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ITI/NCVT Mechanic Machine Tool Maintenance (AITT Theory) study materials
ITI/NCVT Mechanic Machine Tool Maintenance (AITT Theory) study resources

ITI/NCVT Mechanic Machine Tool Maintenance (AITT Theory) practice questions

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Question 1Occupational safety, health and environment in machine shops

A mechanic is sharpening a high-speed steel drill on a bench grinder. Which eye protection is the correct minimum for this job?

  1. A cloth cap pulled down over the forehead
  2. Tinted sunglasses
  3. Impact-rated safety goggles with side shields Correct answer.
  4. Ordinary prescription spectacles with plain lenses

Explanation

The grinding wheel throws abrasive grains and hot HSS fragments at high velocity from the wheel face, and particles travel sideways as well as forward. Only impact-rated goggles with side protection seal the eye from both directions, so they are the minimum for anyone at the grinder.

Question 2Occupational safety, health and environment in machine shops

A small fire starts inside an energised electrical control panel of a milling machine. Which extinguisher is suitable for the first attack?

  1. Carbon dioxide (Class C) extinguisher Correct answer.
  2. Foam (Class A/B) extinguisher
  3. Wet chemical (Class F) extinguisher
  4. Water-type (Class A) extinguisher

Explanation

Live electrical equipment needs a non-conductive medium, and CO2 also leaves no residue to damage terminals and circuit boards. Water, foam and wet chemical agents conduct electricity and create an electrocution risk to the person holding the nozzle.

Question 3Occupational safety, health and environment in machine shops

A hose on the coolant system bursts and water-mixed coolant spreads across the walkway beside a lathe. What is the immediate correct action?

  1. Barricade the area, clean up at once and trace the leak source Correct answer.
  2. Leave it for the end-of-shift cleaning gang to handle
  3. Wash it into the nearest floor drain with a bucket of water
  4. Spread dry machining chips over the puddle so the oil soaks away

Explanation

Water-mixed coolant makes a concrete floor extremely slippery, so the spill must be isolated, cleaned promptly and the source found and repaired to stop it recurring. Draining it away or hiding it under chips only moves the slip hazard or creates an environmental problem.

Question 4Occupational safety, health and environment in machine shops

On a horizontal milling machine, when must the cutter guard be in position?

  1. Only during the final finishing pass
  2. Only when the job is longer than 300 mm
  3. At all times while the cutter is revolving Correct answer.
  4. Only when a trainee is operating the machine

Explanation

Contact with a rotating cutter happens just as easily during setting, gauging or cleaning as during the cutting pass, so the guard stays on whenever the spindle turns. It may be removed only after the spindle has come to rest.

Question 5Occupational safety, health and environment in machine shops

A mechanic must change the drive belt of a lathe fed from a wall-mounted isolator. What has to be done before the belt guard is opened?

  1. Select the lowest spindle speed and work with the guard held open
  2. Press the emergency stop on the control panel and start work at once
  3. Isolate, lock and tag the supply, then prove the machine is dead Correct answer.
  4. Ask the operator to stand by the isolator until the job is finished

Explanation

The emergency stop drops control power only and can be reset by anyone, so it cannot protect a person working inside the belt drive. Energy must be isolated at the source, locked and tagged by the person doing the work, and the dead condition verified before the guard comes off.

Question 6Occupational safety, health and environment in machine shops

An operator develops redness, dryness and cracking between the fingers after several weeks on a machine using water-mixed cutting fluid. What is the most appropriate action?

  1. Wash the hands several times a shift with solvent to strip the oil away
  2. Wear one pair of gloves for the whole shift without rinsing them out
  3. Wait for the annual medical examination before reporting the condition
  4. Check coolant concentration and pH, provide gloves and barrier cream, and refer the case Correct answer.

Explanation

Coolant dermatitis comes from skin defatting, from bacterial growth when the mix is too weak, and from irritant trapped inside gloves. Concentration, pH and sump cleanliness must be controlled, gloves and barrier cream provided, and the case referred early so it does not become chronic.

