Design of Machine Elements

Course Description

Design of Machine Elements covers the design of fundamental machine components, including cams, gears, bearings, and couplings, with consideration of loads, stresses, and material strength characteristics.

Within the SCNS taxonomy, ETM is the Engineering Technology Mechanical prefix. Daytona State publishes this at 3 credits, offered spring, with PHY1053C or PHY2048C, and MAC2311C or EGN2045, as prerequisites. ⚠ The single term of offering is worth planning around.

This is the course where analysis turns into design, and the difference is that design problems have no single right answer. Analysis asks what stress a given shaft experiences; design asks what shaft to use, and the answer depends on load, life, cost, material availability, manufacturability, and what happens if it fails. The most important idea in it is fatigue — because the great majority of machine components that fail in service fail at stresses well below the strength the material data sheet advertises.

Daytona State does not publish a lecture and laboratory split for this course. Its engineering technology lecture courses run at the standard 15 contact hours per credit — ETG2520 (Statics) and EGN3311 (Statics) are both live at 3 credits and 45 hours — while the C-suffixed courses in these prefixes run at 20 (ETD2320C at 4 credits and 80 hours; ETD2364C, ETS2542C and ETS3543C all at 3 and 60). This course is unsuffixed and lecture-based, and is priced at the lecture convention.

Learning Outcomes

Required Outcomes

• Describe the design process and distinguish it from analysis.
• Identify loads acting on a machine component.
• Compute stresses from combined loading.
• Apply failure theories for static loading.
• Distinguish ductile and brittle failure criteria and select appropriately.
• Describe fatigue and cyclic loading.
• Interpret an S-N curve and describe the endurance limit.
• Apply modifying factors for surface, size, loading, and reliability.
• Compute fatigue factor of safety for a component.
• Identify stress concentrations and compute their effect.
• Describe notch sensitivity.
• Select and justify a factor of safety.
• Select materials based on strength, cost, and manufacturability.
• Design a shaft for strength, deflection, and fatigue.
• Select and size keys, splines, and shaft connections.
• Select rolling element bearings using life calculations.
• Describe journal bearings and lubrication.
• Describe gear geometry and terminology.
• Analyse spur gear forces and stresses.
• Describe gear train ratios and configurations.
• Design or select a cam profile for a required motion.
• Select couplings and describe misalignment tolerance.
• Describe fasteners, preload, and bolted joint behaviour.
• Describe springs and their selection.

Optional Outcomes

• Describe helical, bevel, and worm gearing.
• Describe belt and chain drives.
• Describe clutches and brakes.
• Describe welded joint design.
• Describe tolerances, fits, and their selection.
• Use design software to verify a hand calculation.

Major Topics

Required Topics

• The design process
• Loads on components
• Combined stresses
• Static failure theories
• Ductile and brittle criteria
• Fatigue and cyclic loading
• S-N curves and endurance limit
• Fatigue modifying factors
• Fatigue factor of safety
• Stress concentrations
• Notch sensitivity
• Selecting a factor of safety
• Material selection
• Shaft design
• Keys, splines, and connections
• Rolling element bearing selection
• Journal bearings and lubrication
• Gear geometry
• Spur gear forces and stresses
• Gear trains
• Cam design
• Couplings and misalignment
• Fasteners and bolted joints
• Springs

Optional Topics

• Helical, bevel, and worm gearing
• Belt and chain drives
• Clutches and brakes
• Welded joint design
• Tolerances and fits
• Design software verification

Resources & Tools

• Your own calculator and a systematic solution format — given, find, assumptions, working, answer with units, sanity check. Adopting one format now is worth more than any single technique in these courses.
• ABET (abet.org) — free accreditation lookup; check which commission accredits your programme before assuming a licensure pathway.
• NCEES (ncees.org) — free information on the FE and PE examinations and state-by-state requirements; the FE reference handbook is free and is a superb formula reference for these courses.
• Florida Board of Professional Engineers (fbpe.org) — free; the authority on Florida licensure.
• Engineering Toolbox and NIST reference data — free property tables and unit conversions; verify anything critical against a primary source.
• Professional societies — ASME, IEEE, ASHRAE, IISE, and ASQ all offer inexpensive student membership, standards access, and local chapter meetings where employers recruit.
• Your programme's laboratory and your instructors — the equipment time is the part you cannot get elsewhere, and it is already paid for.
• Internships and co-op placements — the single strongest predictor of employment at graduation in this field. Start looking a year before you think you should.
• Bearing manufacturers' engineering catalogues (SKF, Timken, and others) — free, and the actual design references practising engineers use for life calculation and mounting practice.
• Machinery's Handbook — the standard reference for this material; your library will have it, and it is worth owning eventually.
• AGMA (agma.org) — the gear standards body; the standards govern real gear design.
• ASME (asme.org) — codes, standards, and inexpensive student membership.

Career Pathways

• Mechanical engineering technologist and technician — SOC 17-3027.
• Electrical and electronic engineering technologist and technician — SOC 17-3023.
• Industrial engineering technologist and technician — SOC 17-3026.
• Manufacturing and production engineering support — process improvement, tooling, and quality.
• Quality engineering and inspection — SOC 51-9061 at technician level, rising into quality engineering.
• Maintenance and reliability engineering — consistently in demand and under-applied for.
• Controls, automation, and systems integration — among the best paid technical work available without a four-year engineering degree.
• Utilities and power — a substantial Florida sector, with generation, transmission, and distribution employment plus storm restoration work.
• Aerospace, defence, and space — Florida's Space Coast is one of the densest concentrations of this work in the country; ⚠ many roles require U.S. citizenship and some a security clearance.
• Theme park and attraction engineering — a genuine and distinctive Florida employer of mechanical, controls, and maintenance engineering talent.
• Building systems, HVAC, and energy management — steady work with a strong Florida market.
• Continue to a bachelor's or a graduate degree — Daytona State's engineering technology bachelor's programmes are the direct route, and see the licensure note about what that degree does and does not qualify you for.
• Machine design and product development — the direct application.
• Reliability and maintenance engineering — where fatigue and bearing knowledge pays daily.
• Applications engineering for component manufacturers — bearings, gearing, drives, and fasteners.

