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NSSCO Metalwork and Welding 6188 study materials
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NSSCO Metalwork and Welding 6188 practice questions

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Question 1Workshop safety, health and environment

A learner is about to use a pedestal grinder to sharpen a chisel. Which item of personal protective equipment is specifically required to protect the eyes from flying metal particles?

  1. A dust mask
  2. Tinted sunglasses
  3. Impact-rated safety goggles Correct answer.
  4. A welding helmet with a dark filter lens

Explanation

Grinding throws small metal particles at high speed, so eye protection must resist impact. Safety goggles with impact-rated lenses seal around the eyes and are the correct choice. A welding helmet is for arc radiation, sunglasses are not impact-rated, and a dust mask protects the respiratory tract, not the eyes.

Question 2Workshop safety, health and environment

Which type of fire extinguisher is suitable for a small fire involving electrical welding equipment that is still energised?

  1. Water stored-pressure extinguisher
  2. Foam extinguisher
  3. Carbon dioxide (CO2) extinguisher Correct answer.
  4. Wet chemical extinguisher

Explanation

Electrical fires need a non-conducting extinguishing agent. Carbon dioxide does not conduct electricity and leaves no residue, so it is suitable for energised equipment. Water, foam and wet chemical extinguishers conduct electricity and can cause electric shock.

Question 3Workshop safety, health and environment

When moving an acetylene cylinder a short distance across the workshop, what is the correct practice?

  1. Roll it on its side while gripping the valve spindle
  2. Lift it by the valve guard with a helper
  3. Drag it by the regulator hose to save time
  4. Use a cylinder trolley with the valve closed Correct answer.

Explanation

Compressed gas cylinders must be moved with a proper trolley, kept upright and with the valve closed and valve protection fitted. Lifting by the valve or rolling the cylinder risks damaging the valve and releasing gas. Dragging by the hose can tear the hose and whip the cylinder.

Question 4Workshop safety, health and environment

A welder is making a long run of fillet welds on galvanised steel inside a workshop bay. What is the most appropriate control for the metal fume produced?

  1. Use local exhaust ventilation positioned close to the arc Correct answer.
  2. Wear a dust mask and rely on general dilution
  3. Open a nearby window and continue welding without extra equipment
  4. Weld faster to reduce the time fumes are produced

Explanation

Welding galvanised steel produces zinc oxide fume that can cause metal fume fever. Local exhaust ventilation captures fume at the source before it reaches the breathing zone. General ventilation and a dust mask are less reliable, and welding faster does not remove the hazard.

Question 5Workshop safety, health and environment

On a bench or pedestal grinder, the gap between the tool rest and the wheel should be adjusted to what maximum, and why?

  1. 10 mm or more, so that the wheel runs cooler during use
  2. No gap is needed provided the wheel guard is fitted
  3. 25 mm, so that large chisels and punches fit easily
  4. 3 mm or less, to stop the workpiece being pulled in Correct answer.

Explanation

The tool rest must be set close to the wheel, commonly 3 mm or less, so that the workpiece cannot be wedged between the rest and the wheel and dragged in. A large gap increases the risk of the work being pulled from the operator's hands. The guard alone does not remove this trapping risk.

Question 6Workshop safety, health and environment

Before starting oxy-acetylene cutting in a workshop area where there are combustible materials nearby, which precaution is most appropriate?

  1. Open both gas cylinder valves fully to make the cutting faster
  2. Remove or shield combustibles and keep fire-fighting equipment ready Correct answer.
  3. Spray water on nearby combustibles once the cutting has begun
  4. Cut quickly and check the area only at the very end of the working shift

Explanation

Hot work should only start after combustible materials have been removed or covered with fire-resisting protection. Suitable extinguishing equipment and a fire watch are needed because sparks can travel and smoulder. Wetting after work starts is too late, and end-of-shift checks alone do not control ignition.

Question 7Workshop safety, health and environment

A welding machine has a damaged mains cable with exposed inner conductors. What is the correct action?

