ITI Fitter Interview Questions and Answers

What is the least count of a vernier caliper?

Least count = value of one main-scale division minus value of one vernier-scale division. On the common metric vernier, 49 mm is divided into 50 vernier divisions, so one vernier division is 0.98 mm and the least count is 1 − 0.98 = 0.02 mm. Some verniers read to 0.05 mm.

How to say it: Give the formula and the 0.02 mm working, then read the instrument they hand you.

What is the least count of an outside micrometer?

Pitch of the spindle screw divided by the number of thimble divisions: 0.5 mm ÷ 50 = 0.01 mm.

What is zero error, and how do you correct it?

Close the jaws or anvils fully. If the zero lines do not coincide, the instrument has a zero error: positive if the reading is above zero, negative if below. Subtract a positive error from every reading and add a negative one.

How to say it: Always check zero before measuring. Say that you do it every time.

What is a try square used for?

To check that two surfaces are at 90° to each other, to check flatness against light, and to mark lines at right angles to an edge.

What are a surface plate, V-block and scriber used for?

The surface plate is the flat reference surface for marking out and checking. A V-block holds round work for marking and drilling. The scriber marks lines on metal. A dot punch (commonly 60°) makes witness marks along lines; a centre punch (90°) marks the centre for drilling.

Which types of files do you know?

By grade of cut: rough, bastard, second cut, smooth and dead smooth. By cut: single cut, double cut and rasp. By shape: flat, hand, square, round, half round, triangular and knife. Bastard files remove metal quickly; smooth files finish. Draw filing gives a fine finish at the end.

How do you choose a hacksaw blade?

By the number of teeth per inch. Coarse blades suit soft metal and thick sections; fine blades suit thin sheet and tubes, because at least three teeth should be in contact with the work. Fit the blade with the teeth pointing forward. It cuts on the forward stroke.

How to say it: "At least three teeth in contact" is the rule supervisors listen for.

What is the point angle of a standard twist drill?

118°, for general work in steel.

What tap drill size is used for an M10 thread?

For a metric coarse thread, tap drill ≈ major diameter minus pitch. M10 has a 1.5 mm pitch, so 10 − 1.5 = 8.5 mm.

How to say it: Give the formula, then the number. It lets you answer for any size they ask.

In what order do you use a set of hand taps?

Taper tap first to start the thread, then the second (intermediate) tap, then the plug (bottoming) tap to cut full thread to the bottom of a blind hole. Use cutting oil and turn back regularly to break the chip.

What is the difference between drilling and reaming?

Drilling makes the hole. Reaming removes a small amount of metal from a drilled hole to bring it to an accurate size with a smooth finish.

What is tolerance?

The permitted variation in a size: upper limit minus lower limit. For 25 ± 0.05 mm, the limits are 25.05 and 24.95, and the tolerance is 0.10 mm.

What types of fit are there?

Clearance fit (the shaft is always smaller than the hole, so it can move), interference fit (the shaft is always larger, so it is pressed or shrunk in), and transition fit (it may be either). In the hole-basis system the hole size is kept fixed (H), and the shaft is varied: H7/g6 is a clearance fit, H7/p6 an interference fit.

How do you fit and remove a bearing?

Press on the ring that has the tight fit (the inner ring when it goes on a shaft) using a sleeve or a press, never by hitting the outer ring or the balls. Remove it with a bearing puller. Keep it clean and lubricate as specified.

How to say it: "Never hammer through the balls" shows you have done it.

What is preventive maintenance?

Scheduled checks done before a breakdown: lubrication, tightening, cleaning, checking alignment, belt tension and wear, and replacing parts at fixed intervals. Breakdown maintenance is repair after failure.

What safety do you follow on a bench grinder?

Check the wheel for cracks before mounting, keep the guard in place and the tool rest close to the wheel, wear goggles, stand to one side when starting it, and never grind on the side of a straight wheel.

Why are gloves not worn on a drilling machine?

A glove can catch on the rotating drill or chuck and pull the hand in. Clamp the work in a vice, not by hand, and keep loose sleeves and hair away.

How do you mark out a job?

Clean the surface and apply marking medium, file two datum edges square, then scribe every line from the datums with a height gauge or odd-leg caliper and steel rule, and punch witness marks along the lines.

How to say it: Mention datum edges: measuring everything from a datum is what keeps the job accurate.

What is the usual practical test for a fitter?

A filing job to a drawing: for example a male and female fit (square, step or dovetail) to a given tolerance. File the datum faces square, mark out, hacksaw close to the line, file to size, check often with the try square and vernier, deburr, and check the fit at the end.

How to say it: Check size often; a job filed undersize cannot be saved.