Machine Design (EML3500)

Course Description

Machine Design covers the design of machine elements including fasteners, bearings, gears, and other power transmission components.

Within the SCNS taxonomy, EML is the Mechanical Engineering prefix. The University of West Florida publishes this at 3 semester hours, prerequisites EGM3401, EML3011, and EML3172L, giving approximately 45 contact hours at the standard university lecture ratio.

This is where mechanical engineering becomes design rather than analysis. Every course up to this point has asked "what happens to this?"; machine design asks "what should this be?" — and the difference is that design problems have no single correct answer, only defensible ones. Students who have been rewarded for finding the right number find that disorienting, and adjusting to it is the real content of the course.

Learning Outcomes

Required Outcomes

• Describe the design process and the role of iteration, constraints, and trade-offs.
• Interpret a design requirement and convert it into engineering specifications.
• Select factors of safety appropriately and justify the choice.
• Apply static failure theories to ductile and brittle materials.
• Apply fatigue failure criteria, including endurance limit and modifying factors.
• Account for stress concentration in fatigue design.
• Apply mean stress correction using Goodman or equivalent relations.
• Design shafts for combined bending and torsion under fatigue loading.
• Select and specify threaded fasteners and calculate preload and joint stiffness.
• Analyze bolted joints under static and fatigue loading.
• Design and analyze welded and permanent joints.
• Select rolling element bearings using life and load rating calculations.
• Describe journal bearings and lubrication regimes.
• Analyze spur gears, including geometry, kinematics, and force analysis.
• Apply bending and surface durability criteria to gear design.
• Describe helical, bevel, and worm gears and their applications.
• Design and select belt, chain, and flexible power transmission elements.
• Design and select springs.
• Select clutches, brakes, and couplings.
• Apply tolerances and fits to designed components.
• Apply design for manufacturability and select appropriate processes.
• Use standard components and manufacturer catalogues in design.
• Document a design with calculations, drawings, and justification.
• Evaluate alternative designs and defend a selection.

Optional Outcomes

• Use finite element analysis to support design decisions.
• Apply reliability-based design methods.
• Describe design codes and standards applicable to machine elements.
• Describe product liability and engineering ethics in design.
• Perform a design project from specification through documentation.
• Relate content to the FE examination specification.

Major Topics

Required Topics

• The design process
• Requirements and specifications
• Factors of safety
• Static failure theories
• Fatigue failure criteria
• Stress concentration in fatigue
• Mean stress and the Goodman relation
• Shaft design
• Threaded fasteners and preload
• Bolted joint analysis
• Welded and permanent joints
• Rolling element bearing selection
• Journal bearings and lubrication
• Spur gear geometry and forces
• Gear bending and surface durability
• Helical, bevel, and worm gears
• Belts, chains, and flexible elements
• Spring design
• Clutches, brakes, and couplings
• Tolerances and fits
• Design for manufacturability
• Standard components and catalogues
• Design documentation
• Design evaluation and justification

Optional Topics

• Finite element analysis in design
• Reliability-based design
• Codes and standards
• Product liability and ethics
• Design project
• FE examination alignment

Resources & Tools

• Shigley's Mechanical Engineering Design (Budynas & Nisbett) — the machine design text, essentially universal, and the book practising designers keep.
• Machine Elements in Mechanical Design (Mott) — more approachable and strong on component selection.
• Fundamentals of Machine Component Design (Juvinall & Marshek) — the other standard.
• Machinery's Handbook — the machinist's reference; the fits, tolerances, thread, and gear tables are what industry actually uses.
• Manufacturer catalogues — free and essential: SKF and Timken for bearings, Boston Gear and Martin for gears and chain, Gates for belts, Associated Spring for springs. Real design is done from these, and learning to read a bearing life calculation from SKF's own method is directly employable.
• NCEES FE Reference Handbook — free; the machine design section is examined.
• ANSI/AGMA standards for gears and ASME standards for shafts and pressure components — the operative documents in industry.
• SolidWorks, Inventor, or Fusion 360 — for the drawings and the assembly; Fusion 360 has a free personal tier and Autodesk provides free education licences.
• Excel or Python — machine design is iterative, and a spreadsheet that recalculates a shaft design when a dimension changes is how the work is actually done.
• eFatigue and MatWeb — free fatigue and material property references.

Career Pathways

• Mechanical design engineer — SOC 17-2141; this course is the closest thing in the curriculum to the actual job.
• Product design engineer.
• Machine and equipment designer — industrial machinery, packaging, and automation.
• Powertrain and drivetrain engineer.
• Aerospace mechanical systems engineer — Florida's Space Coast, Melbourne, and Orlando defence sector.
• Manufacturing engineer — tooling, fixtures, and process equipment.
• Reliability engineer — bearing and gear life prediction is the technical core.
• Applications engineer for bearing, gear, and drive manufacturers — a well-paid role that uses exactly this material.
• Marine and boat systems engineer — a Florida specialization.
• Forensic engineering — machine failure investigation.
• Licensed professional engineer — machine design appears on the FE Mechanical and is the basis of the PE Mechanical Machine Design and Materials depth exam.

Special Information

⚠ Design problems have no single right answer — and that is the point

• Analysis has one answer; design has a defensible range. Two competent engineers will size the same shaft differently and both can be correct, and being graded on justification rather than on matching a key is the adjustment students find hardest.
• State your assumptions and your reasoning. The calculation is worth less than the argument for why you chose that load case, that material, that safety factor, and that standard component.
• Iterate. First-pass designs are wrong, and the process is: assume, calculate, check, revise. Students who try to get it right in one pass stall.
• Use standard components wherever possible. A catalogue bearing is cheap, available, and has published life data; a custom equivalent is none of those.
• Design to the manufacturer's method. Bearing life, gear rating, and belt selection all have published procedures, and using them is correct practice rather than a shortcut.
• Sanity-check dimensions physically. A shaft calculated at 3 mm diameter for a 50 kW drive means an error somewhere.
• Document as you go. A design you cannot explain in six months is a design nobody can maintain.
• The FE and PE examinations test the analysis; employers test the judgement. Build both.