Question 7Occupational safety, health and environment in machine shops

A heavy machine vice has to be moved from the floor onto the bench. Which technique is correct?

  1. Straight legs and a bent back, with the load held away from the body
  2. A jerking lift to get the weight moving in the first instant
  3. A quick twisting swing of the trunk to place the load on the bench
  4. Bent knees, load held close, and a helper for a heavy vice Correct answer.

Explanation

Bending the knees keeps the load within the strong leg muscles, and holding it close shortens the moment arm on the lumbar spine. A heavy vice should be a two-person lift or a trolley job; twisting or jerking under load is a common cause of disc injury.

Question 8Occupational safety, health and environment in machine shops

Why must compressed air never be used to blow chips off a lathe bed or off clothing?

  1. Chips can be blown into the eyes or injected under the skin Correct answer.
  2. It lowers the line pressure available for pneumatic clamping
  3. It causes rapid cooling and thermal cracking of the slideways
  4. It raises the mixed coolant concentration above the recommended value

Explanation

An air jet carries chips and fine swarf at high velocity, and air itself can be forced through a small break in the skin, producing a serious injection injury and infection. Cleaning should be done with a brush, a vacuum unit or a properly guarded low-pressure air gun with eye protection.

Question 9Occupational safety, health and environment in machine shops

Why is the metal frame of a machine tool bonded to the supply earth?

  1. It reduces the no-load current drawn by the spindle motor
  2. It gives fault current a low-resistance path to trip the breaker Correct answer.
  3. It limits the build-up of static charge on the coolant tank
  4. It raises the insulation resistance of the motor windings

Explanation

If a live conductor touches the frame, the earth bond carries fault current back to the source so the fuse or breaker operates quickly, and it holds the frame potential low while that happens. Without the bond the frame would remain live and a single touch could be lethal.

Question 10Occupational safety, health and environment in machine shops

A workshop has 200 litres of spent water-mixed cutting fluid to discard. Which disposal route complies with environmental requirements?

  1. Dilute it with water and discharge it into the workshop floor drain
  2. Burn it in the open yard behind the workshop
  3. Send it to an authorised reprocessor with a disposal record Correct answer.
  4. Pour it into the swarf skip so it leaves with the metal scrap

Explanation

Spent metalworking fluid contains mineral oil, biocides and metal fines and is a controlled waste, so it must go to an authorised recycler or treatment plant with proper documentation. Discharging to a drain, open burning or contaminating scrap metal are all illegal routes and expose the shop to prosecution.

Question 11Hand tools, measuring instruments and metrology

A vernier caliper has main scale divisions of 0.5 mm and its vernier scale is divided into 25 equal divisions. What is the least count of the instrument?

  1. 0.05 mm
  2. 0.01 mm
  3. 0.02 mm Correct answer.
  4. 0.50 mm

Explanation

Least count is the value of one main scale division divided by the number of vernier divisions, so 0.5 mm ÷ 25 = 0.02 mm. This is the smallest difference the caliper can resolve directly on the work. Always confirm the actual graduation markings on the instrument before applying the formula, because the same body casting may be fitted with a 0.05 mm or 0.02 mm scale.

Question 12Hand tools, measuring instruments and metrology

Which hand tool is used to check whether two adjacent machined faces of a workpiece are at right angles?

  1. Feeler gauge
  2. Try square Correct answer.
  3. Outside caliper
  4. Centre punch

Explanation

A try square carries a hardened steel blade fixed at exactly 90° to its stock, so holding the stock against one face and the blade against the other shows any out-of-square gap against a light source. It is a comparison tool only and gives no numerical angle in degrees. Confirming squareness before marking or machining prevents errors being carried to the next operation.

Question 13Hand tools, measuring instruments and metrology

While sawing a thin-walled pipe with a hacksaw, which blade should be selected?