  1. Continue only if the machine stands on a dry concrete floor
  2. Isolate it, tag it out of service and report the defect Correct answer.
  3. Stand on a rubber mat and use a lower welding current
  4. Wrap the damaged section with insulating tape and keep working

Explanation

A damaged cable with exposed conductors is a shock and fire hazard. The machine must be isolated from the supply, labelled as defective and repaired by a competent person before use. Tape, dry floors and rubber mats do not make the cable safe.

Question 8Workshop safety, health and environment

Why are flashback arrestors fitted to oxy-acetylene hoses or regulators?

  1. To prevent the gas cylinder from moving during cutting work
  2. To stop flame travelling back up the hose to the cylinder Correct answer.
  3. To reduce the gas pressure before it reaches the cutting torch
  4. To filter solid impurities out of the acetylene gas supply

Explanation

A flashback is a flame that travels back through the torch and hose. Flashback arrestors contain a non-return valve and flame trap that stop the flame reaching the cylinder, where it could cause an explosion. They do not filter gas, regulate pressure or secure the cylinder.

Question 9Workshop safety, health and environment

An oxygen regulator shows signs of oil contamination at the outlet. Why is this a serious hazard, and what should be done?

  1. Oil can ignite explosively with oxygen; isolate the regulator Correct answer.
  2. Oil makes the regulator sticky; apply graphite grease to free the valve
  3. Oil only causes a bad smell; wipe the outlet with a rag and continue
  4. Oil lowers the oxygen purity; drain the cylinder and refit the regulator

Explanation

Oxygen supports combustion and, under pressure, oil or grease can ignite and burn violently or explode. Equipment used with oxygen must be free of oil and grease. The regulator should be isolated, tagged and dealt with by a competent person, not cleaned casually or greased.

Question 10Workshop safety, health and environment

A welder must work inside a large metal tank. Which combination of controls is essential before entry?

  1. Gas test, ventilate, use a standby person and rescue plan Correct answer.
  2. Working in short bursts and keeping the welding torch lit
  3. Opening the tank hatch and wearing a disposable dust mask
  4. A welding helmet, leather gloves and a leather apron only

Explanation

A tank is a confined space where toxic fumes, displacement of oxygen and heat build-up can occur. Entry requires atmospheric testing, forced ventilation, a competent standby person outside and a rescue plan. PPE alone, an open hatch or short bursts do not control the confined-space hazards.

Question 11Workshop safety, health and environment

A welder has finished a fillet weld and is about to remove the slag with a chipping hammer. Which eye protection is appropriate for this task?

  1. Clear safety goggles Correct answer.
  2. No eye protection is needed for cold slag
  3. A dark arc-welding helmet with a shade 11 filter lens
  4. Tinted sunglasses for indoor use

Explanation

Chipping slag produces hard fragments that can fly into the eyes at speed, so impact-rated safety goggles or a face shield are needed. A dark welding lens is intended to filter arc radiation, not to give clear vision for chipping, and sunglasses provide no impact protection.

Question 12Workshop safety, health and environment

In the workshop gas store, how should full oxygen cylinders be kept?

  1. Upright with the valves open so pressure can be read
  2. Lying horizontally on the floor to save height
  3. Upright and secured, with valve protection caps fitted Correct answer.
  4. Beside oily rags, so they are easy to find

Explanation

Full cylinders are stored upright and restrained so that they cannot fall, and valve protection caps shield the outlet from damage. Valves should remain closed in storage, and oxygen must be kept away from oil or grease because contact can cause a fire.

Question 13Workshop safety, health and environment

A cold chisel used at the bench has developed a mushroom-shaped head. What is the correct action?

  1. Wrap the head in cloth before striking
  2. Dress the head back to shape Correct answer.
  3. Heat the head and bend the mushroom flat
  4. Continue using it, but strike the head more gently

Explanation

A mushroomed head can break off and send sharp metal fragments into the eyes or hands. The head should be ground or dressed back to the correct chamfer, or the chisel should be replaced.

