest to use as the measurement can be directly made and no mathematics is necessary. The disadvantage […]
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Major & Minor Diameter
Posted August 22, 2019 - Updated Dec 3, 2019
Identifying Major Diameter The major diameter can be measured with a micrometer, caliper or steel rule. Major diameters are generally the first numbers found in thread designations. A 1/2-10 Acme thread, for example, has a major diameter of .500 in. Care must be taken to measure the major diameter on a section of the screw […]
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Identifying Screw Threads
Posted August 22, 2019 - Updated Dec 3, 2019
How To Identify Screw Threads With the information provided in this section, users can readily identify most thread forms. To accomplish this, the features in the list below must be determined. Frequently, it is necessary to identify threaded parts in the field in order to properly select replacement parts and to choose the right type […]
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Wear Equations
Posted August 22, 2019 - Updated Dec 4, 2019
Wear Equations As discussed earlier, estimating the service life of Power Screw systems is a very complex task and inexact at best. The only reliable predictor is actual testing. Variations in service life are widely scattered and multiples of two to one or three to one in life test performance are not uncommon. The field […]
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Monitoring Wear
Posted August 22, 2019 - Updated Dec 4, 2019
Wear Life Testing Methods As mentioned before the best method of assessing the performance and life of Power Screws and nuts is actual field testing. This may present difficulties because of time constraints so accelerated lab testing is often conducted instead. When monitoring wear, all lab testing should monitor drive torque and nut temperature along […]
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Screw and Nut Material Selection
Posted August 22, 2019 - Updated Dec 4, 2019
Screw and Nut Material Selection To reduce the costs of wear in Power Screw systems, we recommend designs where nuts are made of softer material and screws of a harder material. This ensures that the nuts will wear and the screw will remain relatively wear-free, which is desirable because replacement nuts are usually much less […]