Chapter 10 Miscellaneous Types of Fasteners LOCK NUTS
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Chapter 10 Miscellaneous Types of Fasteners
LOCK NUTS and LOCKING DEVICES Many different locking devices are used to prevent nuts from working loose. A screw thread holds securely unless the parts are subject to impact and vibration (e. g. as in a car engine). A common device is the jam nut (A). Slotted nuts (L) and castle nuts (M), to be held with a cotter pin or wire, are commonly used in automotive industry. Round nut locked by means of setscrew is shown at B. A brass plug is placed under the setscrew to prevent damage to the thread. This is a common type of adjusting nut used in machine-tool practice. C is a locknut, in which the threads are deformed after cutting. D, E and F are spring washers, also commonly used for locking.
WASHERS Plain washers are commonly used in the assembly of nuts and bolts to provide a smooth surface for the nut or bolt to turn against. Specifications are given by inside dia. , outside dia. , thickness, type. For example, 1. 375 x 2. 500 x 0. 165 type A plane washer would be used with 1. 25 in. fastener (App. 27 A) Lock washers prevent a fastener from loosening due to vibration or stress. Spring washers (D, E, F) sometimes called tooth lock washers. G, H are thicker and known as helical-spring lock washers.
KEYS Key fasteners are used to prevent the rotation of wheels, gears etc. on their shafts. A key is a piece of metal placed so that part of it lies in a groove, called "key seat", cut in a shaft and part of it fits into a groove cut in a hub, called "key way". Therefore, after the assembly locked together by the key, the shaft and hub can not rotate relative to each other. .
KEY TYPES The simplest key is the square key, placed half in the shaft and half in the hub. A flat key is rectangular in cross section, used similarly as square key.
MISCELLANEOUS FASTENERS The gib-head key is tapered on its upper surface and is driven in to form a very secure fastening. The Pratt & Whitney key is rectangular in cross section and has rounded ends. It is placed two-thirds in the shaft one-third in the hub. The most common key is the Woodruff key. This key is flat segmental disk with a flat (A) or round (B) bottom.
SPECIFICATION OF KEYS Keys are specified by note or number depending on type. Ex: 1/2 *3/8 Flat key 2. 5 Lg Pratt and Whitney Key No. 6 DIMENSIONING FOR KEYS
For very heavy duty, keys are not sufficiently strong, splines (grooves) are cut in both shafts and hubs , arranged so that they fit one within other.
SPRINGS A spring can be defined as an elastic body designed to store energy when deflected. Springs are classified according to their geometric form: helical or flat.
SPRINGS TYPES OF SPRINGS
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