Mechanical Design Handbook

Friction, Laws of Friction, and Rolling Resistance Friction is the resistance to motion that occurs when one body moves upon another. It is defined as the force acting at the surfaces of contact that resists relative sliding. For sliding motion, the friction force F is proportional to the normal force N . This relationship is expressed by the coefficient of friction, denoted by μ : F = μ × N μ = F / N Example: A body weighing 28 lb rests on a horizontal surface. If a force of 7 lb is required to keep it in motion: μ = 7 / 28 = 0.25 Angle of Repose When a body rests on an inclined plane, friction prevents it from sliding until a critical angle is reached. This angle is called the angle of repose , denoted by θ. At this condition: μ = tan θ The angle of repose provides a practical experimental method for determining the coefficient of friction between two surfaces. A greater force is required to start motion than to maintain it, because static ...

Source: Google Book Many engineering applications require high surface hardness to resist wear, while complex service conditions demand adequate core strength and toughness to withstand impact and cyclic loading. To obtain this combination of properties, two general approaches are commonly used: 1) Modifying the chemical composition of the surface layer before or after quenching and tempering. Common methods include carburizing, nitriding, cyaniding, and carbonitriding. 2) Hardening only the surface layer by localized heating followed by rapid quenching. The most widely used techniques are flame hardening and induction hardening. Carburizing: Carburizing is a thermochemical process in which carbon is diffused into the surface of a steel component to a controlled depth by heating it in a carbon-rich environment. The hardened surface layer, known as the case, provides high wear resistance while maintaining a tough, ductile core. Case depth depends on the carbon potent...

Hardenability, Quenching Media, and Tempering of Steel Hardenability is a fundamental property of steel that describes its ability to develop hardness to a specified depth when quenched from the austenitizing temperature. It should not be confused with hardness or maximum hardness . Hardness is a measure of resistance to indentation (Brinell, Rockwell, Vickers, etc.), whereas maximum attainable hardness depends almost entirely on carbon content. Maximum hardness is achieved only when the cooling rate during quenching is sufficiently rapid to produce a fully martensitic microstructure. While surface hardness is influenced by both carbon content and cooling rate, the depth over which hardness is maintained is governed by the steel’s hardenability. Hardenability is primarily controlled by alloying elements, but it is also affected by austenite grain size, austenitizing temperature and time, and the prior microstructure. The level of hardenability required for a component depen...

Working Model – Conceptual CAE & 2D Motion Simulation Software Working Model is one of the world’s most popular CAE (Computer-Aided Engineering) tools for conceptual design and motion simulation. It allows engineers to create accurate simulations that replace vague, time-consuming, and often inaccurate “back-of-the-envelope” calculations. Adopted by thousands of professional engineers worldwide, Working Model is used to create and analyze real-life mechanical systems. It was designed from the ground up to optimize performance on Windows-based operating systems and includes advanced features such as automatic collision detection and response for NURBS geometry . The software also includes powerful built-in scripts such as Flexbeam , Shear and Bending Moment , and Pin Friction , significantly expanding its capability for mechanical system analysis. At every stage of the product development cycle, Working Model helps engineers do more in less time. What once took d...

The Workhorse of Industry: V-Belt Drive Design Belt drive fundamentals explained for mechanical engineers, covering V-belts, pulley ratios, belt tension, wrap angle, stress factors, and practical design guidelines. 1. The Fundamentals A belt is a flexible power transmission element that seats tightly on a set of pulleys or sheaves . When used for speed reduction , the typical case, the smaller sheave is mounted on the high-speed shaft (e.g., an electric motor), while the larger sheave is mounted on the driven machine. The belt is designed to ride around the two sheaves without slipping. The belt is installed by placing it around the sheaves while the center distance is reduced. The sheaves are then moved apart, placing the belt under an initial tension. When power is transmitted, friction causes the belt to grip the driving sheave, creating a higher tension on the tight side . The opposite side carries a lower tension and is called the slack side ...

Flexible couplings and universal joints explained for mechanical power transmission, covering misalignment types, angular velocity variation, and practical engineering limits. Flexible Couplings .—Shafts that are out of alignment ( misalignment ) either laterally or angularly can be connected using various designs of flexible couplings . These couplings also allow a limited amount of axial movement in one or both shafts. Some flexible couplings transmit torque through disks or diaphragms. A simpler design consists of two flanges connected by links or endless belts made from leather or other strong, pliable materials. In other designs, the flanges contain projections that engage molded rubber or elastomeric elements to accommodate uneven motion between shafts. More advanced flexible couplings use toothed flanges that mesh with correspondingly toothed elements, allowing relative movement while maintaining torque transmission. Such couplings generally require lubrica...

CAD/CAM — In engineering, CAD stands for computer-aided design , which uses computer graphics systems to develop mechanical, electrical/electronic, and architectural designs. The term CADD (computer-aided drafting and design) is sometimes used to emphasize drafting and drawing functions. CAD technology forms the foundation for a wide range of engineering activities, including design, drafting, analysis, and manufacturing. Drawings developed during the design phase are often reused for analysis and optimization, creation of part and assembly drawings, and generation of NC/CNC programs for machining. Historically, once a component was designed using CAD, the design was passed to a part programmer who manually created machining programs. This process often required re-defining and re-entering geometry, leading to inefficiencies. This stage was commonly referred to as CAM ( computer-aided manufacturing ). Today, CAM encompasses a much broader scope, including fac...

Rolling Contact Bearings (Anti-Friction Bearings) Rolling contact bearings use rolling elements—either balls or rollers—to carry applied loads with very low friction. Unlike hydrodynamic or hydrostatic bearings, rolling contact bearings do not rely on a fluid film to separate surfaces, allowing them to operate with minimal wear and reduced starting torque. Because of their greatly reduced starting friction compared to conventional journal bearings, rolling contact bearings are commonly referred to as anti-friction bearings . They are typically manufactured with hardened rolling elements and raceways, and most designs use a separator (cage) to maintain spacing and minimize friction. Many variations are used throughout the mechanical and electrical industries. Common Applications The most widely used anti-friction bearing is the deep-groove ball bearing , usually supplied with a ribbon-type cage and sealed or shielded grease lubrication. This bearing is capable of suppor...

The Engineer's Guide to Roller Chain Drives A chain is a power transmission element made as a series of pin-connected links. Unlike belts, chains provide a positive engagement (no slip) and can transmit massive tensile forces. When transmitting power between rotating shafts, the chain engages mating toothed wheels called sprockets . The most common type is the Roller Chain . A hardened steel roller on each pin allows the chain to roll seamlessly into the sprocket teeth, reducing friction and wear significantly compared to bushing chains. Shop Heavy Duty Chain Breaker Tools 1. Decoding the Numbers: ANSI Standard Sizes Standard roller chains (ANSI B29.1) are designated by a number system that tells you the pitch instantly. Rule of Thumb: The digits (excluding the final zero) indicate the pitch in eighths of an inch . No. 40: 4/8" = 1/2 inch pitch No. 80: 8/8" = 1.0 inch pitch No. 200: 20/8" = 2.5 inch pi...