Machine design Basics - I - Shaft, Bearings & Gears

Learn general layout schemes for a machine shop, focusing on the concept phase to plan shaft layouts for mounting gears, bearings, and pulleys with proper axial location.

Develop the concept layout for a shaft assembly by locating gears, pulleys, bearings, and housing, minimizing overhangs, keeping loaded components close to bearings, and evaluating multiple layout options.

Examine mounting provisions that secure shaft-mounted components with keys and keyways. Understand stress concentration, shear and crushing failures, and design equations for safe torque transmission using Woodruff and other keys.

Explore set screws with collars that clamp a pulley to a shaft, defining holding power and clamping force for low-load applications, while noting loosening under vibration.

Explore splines and serrations for mounting shafts to hubs, including axial slip and planes vs cetaceans, with ISO 5-4-8-1 guidance for design.

Pins fasten gears to shafts by passing through aligned holes, delivering a snug fit and higher torque transfer, suitable for low power, low speed, and intermittent rotation.

Explore press fits and interference fits for mounting bearings and components on shafts, and learn how shaft-hub tolerances and friction govern holding power and assembly strength.

Analyze shaft stresses by constructing a free-body diagram, evaluating bending and torsional stresses from loads, and applying stress concentration factors to ensure safe shaft design.

Design a shaft with an integral gear, analyze radial and tangential loads and bearing reactions, and compute the maximum bending moment in two mutually perpendicular planes and the resultant moment.

Explore mean and alternating stresses in rotating shafts from bending and torsion, and apply von Mises fatigue theory to assess failure under fluctuating loads.

Explore how changing cross-sections create stress concentration in shafts under bending and torsion, and how taper transitions and flat radii smooth stress lines with theoretical factors (Kt) for load cases.

This lecture examines notch sensitivity and fatigue stress concentration factors, showing how sharp shaft transitions reduce fatigue life and how material type governs q and k in bending and torsion.

Apply stress concentration factors from the Katie and kids graphs to this shaft and gear problem, determining Kt and fatigue stress concentration factor using notch radius and Q for design.

explain fatigue endurance limit and how to modify it for a shaft using surface, size, load, temperature, and reliability factors, applying the distortion energy theory and the fatigue life graph.

Apply the Goodman fatigue criterion using the endurance limit and ultimate tensile strength to plot the Goodman line and assess fatigue safety and factor of safety.

Explore design changes to shaft and bearing assemblies to boost the factor of safety by increasing diameter, upgrading material, and reducing stress concentration, using the design equation for fatigue.

Assess stress concentration factors for preliminary shaft design, focusing on sharp shoulders and steps relevant to fatigue loading, and reduce them with rounding, undercut relief, and smooth stress flow.

Analyze deflection and slope of a centrally loaded simply supported shaft by deriving slope and deflection diagrams from the bending moment diagram, and check against bearing tolerances and gear misalignment.

Analyze critical speeds and resonance in rotating shafts, noting multiple modes and how attachments such as gears and bearings affect them, and emphasize calculating the natural frequency to avoid resonance.

Explore how interference fits between shafts and hubs generate radial and tangential stresses, calculate maximum and minimum interference, and assess their impact on torque transfer, stress concentration, and fatigue.

Assess the torque capacity of an interference fit by analyzing friction at the shaft–hub interface, using normal force and radius to prevent slip under worst-case conditions.

Compare solid and hollow shafts: hollow designs reduce weight for the same outer diameter, and can match inertia by increasing the bore, achieving about 22 percent weight savings.

Learn to connect shafts with couplings, manage radial, axial, and angular misalignment, and compare rigid, flexible, universal, Oldham, drag, and gear couplings for various torque and environmental conditions.

Learn how to select bearings for shafts, from plain bushings to fluid and rolling contact bearings, balancing space, loads, speed, lubrication, life, and misalignment in design.

Explore the factors driving bearing selection in machine design, including loads, speed, packaging, life, friction, lubrication and sealing, tolerances, assembly, temperature, contamination, materials, and misalignment.

Learn about rolling bearing types, including deep groove, angular, self-aligning, needle, cylindrical, tapered, spherical, and thrust bearings, and how radial, axial, and misalignment loads shape their use.

Compare major bearing types by radial load bearing ability, axle load bearing ability, moment loads, misalignment tolerance, friction, stiffness, and high-speed suitability.

Identify the primary causes of bearing failure, focusing on metal fatigue due to contact stresses at ball/roller–race interfaces, and the role of contamination, lubrication, misalignment, corrosion, and manufacturing defects.

Explain contact stresses at curved surfaces, forming hemispherical pressure distributions and the maximum B max in ball bearings and roller contacts, and how larger contact areas reduce stress.

Derive bearing life by using rating life and basic load rating with the application load, guided by ISO 281, to estimate L10 life and 90 percent reliability from catalog data.

Learn how bearing life, based on catalog rating, is modified by life adjustment factor A1, reliability, contamination, lubrication, misalignment, and mounting conditions.