  1. Fine pitch, giving two or three teeth in contact with the wall Correct answer.
  2. Coarse pitch, giving fast chip clearance through the kerf
  3. Any pitch, since pitch has no effect on thin sections
  4. Coarse pitch, reducing the number of teeth in contact

Explanation

The rule for hacksaw selection is that at least two or three teeth must be cutting at all times. On a thin wall a coarse blade straddles the section, the teeth snag on the edge and strip, so a fine pitch is chosen. Pitch is decided by the thickness of the work, not by cutting speed or material alone.

Question 14Hand tools, measuring instruments and metrology

A 0–25 mm outside micrometer with a least count of 0.01 mm shows 7.5 mm on the barrel and 28 divisions on the thimble. What is the reading?

  1. 7.28 mm
  2. 7.78 mm Correct answer.
  3. 7.50 mm
  4. 8.28 mm

Explanation

The barrel supplies whole and half millimetres, so 7.5 mm is taken first, and the thimble adds 28 × 0.01 = 0.28 mm. Adding the two parts gives 7.78 mm. The half-millimetre line must be counted whenever the thimble has uncovered it, which is the most common source of reading error.

Question 15Hand tools, measuring instruments and metrology

A dial indicator is set to zero on a rotating shaft. During one revolution the pointer swings to +0.03 mm and then to −0.04 mm. What is the total indicated reading (TIR)?

  1. 0.12 mm
  2. 0.07 mm Correct answer.
  3. 0.04 mm
  4. 0.01 mm

Explanation

TIR is the algebraic difference between the highest and lowest indicator readings, so +0.03 − (−0.04) = 0.07 mm. It expresses the full spread of eccentricity, not the amount the pointer moves away from the zero setting in one direction. Both signs must be carried into the subtraction.

Question 16Hand tools, measuring instruments and metrology

What is the correct way to join two slip gauges before use?

  1. Clean the faces and slide one gauge over the other under light pressure Correct answer.
  2. Oil the faces and press them hard together
  3. Clamp them in a bench vice until the faces touch
  4. Tap them together with a soft-faced hammer

Explanation

Wringing succeeds only on clean, flat, burr-free faces: the gauge is laid at a slight angle, slid into position and twisted with light hand pressure. The retained air film and molecular attraction between the lapped surfaces then hold the blocks together. Force or clamping distorts the lapped faces and permanently destroys the accuracy of the set.

Question 17Hand tools, measuring instruments and metrology

A hole is specified 25.000/25.021 mm and its mating shaft 24.980/24.993 mm. Which type of fit results?

  1. Interference fit
  2. Transition fit
  3. Force fit
  4. Clearance fit Correct answer.

Explanation

The largest permissible shaft, 24.993 mm, is still smaller than the smallest permissible hole, 25.000 mm, so a gap always exists. Maximum clearance is 25.021 − 24.980 = 0.041 mm and minimum clearance is 25.000 − 24.993 = 0.007 mm. Because the shaft can never exceed the hole, the assembly is a clearance fit.

Question 18Hand tools, measuring instruments and metrology

A sine bar with 100 mm between roller centres is set to 30° using slip gauges. What height of gauge combination is required?

  1. 86.60 mm
  2. 25.00 mm
  3. 57.74 mm
  4. 50.00 mm Correct answer.

Explanation

For a sine bar the setting height is h = L × sin θ, so 100 × sin 30° = 100 × 0.5 = 50.00 mm. The roller centre distance is the hypotenuse and the gauge stack forms the opposite side of the right triangle. The angle can only be trusted if the bar is set on a truly flat surface plate with the rollers parallel to it.

Question 19Hand tools, measuring instruments and metrology

A 0.02 mm vernier caliper reads 12 mm on the main scale with the 13th vernier division coinciding. The instrument has a zero error of +0.03 mm. What is the corrected reading?

  1. 12.29 mm
  2. 11.97 mm
  3. 12.23 mm Correct answer.
  4. 12.26 mm

Explanation

The observed reading is 12 mm + (13 × 0.02) = 12.26 mm. A positive zero error means the jaws already indicate 0.03 mm when fully closed, so this amount must be subtracted: 12.26 − 0.03 = 12.23 mm. Reversing the sign of the correction doubles the error instead of removing it.

