Maharashtra SSC Workshop Science & Calculation ITI key terms

The smallest measurement a vernier caliper can read, found by dividing the main scale's smallest division by the number of vernier scale divisions. A common value is 0.02 mm.

The smallest length a screw-gauge micrometer can resolve, equal to the pitch of its spindle screw divided by the number of thimble divisions. A typical metric value is 0.01 mm.

A reading shown by an instrument when the true measurement is zero, caused by wear or misalignment. It must be added or subtracted to correct every reading taken.

A ratio expressed as a part per hundred. To convert a fraction to a percentage, multiply by 100; to find a percentage of a quantity, multiply the quantity by the percentage divided by 100.

A comparison of two quantities of the same kind by division, written as a to b or a:b. Both terms must be in the same unit, and the ratio stays the same if both are multiplied or divided equally.

A statement that two ratios are equal, such as a:b = c:d. In a direct proportion, one quantity rises as the other rises; in inverse proportion, one falls as the other rises.

A solving technique in which you first find the value of one unit by division, then multiply by the number of units required. It suits problems on rates, work and cost.

A number written as one whole number over another, showing parts of a whole. The lower number is the denominator and the upper is the numerator; fractions are added only after making denominators equal.

A way of writing fractions using place value after a decimal point, where each place is one tenth of the place to its left. Trailing zeros do not change the value of a decimal.

The surface enclosed by a circle, calculated as pi times the radius squared. Using pi as 3.1416 or 22/7 gives answers accurate enough for most workshop work.

The distance around a circle, equal to pi times the diameter. It is the length of material needed to bend a ring or the distance a wheel travels in one turn.

The space inside a cylinder, found by multiplying the area of its circular base by its height. It is used for tank capacity and for the volume of round bar stock.

For a prism, volume is base area times height. For a pyramid or cone, volume is one third of base area times height, because it tapers to a point.

The part of a cone or pyramid left after the top is cut off parallel to the base. Its volume is found from the two base areas and the height between them.

In a right-angled triangle, the square of the hypotenuse equals the sum of the squares of the other two sides. It is used to find slant heights, diagonals and unknown lengths on jobs.

Ratios linking the angles of a right triangle to its sides: sine is opposite over hypotenuse, cosine is adjacent over hypotenuse, and tangent is opposite over adjacent.

The angle at which a workpiece surface slopes relative to its axis. It is found from the difference in radii divided by the length, using the tangent ratio or a taper formula.

A gradual decrease in diameter along the length of a workpiece, expressed as the difference in diameter per unit length or as a ratio such as 1:20. It is produced by swivelling the compound slide or offsetting the tailstock.

The speed at which the cutting edge of a tool passes over the workpiece surface, usually given in metres per minute. It depends on the material of both tool and workpiece.

The rotational speed of the machine spindle, measured in revolutions per minute. It is calculated from cutting speed and workpiece diameter using the relation speed equals pi times diameter times rpm divided by 1000.

The distance the cutting tool advances per revolution of the workpiece or per stroke, usually in millimetres per revolution. It controls chip thickness and surface finish.

The time a cut takes, calculated as the length of cut divided by the feed rate, or as the number of passes times length divided by feed times spindle speed. Allowances are added for approach and overtravel.

Two ways of stating gear tooth size. Module is pitch circle diameter in millimetres divided by the number of teeth; diametral pitch is the number of teeth per inch of pitch circle diameter.

The diameter of the imaginary circle on which gear teeth roll without slipping. For a spur gear it equals module multiplied by the number of teeth.

The ratio of the number of teeth on the driven gear to the number on the driving gear. It fixes the speed reduction and torque increase between two meshing gears.

The axial distance between corresponding points on adjacent thread crests. For a single-start thread it equals the lead; for a multi-start thread the lead is pitch multiplied by the number of starts.

The distance a screw advances axially in one complete turn. It equals pitch for a single-start thread and pitch times starts for a multi-start thread.

The permitted maximum and minimum sizes of a shaft and hole, and the resulting clearance or interference when they are assembled. Basic size is the nominal size from which deviations are measured.

The total permissible variation in a dimension, equal to the difference between the upper and lower limits. A smaller tolerance means a more precise and usually more costly part.

Clearance exists when the hole is larger than the shaft, allowing movement. Interference exists when the shaft is larger, so the parts must be pressed or shrunk together.

Mass is the quantity of matter in a body, in kilograms. Density is mass per unit volume, so mass equals density times volume, which lets you find the weight of bar stock from its size.

A push or pull that changes or tends to change a body's motion or shape, measured in newtons. One newton accelerates one kilogram at one metre per second squared.

Work is force multiplied by the distance moved along its line of action, in joules. Power is the rate of doing work, in watts, so one watt equals one joule per second.

The turning effect of a force about an axis, equal to force times perpendicular distance from the axis, measured in newton metres. It is the twisting effort delivered by a shaft or spanner.

A device such as a lever, pulley, inclined plane, wedge, screw or wheel and axle that changes the size or direction of an applied force. Mechanical advantage is load divided by effort.

The ratio of useful output to total input, usually expressed as a percentage. It is always less than 100 per cent because friction and other losses remove energy.

Stress is the internal force per unit area in a loaded material, in newtons per square millimetre. Strain is the resulting change in length divided by the original length, and is dimensionless.

The greatest stress a material can take and still return to its original shape when the load is removed. Loading beyond it causes permanent deformation.

Hardness is resistance to scratching or indentation, tested by Brinell or Rockwell methods. Toughness is the ability to absorb energy without fracturing, so a tough part resists shock.

A mixture of two or more metals, or a metal with another element, made to improve properties. Steel is iron with carbon; brass is copper with zinc; bronze is copper with tin.

Controlled heating and cooling of a metal to change its properties. Processes include annealing to soften, hardening by quenching, and tempering to reduce brittleness after hardening.

For a conductor at constant temperature, current equals voltage divided by resistance. It links the three electrical quantities and is written V equals I times R.

The rate at which electrical energy is used, equal to voltage times current in watts. For a resistor it can also be written as current squared times resistance.

In a series circuit the same current flows through every component and resistances add. In a parallel circuit the voltage is common and the total resistance is less than the smallest branch.

Celsius and Fahrenheit are relative scales; Kelvin starts at absolute zero. To convert Celsius to Kelvin add 273, and the boiling point of water is 100 degrees Celsius or 373 kelvin.

Heat is energy transferred because of a temperature difference, measured in joules. Specific heat is the energy needed to raise one kilogram of a substance by one kelvin.

The increase in length of a material when heated, equal to original length times the coefficient of linear expansion times temperature rise. It explains why fits and clearances change when parts get hot.

Gear worn to protect against workplace hazards: safety goggles for eye protection, gloves against cuts and chemicals, safety shoes against falling objects, and ear protection against noise.

Fixed or interlocked barriers that keep hands and clothing away from rotating parts such as gears, belts and chucks. Guards must never be removed while a machine is running.

A procedure in which the power source of a machine is switched off, locked and tagged before maintenance, so it cannot be started accidentally while someone is working on it.

Preventing and fighting fire by keeping flammable materials away from heat sources and choosing the right extinguisher. Classes are A for solids, B for liquids, C for gases and D for metals.

A property by which certain materials attract iron and exert forces on moving charges. Like poles repel and unlike poles attract, and a magnetic field is strongest at the poles.