Question 14Workshop safety, health and environment

A welder increases the welding current from about 80 A to about 200 A on the same manual metal arc set. What should be done to the helmet filter lens?

  1. Remove the filter and rely on the clear cover lens
  2. Keep the same shade number, because arc brightness does not change
  3. Use a lower shade number to see the arc more clearly
  4. Use a higher shade number to give more protection Correct answer.

Explanation

A higher current produces a more intense arc with more ultraviolet and visible radiation, so a higher shade number is needed. The filter shade must suit the welding process and current, not just personal preference.

Question 15Workshop safety, health and environment

Where should the welding return clamp be fixed when welding a steel fabrication on a bench?

  1. To the electrode holder cable
  2. To the gas cylinder beside the bench
  3. To the metal bench, well away from the weld
  4. On clean metal near the weld Correct answer.

Explanation

The return clamp should make a direct, low-resistance path from the workpiece back to the welding machine. Placing it on clean metal close to the weld stops current from travelling through bearings, chains or bench surfaces.

Question 16Workshop safety, health and environment

After oxy-acetylene cutting has finished in a workshop bay, why should a fire watch be kept for a period?

  1. To make sure the metal has cooled enough to measure
  2. To allow the cutting torch to cool before it is put away
  3. To detect smouldering slag that could start a fire later Correct answer.
  4. To check that gas cylinders have not lost pressure

Explanation

Cutting throws sparks and hot slag that can lodge in cracks, waste or clothing and smoulder for a long time. A fire watch checks for smoke or heat after the hot work stops, when a fire may still develop.

Question 17Workshop safety, health and environment

A learner spends most of a morning using a pedestal grinder. Hearing protection is required mainly to prevent which health effect?

  1. Metal fume fever caused by inhaling zinc oxide
  2. Vibration white finger caused by holding the workpiece
  3. Permanent hearing loss caused by prolonged high noise Correct answer.
  4. Arc eye caused by ultraviolet radiation

Explanation

Grinding produces high sound levels that can damage the inner ear over time, and the loss is permanent. Hearing protection reduces the noise reaching the ear; it does not prevent vibration, arc radiation or fume exposure.

Question 18Workshop safety, health and environment

Why is it unsafe to use the workshop compressed-air line to blow metal dust off clothing or bare skin?

  1. The air line is only intended for inflating tyres
  2. The jet can drive particles into eyes or skin Correct answer.
  3. The air is too cold and may chill the skin
  4. Compressed air removes the oil needed on machine slides

Explanation

A compressed-air jet can penetrate skin or drive metal particles into the eyes, causing injury or air embolism. Clothing should be cleaned with a brush or vacuum, not with the air line.

Question 19Workshop safety, health and environment

Manual metal arc welding produces fume that drifts through the welder's breathing zone even though the bay has roof ventilation. Which control is most appropriate?

  1. Open the workshop doors wider
  2. Increase the general roof ventilation rate
  3. Fit local exhaust ventilation close to the arc Correct answer.
  4. Wear a dust mask and continue welding

Explanation

General ventilation dilutes fume in the whole building but does not stop it entering the breathing zone. Local exhaust ventilation captures fume at the arc before it spreads, so it is the more effective engineering control.

Question 20Workshop safety, health and environment

A workpiece jams in a pedestal drill. Before the learner reaches in to free it, what is the correct isolation step?

  1. Press the emergency stop button and leave it at that
  2. Ask another learner to hold the start switch in the off position
  3. Pull the plug out and leave it on the bench beside the drill
  4. Lock off the isolator and wait for the spindle to stop Correct answer.

Explanation

Lock-off isolation prevents another person from restarting the drill while the learner's hands are near the spindle. Waiting for the spindle to stop is part of the same safe procedure; an emergency stop alone may be reset easily.

Question 21Metal materials and properties

Which of the following materials used in a metalwork workshop is classified as a ferrous metal?