Question 20Hand tools, measuring instruments and metrology

A metric gauge block set contains blocks from 1.005 mm, 0.01 mm steps up to 1.49 mm, 0.5 mm steps up to 9.5 mm, and 10 mm steps upward. Which combination builds 41.125 mm?

  1. 1.005 + 1.02 + 9.0 + 30.0
  2. 1.005 + 1.12 + 9.0 + 30.0 Correct answer.
  3. 1.005 + 1.12 + 9.5 + 30.0
  4. 1.005 + 1.12 + 8.5 + 30.0

Explanation

Blocks are built from the last decimal place backwards: the 1.005 mm block clears the thousandths, 1.12 mm then leaves a whole 9 mm, and a 30 mm block completes the stack. The total is 1.005 + 1.12 + 9.0 + 30.0 = 41.125 mm. Every step must leave a remainder that can still be made from the coarser blocks available, which is why the order matters.

Question 21Hand tools, measuring instruments and metrology

Before selecting a matching nut, a fitter must confirm the pitch of an external metric screw thread on a stud. Which hand tool is intended for this check?

  1. Radius gauge
  2. Screw pitch gauge Correct answer.
  3. Wire gauge
  4. Feeler gauge

Explanation

A screw pitch gauge carries a set of thin leaves whose tooth profiles match standard thread pitches; the leaf that seats exactly on the thread identifies the pitch. Radius gauges copy fillet radii, feeler gauges measure gaps, and wire gauges measure sheet or wire thickness, so none of them can identify a thread pitch.

Question 22Hand tools, measuring instruments and metrology

What is the purpose of the ratchet stop fitted at the end of an outside micrometer thimble?

  1. It removes backlash between the spindle and its nut
  2. It limits the measuring force applied to the workpiece Correct answer.
  3. It automatically compensates for wear of the anvil measuring faces
  4. It locks the spindle so that the reading can be noted

Explanation

The ratchet stop slips once a preset measuring force is reached, so every reading is taken at the same pressure and neither the workpiece nor the instrument is distorted. The spindle lock is a separate lever on the frame, and backlash is taken up by the adjusting nut behind the thimble, not by the ratchet.

Question 23Hand tools, measuring instruments and metrology

A vernier bevel protractor has its main scale graduated in whole degrees, and its vernier scale has 12 equal divisions occupying 11 main scale divisions. What is the least count of the instrument?

  1. 12 minutes
  2. 5 minutes Correct answer.
  3. 6 minutes
  4. 1 minute

Explanation

Least count = 1 main scale division minus 1 vernier scale division = 1° minus (11°/12) = 1°/12 = 5 minutes. The 12 vernier divisions are each 55 minutes wide, and this 5-minute difference between the scales allows angles to be read to the nearest 5 minutes.

Question 24Hand tools, measuring instruments and metrology

Which statement correctly describes the behaviour of a GO and NO-GO plug gauge set when checking a hole?

  1. The GO gauge should not enter, while the NO-GO gauge should enter
  2. The GO gauge enters freely, while the NO-GO gauge does not enter Correct answer.
  3. Both gauges must pass through the hole to at least half of their full length
  4. Both gauges are screwed into the hole and the tightening torque is measured

Explanation

The GO plug is made to the maximum material size of the hole, that is its minimum diameter, so it must enter under its own weight to prove the hole is not undersize. The NO-GO plug is made to the minimum material size, the maximum hole diameter, and must be refused; if it enters, the hole is oversize.

Question 25Hand tools, measuring instruments and metrology

A blind bore in a machine housing is to be measured using a telescopic gauge and an outside micrometer. Which procedure gives a valid bore diameter?

  1. Read the diameter directly on the telescopic gauge scale and confirm it with a steel rule
  2. Rock the gauge in the bore while reading the micrometer clamped on the workpiece
  3. Insert, lock and withdraw the gauge, then measure its contacts with the micrometer Correct answer.
  4. Set the micrometer to the nominal bore size and then force the telescopic gauge into the bore

Explanation

A telescopic gauge is a transfer instrument: its spring-loaded plungers are expanded in the bore, rocked gently to align across the true diameter, locked, and withdrawn. The distance across the two contacts is then measured with an outside micrometer, and the check is repeated at right angles to detect ovality.

