Tawjihi Vocational Engineering flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

First-angle projection layout

The object is placed between the observer and the projection plane. The view from above is drawn below the front view, and the view from the left is drawn on the right.

Vernier calliper least count

Least count equals one main-scale division minus one vernier-scale division. With 1 mm main divisions and 50 vernier divisions spanning 49 mm, the least count is 0.02 mm.

Micrometer least count

Least count equals screw pitch divided by the number of thimble divisions. A 0.5 mm pitch with 50 thimble divisions gives a least count of 0.01 mm.

Ohm's law and power

Voltage equals current times resistance, V = I × R. Power equals voltage times current, P = V × I, which also equals I²R and V²/R.

Parallel resistance formula

The reciprocal of total resistance equals the sum of the reciprocals of the individual resistances. Voltage is the same across every branch, and current divides inversely with resistance.

Series RLC resonance

At resonance the inductive and capacitive reactances are equal, so impedance is minimum and equals the resistance. The resonant frequency is f = 1/(2π√(LC)).

Turning cutting speed

Cutting speed in metres per minute equals π times workpiece diameter in millimetres times spindle speed in revolutions per minute, divided by 1000.

Fillet weld throat thickness

The throat thickness of a fillet weld equals 0.707 times the leg length. The throat is the shortest distance from the weld root to the weld face.

Up versus down milling

In up milling the cutter rotates against the feed and chips start thin. In down milling the cutter rotates with the feed, chips start thick, and finish is better on rigid machines.

Quenching and tempering

Quenching rapidly cools heated steel to form hard, brittle martensite. Tempering reheats it to a lower temperature to reduce brittleness and relieve internal stress while keeping toughness.

Brinell versus Rockwell hardness

The Brinell test presses a 10 mm ball into the surface and suits soft to medium metals. Rockwell C uses a diamond cone and suits hardened steel.

Brass versus bronze

Brass is a copper–zinc alloy. Bronze is mainly copper with tin, or aluminium in aluminium bronze. Bronze generally has better wear resistance and corrosion resistance.

Moment of a force

The moment about a point equals force times the perpendicular distance from the point to the line of action. Its unit is the newton metre.

Limiting friction

Limiting friction equals the coefficient of friction multiplied by the normal reaction, F = μN. Motion begins when the applied force just exceeds this value.

Simply supported beam central load

For a central point load W on a span L, each reaction is W/2 and the maximum bending moment is WL/4 at mid-span.

Bending stress formula

Bending stress equals bending moment times distance from the neutral axis divided by the second moment of area, σ = My/I. Maximum stress occurs at the greatest distance y.

Lockout/tagout procedure

Isolate all hazardous energy, apply a personal lock and tag by each worker, verify isolation by trying to start, then maintain the lock until the worker removes it personally.

Hierarchy of controls

From most to least effective: elimination, substitution, engineering controls, administrative controls, then personal protective equipment. PPE is the last line of defence.

Fire classes and extinguishers

Class A solid combustibles, B flammable liquids, C gases, D metals, F cooking oils. Water must not be used on flammable liquid, gas, metal, or live electrical fires.

Preventive versus predictive maintenance

Preventive maintenance is scheduled by time or usage. Predictive maintenance acts on measured condition such as vibration, temperature, or oil analysis before failure occurs.

Misalignment vibration signature

Angular misalignment produces strong vibration at one and two times running speed. Parallel misalignment produces mainly two times running speed in the radial direction.

Bearing over-greasing

Excess grease raises bearing temperature and can cause failure. The correct fill is about one-third to one-half of the free space inside the bearing housing.

Troubleshooting sequence

Observe symptoms, gather data, form a hypothesis, test it, correct the fault, then verify the repair and record the result for future reference.

Process capability Cpk

Cpk equals the smaller of (upper limit minus mean) or (mean minus lower limit), divided by three sigma. It measures capability while accounting for process centring.

Go/no-go gauge function

A go/no-go gauge checks whether a feature lies within limits without giving a size value. The go end must pass and the no-go end must not.

Stress and strain

Stress equals force divided by cross-sectional area, in newtons per square millimetre or megapascals. Strain equals change in length divided by original length and is dimensionless.

Unit conversion factors

One inch equals 25.4 mm. One kilogram-force equals 9.81 N. One bar equals 100 kPa. One kilowatt equals 1.36 horsepower. One kilowatt-hour equals 3.6 megajoules.

Gear ratio

Gear ratio equals teeth on the driven gear divided by teeth on the driving gear, which also equals driver speed divided by driven speed. A larger ratio reduces output speed and increases torque.

Break-even quantity

Break-even quantity equals fixed costs divided by the difference between selling price per unit and variable cost per unit. At this quantity total revenue equals total cost.

Net present value decision rule

Discount each future cash flow by (1 + r) raised to its period, sum them, and subtract the initial investment. Accept the project when the result is positive.

Critical path and float

The critical path is the longest path through the activity network and sets the shortest project duration. Activities on it have zero float; delaying any one delays the project.

Work order contents

A work order records the job description, location, requested date, assigned technician, parts used, labour hours, and sign-off. It is the formal record of maintenance work performed.