Special Information

⚠⚠ Fatigue is why machines break — and static strength does not predict it

• Most machine components that fail in service fail by fatigue, at stresses well below the yield strength — because the load was applied and removed millions of times.
• ⚠⚠ A component sized on static strength alone is not designed. This is the most consequential idea in the course, and it is the difference between a part that works and one that works for two years and then breaks.
• Fatigue cracks start at stress concentrations — fillets, holes, keyways, threads, and sharp corners. Generous radii are free strength, and a sharp internal corner is a designed-in crack initiation site.
• ⚠ Surface finish matters enormously. Fatigue cracks start at the surface, so a rough finish substantially reduces fatigue strength — and a machining change made for cost can quietly halve a component's life.
• Steel has an endurance limit; many non-ferrous materials do not. Aluminium will eventually fail under repeated loading no matter how low the stress, which changes design philosophy completely.
• ⚠ Fatigue failure gives little warning. The crack grows slowly and invisibly, then the remaining section fails suddenly — which is why inspection intervals exist and why a fatigue-critical part is not run to failure.
• Corrosion and fretting destroy fatigue life, and a component fine in a laboratory can fail early in a salt environment — which is a live concern in coastal Florida.
• Apply the modifying factors honestly. Published endurance limits come from polished laboratory specimens under one loading mode; your part is none of those things.
• Look at broken parts. A fatigue fracture surface has a characteristic appearance, and learning to recognise it makes failure analysis possible.

⚠ A factor of safety is a judgement about consequences, not a number you look up

• The factor of safety accounts for what you do not know — load uncertainty, material variability, analysis approximation, manufacturing variation, and the environment.
• ⚠ A larger factor is not automatically better. It adds weight, cost, and sometimes new failure modes, and in some applications an over-designed part transfers the failure somewhere worse.
• Choose it against the consequence of failure. A part whose failure injures someone justifies a different factor from one that merely stops a machine, and saying which case you are in is part of the design.
• Be honest about your uncertainty. A factor of safety chosen to cover known sloppiness in the analysis is engineering; one chosen to cover unexamined sloppiness is a guess.
• ⚠ Where a code or standard specifies the factor, the code governs. Lifting, pressure, and structural applications have prescribed values that are not open to the designer's preference.
• Document the basis. Somebody will ask why, possibly years later and possibly in a legal context.
• Consider the failure mode as well as the margin — a design that fails gradually and detectably is better than one with a larger margin that fails suddenly.
• Test where you can. Analysis narrows the design; testing is what confirms it, and prototypes exist for that reason.

⚠⚠ An engineering answer is a number, a unit, and a judgement about whether it is plausible

• A number without units is not an answer, and unit errors are the single most common source of catastrophic engineering mistakes — including ones that have destroyed spacecraft.
• Carry units through the calculation rather than adding them at the end. If the units do not come out right, the working is wrong, and this catches errors nothing else will.
• ⚠ Sanity-check every result. Ask whether the magnitude is plausible before writing it down — a beam deflecting three metres or a pump drawing a megawatt is telling you something, and the software will not.
• Estimate first, then calculate. An order-of-magnitude estimate made before the analysis is the cheapest error check available.
• Know your assumptions and state them. Every analysis rests on idealisations — rigid bodies, incompressible flow, linear elasticity — and the failures happen where an assumption stopped being true and nobody noticed.
• Significant figures are a claim about precision. Reporting eight digits from a measurement good to two is a misrepresentation, not thoroughness.
• ⚠ Software output is not verification. Analysis packages return confident, well-formatted answers to badly posed problems — you are responsible for the model, the inputs, and whether the result makes sense.
• Show the working. An answer nobody can check is not usable engineering, and in professional practice it is not acceptable.
• Say when you are unsure. Flagging a doubt is what a competent engineer does; concealing it is how failures propagate.

⚠ Engineering technology and professional engineering licensure in Florida

• Engineering practice is regulated in Florida under Chapter 471, Florida Statutes, through the Board of Professional Engineers and FBPE. Offering engineering services to the public and sealing engineering documents require a professional engineer licence.
• ⚠⚠ Engineering technology and engineering are different educational pathways, and the distinction matters for licensure. Licensure routes are built around programmes accredited by ABET, and ABET accredits engineering and engineering technology under separate commissions with different criteria.
• ⚠ A degree in engineering technology may not qualify a graduate for PE licensure on the same terms as an engineering degree, and in some states not at all. Requirements differ by state and they change.
• If professional licensure is your goal, establish the route before you enrol — ask FBPE directly, ask the programme what its graduates have actually done, and get the answer in writing. This is the same unrecoverable trap this repository records for allied health accreditation, and it is discovered just as late.
• The industry exemption matters in practice. A great deal of engineering work performed inside a manufacturing company does not require a licence, which is why many engineering technology graduates have full technical careers without one.
• Certification is a separate and useful route — NICET, ASQ, and manufacturer certifications are recognised by employers and do not depend on the degree's accreditation category.
• ⚠ Rule 11 applies. Licensure requirements, accreditation criteria, and reciprocity between states all change — verify with FBPE and NCEES rather than relying on this guide.

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 — and it is live in these prefixes, since Daytona State offers both associate-level and bachelor of science in engineering technology coursework in them.

ETM4512 is 3 credits and approximately 45 contact hours, offered spring only at Daytona State.