  1. Mild steel Correct answer.
  2. Copper
  3. Aluminium
  4. Brass

Explanation

Ferrous metals are those whose main constituent is iron. Mild steel is an alloy of iron and a small amount of carbon, so it is ferrous. Aluminium, copper and brass are non-ferrous because they contain no iron as their base metal.

Question 22Metal materials and properties

Which mechanical property allows a metal to be drawn out into a thin wire without fracturing?

  1. Ductility Correct answer.
  2. Brittleness
  3. Elasticity
  4. Malleability

Explanation

Ductility is the ability of a metal to be stretched or drawn into wire without breaking, as in wire drawing. Malleability allows shaping by hammering into sheets, while brittleness means fracture with little deformation. Elasticity is the ability to return to the original shape after loading.

Question 23Metal materials and properties

In plain carbon steel, increasing the carbon content within the normal range has which main effect?

  1. It lowers the melting point and makes the steel softer
  2. It increases electrical conductivity
  3. It makes the steel non-magnetic
  4. It increases hardness and tensile strength Correct answer.

Explanation

Carbon is the main alloying element in plain carbon steel. Raising the carbon content increases hardness and tensile strength, although it reduces ductility and weldability. This effect is used when selecting steels for cutting tools rather than for structural work.

Question 24Metal materials and properties

A cold chisel must keep a sharp cutting edge while being struck. Which material is most suitable?

  1. Mild steel
  2. Wrought iron
  3. Cast iron
  4. High carbon steel Correct answer.

Explanation

A cold chisel needs a hard, wear-resistant edge, so a high carbon steel of about 0.8–1.0% carbon is chosen and then hardened and tempered. Mild steel and wrought iron are too soft to hold an edge, and cast iron is too brittle for impact.

Question 25Metal materials and properties

Which heat treatment involves heating steel above its critical temperature and then cooling it very slowly in the furnace to give maximum softening?

  1. Normalising
  2. Hardening
  3. Tempering
  4. Annealing Correct answer.

Explanation

Annealing is a softening treatment: the steel is heated above its critical temperature and then cooled very slowly, usually in the furnace. This relieves internal stresses and refines the grain structure. Normalising cools in air and is not intended to give maximum softening.

Question 26Metal materials and properties

When the zinc coating on a galvanised steel water tank is scratched, the exposed steel is still protected from rusting mainly because:

  1. Zinc seals the scratch with a hard oxide
  2. Zinc corrodes in preference to iron Correct answer.
  3. Zinc lowers the carbon content of the steel
  4. Zinc makes the steel cathodic to the soil

Explanation

Zinc is higher than iron in the reactivity series, so it corrodes preferentially and protects the exposed steel sacrificially. This is why galvanised components remain protected even when the coating is scratched. The zinc oxide barrier alone would be broken at a scratch.

Question 27Metal materials and properties

The corrosion resistance of stainless steel is mainly due to the presence of which alloying element?

  1. Carbon
  2. Chromium Correct answer.
  3. Nickel
  4. Manganese

Explanation

Stainless steel contains at least about 10.5% chromium. The chromium reacts with oxygen to form a thin, adherent chromium oxide layer that protects the surface from further corrosion. If the layer is damaged it re-forms in air.

Question 28Metal materials and properties

Which pair of metals is alloyed to produce brass?

  1. Copper and tin
  2. Copper and aluminium
  3. Copper and nickel
  4. Copper and zinc Correct answer.

Explanation

Brass is an alloy of copper and zinc, with zinc usually between about 5% and 45%. Bronze is copper alloyed with tin, and cupronickel is copper with nickel. These are all non-ferrous alloys.

Question 29Metal materials and properties

A low carbon steel lever is to be given a hard, wear-resistant surface while its core remains tough. Which process is most suitable?

  1. Normalising
  2. Through hardening and tempering
  3. Case hardening (carburising) Correct answer.
  4. Annealing

Explanation

Case hardening, such as carburising, adds carbon to the surface of a low carbon steel and then quenches it, producing a hard case. The low carbon core stays tough and absorbs shock. Through hardening would make the whole section hard and less tough.

