Circular & Total Runout

Geometric Tolerancing Geometric Tolerancing is used to specify the shape of features. Things like: •Straightness •Flatness •Circularity •Cylindricity •Angularity •Profiles •Perpendicularity •Parallelism •Concentricity •And More... Geometric Tolerances are shown on a drawing with a feature control frame. Runout is specified on cylindrical parts. It is measured by placing a gage on the part, and rotating the part through 360 degrees. The total variation is recorded as the runout. • Circular runout is measured at one location. • Total Runout is measured along the entire specified surface. Principles of Engineering Drawing Thayer Machine Shop

Gear Types

The most common types of gears are illustrated in Figs. 5.16 to 5.25. Other available types are generally modifications of the basic gears shown. Gear nomenclature and definitions can be found in ANSI/AGMA 1012-F90, Gear Nomenclature, Definitions of Terms with Symbols.1 Spur gears A spur gear has a cylindrical pitch surface and teeth that are parallel to the axis. Spur gears operate on parallel axes (Fig. 5.16). Spur rack A spur rack has a plane pitch surface and straight teeth that are at right angles to the direction of motion (Fig. 5.16). Helical gears A helical gear has a cylindrical pitch surface and teeth that are helical. Parallel helical gears operate on parallel axes. Mating external helical gears on parallel axes have helices of opposite hands. If one of the mating members is an internal gear, the helices are of the same hand (Fig. 5.17). Single-helical gears Gears have teeth of only one hand on each gear (Fig. 5.18). Double-helical gears Gears have both right-hand and left-hand teeth on each gear. The teeth are separated by a gap between the helices (Fig. 5.19).Where there is no gap, they are known as herringbone gears. Wormgearing Includes worms and their mating gears. The axes are usually at right angles (Fig. 5.20). Wormgear (wormwheel) The gear that is the mate to a worm. A wormgear that is completely conjugate to its worm has a line contact and is said to be enveloping. An involute spur gear or helical gear used with a cylindrical worm has point contact only and is said to be nonenveloping (Fig. 5.20). Cylindrical worm A worm that has one or more teeth in the form of screw threads on a cylinder. Enveloping worm (hourglass) A worm that has one or more teeth and increases in diameter from its middle portion toward both ends, conforming to the curvature of the gear (Fig. 5.20). Double-enveloping wormgearing This is comprised of enveloping (hourglass) worms mated with fully enveloping wormgears (Fig. 5.21). Bevel gears These are gears that have conical pitch surfaces and operate on intersecting axes that are usually at right angles (Fig. 5.22). Miter gears These are mating bevel gears with equal numbers of teeth and with axes at right angles (Fig. 5.23). Straight bevel gears These have straight tooth elements which, if extended, would pass through the point of intersection of their axes (Fig. 5.24). Spiral bevel gears These have teeth that are curved and oblique (Fig. 5.24). Hypoid gears Similar in general form to bevel gears, hypoid gears operate on nonintersecting axes (Fig. 5.25). 

Standard Handbook of Plant Engineering (3rd Edition)

By: Rosaler, Robert © 2002 McGraw-Hill
Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)

Design Procedure for Crankshaft

The following procedure may be adopted for designing a crankshaft. 1. First of all, find the magnitude of the various loads on the crankshaft. 2. Determine the distances between the supports and their position with respect to the loads. 3. For the sake of simplicity and also for safety, the shaft is considered to be supported at the centres of the bearings and all the forces and reactions to be acting at these points. The distances between the supports depend on the length of the bearings, which in turn depend on the diameter of the shaft because of the allowable bearing pressures. 4. The thickness of the cheeks or webs is assumed to be from 0.4 ds to 0.6 ds, where ds is the diameter of the shaft. It may also be taken as 0.22D to 0.32 D, where D is the bore of cylinder in mm. 5. Now calculate the distances between the supports. 6. Assuming the allowable bending and shear stresses, determine the main dimensions of the crankshaft. Notes: 1. The crankshaft must be designed or checked for at least two crank positions. Firstly, when the crankshaft is subjected to maximum bending moment and secondly when the crankshaft is subjected to maximum twisting moment or torque. 2. The additional moment due to weight of flywheel, belt tension and other forces must be considered. 3. It is assumed that the effect of bending moment does not exceed two bearings between which a force is considered. 

FIRST MULTICOLOUR EDITION

(S.I. UNITS)

[A Textbook for the Students of B.E. / B.Tech.,

U.P.S.C. (Engg. Services); Section ‘B’ of A.M.I.E. (I)]

A TEXTBOOK OF

Machine Design

R.S. KHURMI

J.K. GUPTA

What Are Titanium Alloys?

For purposes of this chapter titanium alloys are those alloys of about 50% or higher titanium that offer exceptional strength-to-density benefits plus corrosion properties comparable to the excellent corrosion resistance of pure titanium. The range of operation is from cryogenic temperatures to around 538–595 C (1000–1100 F). Titanium alloys based on intermetallics such as gamma titanium aluminide (TiAl intermetallic compound which has been designated ) are included in this discussion. These alloys are meant to compete with superalloys at the lower end of superalloy temperature capability, perhaps up to 700 C ( 1300 F). They may offer some mechanical advantages for now but often represent an economic debit. Limited experience is available with the titanium aluminides. Temperature Capability of Titanium Alloys Although the melting point of titanium is in excess of 1660 C (3000 F), commercial alloys operate at substantially lower temperatures. It is not possible to create titanium alloys that operate close to their melting temperatures. Attainable strengths, crystallographic phase transformations, and environmental interaction considerations cause restrictions. Thus, while titanium and its alloys have melting points higher than those of steels, their maximum upper useful temperatures for structural applications generally range from as low as 427 C (800 F) to the region of about 538–595 C (1000–1100 F) dependent on composition. As noted, titanium aluminide alloys show promise for applications at higher temperatures, perhaps up to 700 C ( 1300 F), although at one time they were expected to offer benefits to higher temperatures. Actual application temperatures will vary with individual alloy composition. Since application temperatures are much below the melting points, incipient melting is not a factor in titanium alloy application. 

SELECTION OF TITANIUM ALLOYS

FOR DESIGN

Matthew J. Donachie

Rensselaer at Hartford

Hartford, Connecticut

Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.

Edited by Myer Kutz

by John Wiley & Sons, Inc.