⚠⚠ Fatigue is the failure mode machine design exists to prevent

• Rotating and reciprocating machinery fails by fatigue, not by overload. The part was strong enough for the static load and failed anyway after many cycles — which is why static strength calculation alone is insufficient for anything that moves.
• Endurance limit is modified, not used raw. Surface finish, size, loading type, temperature, and reliability factors all reduce it, and the modifying factors are where the real design work is.
• Stress concentrations dominate fatigue life. Fillets, holes, keyways, threads, and shoulders are where cracks start — a generous fillet radius is one of the highest-value and cheapest design decisions available.
• Mean stress matters. A fully reversed load and a fluctuating load with the same amplitude behave differently, and the Goodman relation exists to handle it.
• Surface treatment extends life substantially — shot peening and induction hardening introduce compressive residual stress exactly where cracks would start.
• Aluminium has no endurance limit. Steels can be designed for infinite life; aluminium alloys must be designed for a finite number of cycles, and this distinction has real aerospace consequences.
• Fatigue data scatters widely, which is why reliability factors exist and why the design values are conservative.
• Look at real failures. A fractured shaft with beach marks radiating from a keyway teaches the lesson permanently — see this repository's EML3172L guide on reading fracture surfaces.

⚠ Bolted joints are harder than they look

• A properly designed bolted joint carries fluctuating load largely in the clamped members, not in the bolt — which is why preload is the design variable and why an under-tightened bolt fails in fatigue while a correctly tightened one does not.
• That is genuinely counterintuitive: tightening a bolt more makes it experience less cyclic stress, provided the joint does not separate.
• Joint stiffness ratio determines the load split, and calculating member stiffness is the part students skip.
• Torque is a poor proxy for preload. Most of the applied torque overcomes friction, and the friction coefficient varies enormously with lubrication and surface condition — which is why critical joints use turn-of-nut, tension indicators, or direct measurement.
• Bolts loosen under vibration, and thread-locking, prevailing-torque nuts, and correct preload all address it.
• Do not mix grades carelessly, and know that a higher-grade bolt is not automatically better in a fatigue application.
• Gasketed joints behave differently because the gasket dominates member stiffness.
• Specify the tightening method on the drawing, not just the fastener — a correctly designed joint assembled wrongly is an incorrectly designed joint.

⚠ An honest account of the workload

• Upper-division mechanical engineering courses demand sustained daily problem-solving and reward nothing else. Budget eight to twelve hours a week outside class.
• Work problems without the solution visible. Reading a worked example produces the feeling of understanding and none of the ability.
• Draw the diagram every time — free-body, control volume, thermal resistance network, or block diagram.
• State your assumptions explicitly. Steady state, incompressible, adiabatic, linear elastic, small angle — knowing which assumptions apply is most of the subject.
• Carry units through every step and check that the answer is physically plausible.
• Go to office hours in week two, not week ten. These courses are cumulative.

⚠ Institutional context — and check the number against the description

• This guide is written primarily from the University of West Florida catalog, which publishes a complete and unusually explicit set of EML entries. Other Florida institutions teaching this subject may number it differently.
• The EML prefix is not consistent across Florida. This repository has documented a genuine subject collision in the thermal-fluids sequence: EML3015 and EML3016 denote different subjects at UWF and at the FAMU-FSU College of Engineering — see the EML3015C and EML3016 guides.
• Much of the mechanical engineering core is also taught under the general engineering prefix EGN, and under SCNS those are different courses. Equivalency does not cross prefixes or a C or L suffix automatically.
• Identify a course by its catalog description, never by its number or its title.
• Give a receiving department the description rather than the course number when seeking a transfer determination, and get the answer in writing.

⚠ FE exam and PE licensure — this is the accredited engineering pathway

• This course sits inside an A.B.E.T.-EAC accredited engineering programme, the pathway that leads directly to professional licensure. That distinguishes it from engineering technology, where the route to a P.E. is longer — see this repository's ETG, EET, and ETC guides.
• Florida licenses professional engineers under Chapter 471, Florida Statutes, through the Florida Board of Professional Engineers: A.B.E.T.-EAC degree → FE examination → qualifying experience → PE examination → licensure.
• The NCEES FE Reference Handbook is free and is the only reference permitted in the exam. Use it as your working reference now so navigating it is automatic by exam day.
• Most students sit the FE in their final year, and pass rates are markedly higher for recent graduates than for those who wait.
• Only a licensed P.E. may offer engineering services to the public in Florida, seal drawings, or use the title in a way implying licensure.
• Rule 11 applies — verify current requirements with FBPE and NCEES directly.

How Florida course levels affect transfer

The first digit of an SCNS number denotes the year of offering, not transferability. Courses at the 1000 and 2000 levels transfer transparently between Florida public institutions, and 3000 to 4000 is unproblematic since both are upper division. The boundary that actually matters is 2000 to 3000, where lower-division credit generally cannot satisfy an upper-division requirement.

EML3500 is 3 semester hours and approximately 45 contact hours. Expect design problems and probably a design project rather than examinations alone, with assessment weighted toward justification and documentation.

Keep Shigley. It is one of the few undergraduate textbooks that practising engineers genuinely keep on the shelf, and the tables and procedures are used in industry exactly as they are used in the course. This subject also appears under EML4501, EML4507, and various EGN numbers at other Florida institutions.