Question 26Hand tools, measuring instruments and metrology

A drawing calls for a surface finish of Ra 1.6 µm on a bearing seat. What does the Ra value describe?

  1. The arithmetical mean deviation of the profile from the mean line Correct answer.
  2. The total waviness height measured over the full component length
  3. The maximum peak-to-valley height of the roughness profile
  4. The spacing between consecutive roughness peaks along the profile

Explanation

Ra is the arithmetic mean of the absolute heights of the roughness profile from its mean line over the sampling length, so both peaks and valleys contribute to the value. It is not the single maximum peak-to-valley height, nor a peak spacing, nor a waviness value.

Question 27Hand tools, measuring instruments and metrology

A metric screw thread has a 60° included angle and a pitch of 2 mm. What is the best-size wire diameter for measuring its effective diameter by the three-wire method?

  1. 1.732 mm
  2. 1.155 mm Correct answer.
  3. 1.000 mm
  4. 2.000 mm

Explanation

For a 60° thread the best-size wire touches the flanks at the pitch line, and its diameter is p divided by (2 cos 30°), which equals 0.57735p. With a pitch of 2 mm this gives 1.1547 mm, rounded to 1.155 mm.

Question 28Hand tools, measuring instruments and metrology

An outside micrometer of 0–25 mm range and 0.01 mm least count has its thimble zero line 3 divisions below the barrel reference line when the measuring faces are closed. A workpiece reading is 15.32 mm. What is the actual size?

  1. 15.29 mm
  2. 15.38 mm
  3. 15.32 mm
  4. 15.35 mm Correct answer.

Explanation

A thimble zero below the reference line means the instrument reads too small, so the zero error is negative and its amount must be added to every reading. The correction is 3 × 0.01 = 0.03 mm, giving 15.32 + 0.03 = 15.35 mm.

Question 29Fitting, assembly, alignment and scraping of machine components

While hand-scraping a machine tool slideway, the high spots are located by rubbing the work against a surface plate coated with a thin film of which medium?

  1. Kerosene
  2. Prussian blue Correct answer.
  3. Water
  4. Engine oil

Explanation

Prussian blue spotting compound is spread thinly on the surface plate; when the work is rubbed against it, the compound transfers only to the high spots. Those marked spots are scraped away and the cycle repeated until the bearing points are evenly distributed.

Question 30Fitting, assembly, alignment and scraping of machine components

A fitter must verify a 0.08 mm gap between a gib strip and the slide face before final tightening. Which measuring aid is most suitable for this check?

  1. Outside micrometer
  2. Dial test indicator
  3. Feeler gauge set Correct answer.
  4. Vernier height gauge

Explanation

A feeler gauge consists of thin, accurately ground steel leaves of known thickness, and the leaf that enters the gap with a light drag gives the clearance directly. It is the standard shop aid for checking gib and slide clearances in assembly work.

Question 31Fitting, assembly, alignment and scraping of machine components

A ball bearing with an interference fit on its inner ring must be mounted on a shaft without damage. Which assembly method is correct?

  1. Oil heating to 80–100 °C Correct answer.
  2. Pressing on the ball cage
  3. Hammering through the outer ring
  4. Cooling the shaft in water

Explanation

Uniform oil heating to about 80–100 °C expands the inner ring so that it slips onto the shaft without force and then grips as it cools. Where force is used instead, it must be applied to the ring being fitted, never transmitted through the rolling elements.

Question 32Fitting, assembly, alignment and scraping of machine components

Which scraper is most suitable for scraping the inclined faces and corners of a dovetail slideway?

  1. Diamond-point scraper
  2. Flat scraper
  3. Triangular scraper Correct answer.
  4. Half-round scraper

Explanation

The triangular (three-square) scraper has a narrow edge that reaches into the acute corners and along the sloping faces of a dovetail slide. A flat scraper is intended for open flat surfaces where its full width can bear on the work.