Question 30Metal materials and properties

A steel shaft fails after many cycles of reversing load, although it never exceeded the yield strength. Which material property was most inadequate?

  1. Malleability
  2. Fatigue resistance Correct answer.
  3. Hardness
  4. Creep resistance

Explanation

Fatigue resistance is the ability to withstand many cycles of fluctuating stress without cracking. Fatigue failure can occur at stresses well below the yield strength, so a shaft may fail even though it never yielded. Creep resistance concerns slow deformation at high temperature.

Question 31Metal materials and properties

A bench vice body in a metalwork workshop is commonly made from grey cast iron. Which property makes grey cast iron suitable for this use?

  1. It is highly ductile and can be forged into thin sections.
  2. It can be quenched to give a very hard, tough surface.
  3. It has high electrical conductivity and a low melting point.
  4. It has good compressive strength and damps vibration. Correct answer.

Explanation

Grey cast iron contains graphite flakes, which give it good compressive strength and useful vibration damping, making it suitable for heavy, rigid workshop equipment such as a vice body. It is brittle in tension and is not normally selected for high ductility or forging.

Question 32Metal materials and properties

In the traditional alloy bronze, copper is alloyed mainly with which metal?

  1. Lead
  2. Tin Correct answer.
  3. Zinc
  4. Nickel

Explanation

Bronze is traditionally an alloy of copper and tin. Zinc is the main alloying element in brass, while lead and nickel may be added to special copper alloys but are not the traditional main addition to bronze.

Question 33Metal materials and properties

Aluminium develops a thin oxide film on its surface. Why does this film help aluminium resist further corrosion outdoors?

  1. The oxide film makes the metal strongly magnetic.
  2. The oxide film makes the metal more brittle.
  3. An adherent oxide layer protects the metal beneath. Correct answer.
  4. The oxide film lowers the melting point of aluminium.

Explanation

The oxide layer that forms on aluminium is adherent and relatively stable, so it seals the surface and limits further attack by air and moisture. This is why aluminium can be used outdoors without a painted coating in many situations.

Question 34Metal materials and properties

A medium carbon steel component has been hardened by quenching. It is then reheated to a lower temperature and cooled. What is the main purpose of this second treatment?

  1. To relieve stresses and improve toughness Correct answer.
  2. To convert the steel into cast iron
  3. To make the steel permanently magnetic
  4. To increase the carbon content throughout the steel

Explanation

The second treatment is tempering. Reheating a hardened steel below its critical temperature relieves internal stresses from quenching and reduces brittleness, giving a better balance of hardness and toughness.

Question 35Metal materials and properties

A lathe tool is used to cut steel at high speed and the cutting edge becomes red hot. Which property is most important for the tool material?

  1. Hot hardness Correct answer.
  2. Low density
  3. High malleability
  4. High electrical conductivity

Explanation

A cutting tool that becomes hot must retain its hardness at elevated temperature, a property often called hot hardness or red hardness. If the tool softens when hot, the cutting edge will wear rapidly or deform.

Question 36Metal materials and properties

Which test is used to assess a metal's resistance to failure under a sudden shock load?

  1. Brinell hardness test
  2. Bend test
  3. Tensile test
  4. Izod impact test Correct answer.

Explanation

The Izod impact test measures the energy absorbed by a notched specimen when struck by a swinging hammer, so it indicates resistance to sudden shock loading. Toughness is the property being assessed.

Question 37Metal materials and properties

A copper strip is chosen for an earthing connection in a welding workshop. Which property of copper is most important for this application?

  1. High brittleness
  2. Low melting point
  3. High hardness
  4. High electrical conductivity Correct answer.

Explanation

An earthing connection must carry fault current safely to earth, so low electrical resistance is essential. Copper is widely used because it has very high electrical conductivity and can be formed into flexible strips.