Explore how lubricant viscosity and the viscosity ratio influence bearing life by using a viscosity-ratio graph to determine the life modification factor under varying temperatures.

Determine the equivalent bearing load by combining radial and axial components using VFR criteria. Extract X, Y, and C_not values from manufacturer catalogs to compute P.

Assess the maximum axial load the bearing can tolerate and compute the minimum radial load with the formula, applying preloading when the radial load falls short.

Select an SKF deep groove ball bearing for a 30 bore and 42 od using the SKF catalog to meet 1000 N radial load, 500 rpm, and 15000 h life.

Determine viscosity ratio and reference kinematic viscosity from grease specifications, then apply life modification factor and contamination factor to predict bearing life and guide selection.

Explains how lubrication forms an elastic film to prevent metal contact. Covers viscosity effects, heat dissipation, corrosion protection, and grease versus oil choices for bearings.

Explore mounting schemes for bearings between a shaft and housing, including floating bearings, shoulders, retaining rings, and end plates to control axial location while simplifying assembly.

Explain the conjugate action of gearing, where two gears maintain a constant velocity ratio via rolling contact along a fixed line of action at the pitch point.

Learn how the involute profile ensures conjugate gear action with a constant line of action by unwrapping a taut string from a base circle and constructing tangents.

Create the involute profile in CAD using Fusion 360, applying constraints, equal segments, and tangent relations to a circle, then refine with through-dimension measurements for accuracy.

Explore spur gear design basics, including pitch circle, base circle, pitch diameter, addendum, dedendum, clearance, backlash, circular pitch, module, and the pressure angle.

Learn a CAD-based spur gear design workflow in Fusion 360, from input speed and gear ratio to creating pinion and driven gear profiles with addendum, pitch circles, and patterns.

Learn how to compute the contact ratio by analyzing the contact angle, angle of approach, and angle of recess, using addendum circles, line of action, and length of engagement.

Explore interference in gear design, how addendum and base circle geometry affect contact along the pressure line, and determine minimum teeth to avoid interference under design and manufacturing variations.

Increase teeth count, raise the pressure angle, apply undercutting, or reduce addendum coefficient to avoid interference, and manage backlash as gear clearance measured by dial indicators and slip gauges.

Learn how helical gears use helix angle for smoother, quieter operation and better stress distribution, with key design parameters like transverse and normal circular pitch and lead.

Design a helical gear in CAD by creating a reference profile and pitch line, mirroring, applying a circular pattern, and sweeping a 22-degree twist to form the solid gear.

Apply the Treadgold approximation to generate gear profiles, sweep the profile through the intersection point, cut the addendum cone, and pattern it for 20 instances to finalize the gear.

Bevel gear design workflow part 1 guides setting input data, sketching pinion and driven gears, and applying treadgold approximation to determine pitch diameter and base circle.

Center bevel gear profiles on the pitch line, ensure symmetry with tangents and construction elements; loft, revolve addendum, then pattern and boolean-cut to complete the gear.

Explore worm gearset design basics for high gear ratios and sliding contact. Learn lead angle, axial pitch, circular transverse pitch, starts, and the worm gear pitch diameter.

Design a worm gearset in CAD using Indian values, determining the reference diameter, axial pitch, and lead angle to create the worm profile and sweep it for proper engagement.

Design a worm gearset in CAD by defining pitch and root cylinders, then model the worm wheel as a 30-tooth helical gear with 150 mm pitch diameter.

Execute the worm gearset design workflow in CAD part 3 by using addendum circle profiles, extruding, and circular patterning around the cylinder axis, then compute the twist angle for sweep.

Analyze spur gear force analysis by resolving contact into radial and tangential components at the pressure angle, establish equilibrium, and relate tangential force to torque, pitch line velocity, and efficiency.

perform spur gear force analysis by calculating transmitted load from 1 kW at 1000 rpm with a 200-tooth gear and determine gear reactions via pressure angle and force triangle.

Analyze 3D force in bevel gears by decomposing the resultant W into tangential W_T, radial W_R, and axial W_E components along X, Y, Z, using delta for plane projections.

explain bevel gear force analysis by deriving the average radius RTV from the gear cone geometry and relating the tangential force W.T to RTV and the cone angle Delta.

Analyze the forces on a helical gear by resolving the resultant W into tangential, radial, and axial components, using helix and pressure angles to define the normal and transverse pressures.

Analyze worm gear force components W, X, Y, Z, and the axial, tangential, and radial forces; incorporate lead angle lambda and sliding friction to derive efficiency.

Analyze gear tooth durability and failure modes, including jamming, loss of motion, bending stress, crack propagation, surface wear, and scoring or abrasion from lubrication failure.

Apply the Lewis bending equation to estimate gear tooth bending stress from tangential load, considering tooth geometry, pitch line velocity, the dynamic factor, and the factor of safety.

Explains gear surface damage from high contact stresses using Hudson contact mechanics, modeling teeth as cylinders to compute max contact pressure from local radii of curvature and material properties.

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