Question 33Fitting, assembly, alignment and scraping of machine components

A tapered gib strip has a taper of 1:100. To reduce the slide clearance by 0.05 mm, how far must the gib be advanced along its length?

  1. 0.5 mm
  2. 2 mm
  3. 50 mm
  4. 5 mm Correct answer.

Explanation

With a 1:100 taper the gib thickness changes by 1 mm for every 100 mm of longitudinal movement, so the required movement is 0.05 × 100 = 5 mm. After advancing, the gib is locked and the slide checked for free movement without shake.

Question 34Fitting, assembly, alignment and scraping of machine components

In the rim-and-face method of aligning two coupled shafts, what does the dial indicator reading on the face mainly indicate?

  1. Radial offset
  2. Bearing preload
  3. Axial end play
  4. Angular misalignment Correct answer.

Explanation

The indicator on the rim reads the radial or parallel offset between the shaft centrelines, while the indicator on the face reads the variation in gap around the coupling, which reveals angular misalignment. Both sets of readings are needed to compute the shim corrections.

Question 35Fitting, assembly, alignment and scraping of machine components

A precision spirit level is placed across the bed ways of a lathe, first near the headstock and then near the tailstock. Comparing these two cross-level readings checks the bed for which fault?

  1. Spindle concentricity
  2. Tailstock centre height
  3. Straightness in the vertical plane
  4. Twist Correct answer.

Explanation

Cross-level readings taken at two positions along the bed detect twist: equal readings mean both ends lie in the same transverse plane, while unequal readings show that one end is rotated relative to the other. Twist must be corrected by shimming or levelling screws before any alignment test is meaningful.

Question 36Fitting, assembly, alignment and scraping of machine components

A dial test indicator is swept through one full revolution on a shaft and gives a total indicator reading of 0.04 mm. What is the eccentricity of the shaft?

  1. 0.02 mm Correct answer.
  2. 0.08 mm
  3. 0.04 mm
  4. 0.01 mm

Explanation

The total indicator reading is the difference between the highest and lowest points of the circle, which is twice the eccentricity. Therefore eccentricity equals 0.04 ÷ 2 = 0.02 mm.

Question 37Fitting, assembly, alignment and scraping of machine components

After spotting against a surface plate, a slideway shows bearing spots concentrated at the four corners with very few in the middle. What condition does this reveal?

  1. Concave, with the centre low Correct answer.
  2. Twisted along the longitudinal axis
  3. Convex, with the centre high
  4. Flat and ready for finishing

Explanation

The marking compound transfers only to the points that actually bear, so spots at the four corners mean the corners are high and the centre is low, that is, the surface is concave. The corners must be scraped down until the spots spread uniformly over the whole area.

Question 38Fitting, assembly, alignment and scraping of machine components

A precision level of 0.02 mm/m sensitivity is placed on a 500 mm long machine bed and the bubble moves two divisions from zero. What is the height difference between the ends of the bed?

  1. 0.02 mm Correct answer.
  2. 0.04 mm
  3. 0.10 mm
  4. 0.01 mm

Explanation

One division represents 0.02 mm per metre, so over the 500 mm length one division equals 0.01 mm. Two divisions therefore give 2 × 0.01 = 0.02 mm of height difference between the ends.

Question 39Fitting, assembly, alignment and scraping of machine components

When hand-scraping the slideway of a precision machine tool, approximately how many bearing spots should be aimed for in each 25 mm × 25 mm square of the finished surface?

  1. 8 to 10 spots
  2. 4 to 6 spots
  3. 40 to 50 spots
  4. 20 to 25 spots Correct answer.

Explanation

Bearing-spot density is the practical measure of contact quality on a scraped slideway. For precision machine tool slideways the accepted target is about 20 to 25 spots per 25 mm square, giving a fine, evenly distributed bearing pattern. Coarser counts are used only for ordinary or rough bearing surfaces.