Question 38Metal materials and properties

Why is low carbon steel generally easier to weld than high carbon steel?

  1. It contains more chromium, which prevents oxidation during welding.
  2. It melts at a much lower temperature than every other steel.
  3. It has no grain structure to distort during heating.
  4. Its lower carbon content reduces hard, brittle zones. Correct answer.

Explanation

Carbon increases the hardenability of steel, so high carbon steel is more likely to form hard, brittle martensite in the heat-affected zone when it cools quickly after welding. Low carbon steel is less prone to this problem and generally has better weldability.

Question 39Metal materials and properties

A stainless steel fitting for a marine application is specified as grade 316 rather than grade 304. Which alloying element in 316 improves its resistance to pitting corrosion by chlorides?

  1. Phosphorus
  2. Molybdenum Correct answer.
  3. Sulphur
  4. Copper

Explanation

Grade 316 stainless steel contains molybdenum, typically around 2 to 3 percent, which improves resistance to pitting and crevice corrosion in chloride-containing environments such as seawater. Chromium provides the passive film, but molybdenum strengthens protection against localised attack.

Question 40Metal materials and properties

Plain carbon steel containing about 0.8% carbon is heated above its critical temperature and then cooled slowly. Which microstructure is produced?

  1. Martensite
  2. Ferrite with free cementite
  3. Austenite
  4. Pearlite Correct answer.

Explanation

About 0.8% carbon is the eutectoid composition of plain carbon steel. When this steel is cooled slowly from the austenite region, the austenite transforms into pearlite, which consists of alternating layers of ferrite and cementite.

Question 41Measuring, marking out and inspection

A fitter must scribe a line exactly 12 mm from a straight machined edge on a small steel plate clamped in a bench vice. Which tool is designed for this setting-out task?

  1. Spring dividers
  2. Odd-leg caliper Correct answer.
  3. Trammel
  4. Centre punch

Explanation

An odd-leg caliper (jenny caliper) has one bent leg that registers against the edge of the workpiece while the straight scribing leg is set to the required distance from a steel rule. Because the bent leg follows the edge, a line parallel to that edge can be scribed in one continuous stroke. Spring dividers and trammels are set from a centre point and are used for circles and arcs, not edge-parallel lines.

Question 42Measuring, marking out and inspection

Which part of a standard vernier caliper is used to measure the internal diameter of a bore?

  1. The depth rod
  2. The lower jaws
  3. The vernier scale
  4. The upper jaws Correct answer.

Explanation

The upper jaws are the small knife-edged jaws on top of the caliper head; they are inserted into a bore and opened until they touch the walls, and the reading is then taken from the scales. The lower jaws are for external measurements and the depth rod measures depths. The vernier scale is a reading device, not a measuring contact surface.

Question 43Measuring, marking out and inspection

Which point angle should be ground on a centre punch used to mark the position of a hole before drilling?

  1. 30°
  2. 45°
  3. 90° Correct answer.
  4. 60°

Explanation

A centre punch is ground to a 90° included angle so that a hammer blow produces a wide, deep cone that guides the drill point and resists wander. A dot punch, used for lighter layout marks, is ground to 60°. A sharper angle such as 30° or 45° would give a narrow, shallow mark that the drill could easily push off centre.

Question 44Measuring, marking out and inspection

A metric outside micrometer shows the barrel sleeve reading 7.5 mm exposed and the thimble line coinciding with the 28th division. What is the micrometer reading?

  1. 7.50 mm
  2. 7.28 mm
  3. 7.58 mm
  4. 7.78 mm Correct answer.

Explanation

The thimble has 50 divisions, so each division represents 0.01 mm; 28 divisions therefore add 0.28 mm. Adding this to the 7.5 mm exposed on the barrel sleeve gives 7.78 mm. The half-millimetre mark on the sleeve must be counted before the thimble value is added.

Question 45Measuring, marking out and inspection

A vernier caliper with a least count of 0.02 mm shows a main-scale reading of 24 mm, and the 13th vernier division lines up exactly with a main-scale mark. What is the measured size?

  1. 24.13 mm
  2. 24.65 mm
  3. 25.26 mm
  4. 24.26 mm Correct answer.

Explanation

With a least count of 0.02 mm, the vernier contribution is found by multiplying the coinciding division number by 0.02 mm, giving 13 × 0.02 = 0.26 mm. Adding this to the 24 mm main-scale value gives 24.26 mm. Reading the vernier correctly depends on identifying the single line that aligns best, not the first line that appears close.

Question 46Measuring, marking out and inspection

Why is marking-out fluid (layout dye) applied to a metal surface before scribing?

  1. To lubricate the scriber so it glides across the plate
  2. To provide a contrasting background that makes fine scribed lines visible Correct answer.
  3. To harden the surface so scribed lines are not rubbed away
  4. To clean the surface before marking out

Explanation

A thin coat of marking-out fluid dries to a coloured film that contrasts with the bright metal exposed by the scriber, so fine lines stand out clearly. This improves accuracy when following a line during cutting or drilling, and a scribed line is far easier to see than a scratch on bare metal. The fluid has no hardening or lubricating function, and surfaces must already be cleaned and degreased before it is applied.

Question 47Measuring, marking out and inspection

A 20 mm bore is checked with a plug gap gauge. The 'go' end enters the bore and the 'no-go' end also enters fully. What does this result indicate?

  1. The gauge has been used upside down
  2. The bore is oversize, so the part should be rejected Correct answer.
  3. The bore is within the permitted limits
  4. The bore is undersize and must be reamed

Explanation

A limit plug gauge is made so that the 'go' end must enter a conforming bore while the 'no-go' end must not. If the 'no-go' end also enters, the bore is larger than the upper limit and the part is oversize. Such a bore cannot be corrected by further machining, which is why limit gauging is done before additional work.

Question 48Measuring, marking out and inspection

A feeler gauge is the appropriate instrument for which of the following inspection tasks?

  1. Measuring shaft diameter
  2. Checking valve tappet clearance Correct answer.
  3. Checking a chamfer angle
  4. Measuring drilled hole depth

Explanation

A feeler gauge is a set of thin, accurately ground steel leaves of known thickness used to check narrow gaps. The correct leaf is the thickest one that will slide into the gap with slight drag, which gives the clearance directly. Diameters are measured with calipers or micrometers, depths with a depth gauge, and angles with a protractor.

Question 49Measuring, marking out and inspection

A fitter suspects that an engineer's square is out of true. He scribes a line along the blade against a straight edge, turns the square over and scribes a second line from the same edge, and finds the two lines coincide exactly. What is the correct conclusion?

  1. The blade is not hardened, so the test proves nothing
  2. The straight edge is worn, so the test cannot be trusted
  3. The square is true, because any error would be doubled and appear as two separate lines Correct answer.
  4. The square is out of true by the gap between the lines

Explanation

This is the reversal test for a square: turning the stock over onto the same straight edge reverses any error in the blade angle, so a faulty square produces two lines that diverge by twice the error. Coinciding lines therefore show that the blade is square to the stock within the accuracy of scribing. The test works on any straight edge that is itself straight, and hardening of the blade does not affect the geometry being checked.

Question 50Measuring, marking out and inspection

An outside micrometer reads 0.03 mm when its measuring faces are closed clean. It is then used to measure a shaft and the reading is 12.46 mm. What is the actual diameter of the shaft?

  1. 12.49 mm
  2. 12.43 mm Correct answer.
  3. 12.40 mm
  4. 12.76 mm

Explanation

A reading of 0.03 mm with the faces closed is a positive zero error, meaning the instrument adds 0.03 mm to every measurement. The error must therefore be subtracted, giving 12.46 − 0.03 = 12.43 mm. Zero error is checked before use and the instrument should be cleaned and, if possible, adjusted or replaced before accurate work continues.