Question 40Fitting, assembly, alignment and scraping of machine components

The two halves of a gearbox housing have been aligned and bolted together, and taper dowel pins are then fitted. What is the main purpose of these dowel pins?

  1. To locate the two halves so that the alignment of the bearing bores is restored after the housing is dismantled and reassembled Correct answer.
  2. To clamp the joint faces together tightly enough to prevent oil leakage
  3. To provide a means of adjusting the bearing preload after assembly
  4. To carry the torque reaction of the gear shafts from one half to the other

Explanation

Dowel pins are locating elements, not clamping elements. Once the halves have been aligned, the dowels transfer that alignment permanently so the joint returns to the same position every time it is stripped and rebuilt, keeping the bearing bores coaxial.

Question 41Fitting, assembly, alignment and scraping of machine components

Before aligning a motor to a pump, a dial indicator is mounted on the base plate with its stylus on the top of one motor foot. The foot bolt is slackened and the indicator shows a change of 0.08 mm. What does this indicate?

  1. The bearing clearance in that end of the motor is excessive
  2. The motor shaft is bent by 0.08 mm at the coupling end
  3. The coupling has an angular misalignment of 0.08 mm
  4. That foot is soft or sprung and must be corrected with shims before alignment is attempted Correct answer.

Explanation

This is the soft-foot check: with the stylus on the foot, slackening the bolt releases any built-in strain. A reading change means the foot does not sit flat on its pad, so it springs the frame when tightened and will distort the alignment as the bolts are tightened. The foot must be shimmed until the indicator stays steady.

Question 42Fitting, assembly, alignment and scraping of machine components

When hand-scraping a long lathe bed way, the fitter deliberately leaves the middle of the way slightly lower than the ends. Why is this done?

  1. To allow a thicker oil film to collect so that the saddle is lubricated at mid-travel
  2. To compensate for the bed expanding more in the middle when the machine warms up
  3. To prevent a short saddle from rocking when it passes over the middle of the way Correct answer.
  4. To leave material that can be removed later when the bed is re-scraped after wear

Explanation

A saddle is shorter than the bed, so if the middle of the way were left high the saddle would rock on that high spot and lose contact at the ends, producing chatter and inaccurate work. Relieving the middle slightly keeps the saddle bearing on the end portions throughout its travel.

Question 43Fitting, assembly, alignment and scraping of machine components

A taper pin is to be fitted through a lever hub and shaft to lock them together after alignment. Which procedure gives a correct, load-carrying fit?

  1. Drill a straight hole to the small-end diameter and drive the taper pin in until it jams
  2. Drill and tap the hole, then screw in a taper pin and tighten it with a spanner
  3. Drill the hole, ream it with a taper reamer to match the pin, check the contact by blueing, then drive the pin in and lock it Correct answer.
  4. Drill the hole oversize and secure the taper pin with a parallel cotter pin through the small end

Explanation

A taper pin only transmits load properly when its full tapered length bears on a matching reamed taper. The hole is drilled undersize, reamed with the correct taper reamer, the contact checked, and the pin driven until it seats and is then secured.

Question 44Fitting, assembly, alignment and scraping of machine components

A parallel key is to be fitted between a shaft and a gear hub. Which combination of fits is correct?

  1. Tight on the sides in the shaft keyway and clearance on the sides in the hub keyway Correct answer.
  2. Clearance all round, with the key retained only by the top face
  3. Clearance on the sides in the shaft keyway and tight on the sides in the hub keyway
  4. Tight on the sides in both keyways so that the hub has to be pressed on

Explanation

The key is seated tight on its sides in the shaft keyway so that it cannot shift, while the hub keyway gives a sliding clearance fit on the sides so the hub can be assembled and removed. Load is carried on the side faces, and a small clearance is left on top.

Question 45Fitting, assembly, alignment and scraping of machine components

A dial indicator is mounted on the table of a vertical drilling machine and its stylus is traversed up the side of a cylindrical square, from 100 mm to 400 mm above the table. The reading changes from 0 to +0.06 mm. What does this show?

  1. The column is out of square by 0.06 mm per 100 mm of height
  2. The column is out of square with the table by 0.06 mm over the 300 mm checked, which is 0.02 mm per 100 mm Correct answer.
  3. The table surface is dished by 0.06 mm over the 300 mm traverse
  4. The spindle bearing has 0.06 mm of radial play

Explanation

The indicator is carried by the table, so any change as the stylus climbs the cylindrical square is the departure of the column from squareness with the table over that height. The error is 0.06 mm in the 300 mm traversed, which normalises to 0.02 mm per 100 mm.

Question 46Fitting, assembly, alignment and scraping of machine components

A six-bolt bearing cap must be tightened without distorting the bore. What is the correct tightening practice?

  1. Tighten in two or three stages, working diagonally outwards from the centre bolts Correct answer.
  2. Tighten to full torque, slacken each bolt a quarter turn, then re-torque in any order
  3. Tighten each bolt to full torque in turn, starting at one end of the cap and working along
  4. Tighten fully from the outer bolts inwards so that the cap seats at its ends first

Explanation

Staged tightening in a diagonal pattern starting at the centre spreads the clamping load evenly and lets the cap seat progressively. One-pass or end-to-end tightening tilts the cap and can distort or crack it and misalign the bore.

Question 47Fitting, assembly, alignment and scraping of machine components

A motor and pump are coupled through a flexible coupling. Dial indicator readings show the face gap at the coupling is 0.10 mm larger at the bottom than at the top, and the motor shaft centreline is 0.05 mm lower than the pump centreline. The coupling face diameter is 200 mm; the motor front foot is 300 mm and the rear foot 900 mm from the coupling centre. How much shim is required under the front and rear feet to correct both errors by raising the motor?

  1. 0.05 mm front and 0.05 mm rear
  2. 0.25 mm front and 0.55 mm rear
  3. 0.20 mm front and 0.50 mm rear Correct answer.
  4. 0.15 mm front and 0.45 mm rear

Explanation

The angular error is corrected in proportion to distance: (0.10 ÷ 200) × 300 = 0.15 mm at the front foot and (0.10 ÷ 200) × 900 = 0.45 mm at the rear foot. The parallel offset of 0.05 mm is then added at both feet, giving 0.20 mm front and 0.50 mm rear.

Question 48Fitting, assembly, alignment and scraping of machine components

Three cast-iron surface plates are hand-scraped to flatness by spotting each plate against the other two in turn, rotating the pairing, and repeating the cycle. Why is the three-plate method used?

  1. It cancels the errors of the individual plates so that all three converge on the same true plane without needing an external reference Correct answer.
  2. It deliberately produces a slightly convex surface, which is stronger than a flat one
  3. It hardens the scraped surface by repeated cold working against the other plates
  4. It reduces the amount of marking compound needed compared with spotting against a single master plate

Explanation

With only two plates, any error in one is copied onto the other and cannot be detected. Spotting each plate against both of the others makes every error show up as a mismatch somewhere in the set, so the three surfaces can only agree when all are flat, giving a true plane with no master.

Question 49Machine elements, power drives and transmission systems

In a standard V-belt drive used for a machine tool spindle, the included angle of the belt cross-section is normally:

  1. 60°
  2. 90°
  3. 30°
  4. 40° Correct answer.

Explanation

Standard industrial V-belts are made with a 40° included angle so that the belt wedges into a matching pulley groove. This wedge action raises the friction torque capacity compared with a flat belt at the same shaft tension.

Question 50Machine elements, power drives and transmission systems

A parallel key fitted between a machine tool shaft and its hub is provided mainly to:

  1. limit the maximum shaft speed
  2. absorb angular misalignment between the hub and shaft
  3. carry axial thrust along the shaft
  4. transmit torque between the shaft and hub Correct answer.

Explanation

A parallel key sits in matching keyways and transmits torque by shear and bearing pressure between the shaft and hub. It is not intended to resist axial thrust or to accommodate misalignment.