Machining and Cutting Tools Questions and Answers

Answer: C

Morse standard tapers run from 0 to 7.

The Morse taper series has eight sizes, numbered MT0 (the smallest) to MT7 (the largest). They are used on drill shanks, lathe centres, tailstock and drilling machine spindles, and sleeves let a smaller taper fit a larger socket.

Numbering from 1 leaves out MT0, and there is no MT8 in the standard series, so 1 to 7, 1 to 8 and 0 to 8 are all wrong.

Answer: D

The half included angle of a Morse taper is about 1 degree 29'.

Morse tapers are close to 1 in 20 on diameter, about 0.05 mm per mm. The half angle is

\[ \begin{aligned} \tan \theta &= \frac{1}{2 \times 20} = 0.025 \\ \theta &\approx 1^\circ 26' \end{aligned} \]

and it varies slightly between the Morse numbers, from about 1°25' to 1°30'. That is the angle to which the compound rest is swivelled to turn a Morse taper. The 3 degree options are about twice that, close to the included angle of the taper, not half of it.

Answer: C

Pipes of more than 63 mm and up to 200 mm are held in a chain pipe vice.

A chain pipe vice grips the pipe between serrated jaws and a chain wrapped round it and tightened, so one vice can hold a wide range of large diameters securely for cutting and threading.

The ordinary hinged pipe vice, with V-shaped jaws, is made for the smaller pipe sizes. A pipe wrench grips and turns a pipe; it does not hold the pipe still while it is worked on. So 'All of above' is wrong.

Answer: B

The job reciprocates in planing.

On a planer the large, heavy workpiece is clamped to a table that moves back and forth under a stationary single-point tool, which is fed sideways at the end of each stroke. This suits long, heavy jobs that would be awkward to cut with a moving tool.

In shaping it is the other way round: the work is fixed and the ram carrying the tool reciprocates horizontally. A slotting machine is a vertical shaper, again with the tool on a reciprocating ram. So 'All of the above' is also wrong.

Answer: A

The order is Tungsten, Chromium, Vanadium.

The classic 18-4-1 high speed steel (grade T1) contains about 18% tungsten, 4% chromium and 1% vanadium, with carbon around 0.7%. Tungsten gives red hardness, the ability to keep its hardness at the high temperatures of cutting; chromium improves hardenability; vanadium forms very hard carbides that resist wear and refine the grain.

Vanadium is the smallest constituent and chromium the middle one, so every order that does not start with tungsten and end with vanadium is wrong.

Answer: D

Shapers commonly use the crank and slotted link mechanism.

A bull gear carries a crank pin and sliding block that runs in a slotted link (rocker arm) pivoted at its lower end. As the bull gear turns at uniform speed, the crank sweeps a larger angle during the forward (cutting) stroke than during the return stroke, so the ram returns faster and less time is wasted on the idle stroke.

Bevel gears change the direction of a drive, a pawl and ratchet gives intermittent motion (it is used for the cross feed of a shaper), and a worm and worm wheel gives a large speed reduction. None of them produces a quick return.

Answer: C

A shaper is specified by the stroke of ram.

The size of a shaper is given by the maximum length of stroke of its ram, for example a 450 mm shaper, because that sets the longest cut, and so the largest job, the machine can take. Fuller specifications add the motor power, the number of speeds and the table size, but the stroke length is the defining figure.

The bed size, the tool head and the quick return speed ratio are details of the machine, not how it is specified. (A lathe, by contrast, is specified by its swing and the distance between centres.)

Answer: A

Cast iron is machined with dry air.

Cast iron is normally machined dry. The free graphite flakes in it act as a built-in lubricant, and the chips come off as small, broken fragments and dust rather than long ribbons. A jet of compressed air is used to clear the chips and cool the cutting zone.

Water-based coolants and oils mix with cast iron dust to form an abrasive sludge that clogs the machine and slideways. Kerosene is used on aluminium, and machine (cutting) oil on steels, especially for threading and heavy cuts.

Answer: D

The answer is All of the above.

Cemented carbide (tungsten carbide grains bonded with cobalt) keeps its hardness up to about 1000°C, against roughly 600°C for high speed steel. Because it is more heat resistant, it can be run at higher cutting speeds, often three to five times those of HSS, and at a given speed it wears more slowly, giving longer tool life.

Each of the first three options is a true advantage, so none of them alone is the full answer. Carbide's drawback is brittleness: it chips under shock and interrupted cuts, which is why it is usually used as brazed tips or inserts rather than solid tools.

Answer: C

The ratio of cutting time to return time is 2.

In the crank and slotted lever mechanism, the extreme positions of the slotted lever occur when it is tangent to the crank circle, which makes a right angle between the crank and the lever. If the return stroke takes a crank angle \(\beta\), then

\[ \begin{aligned} \cos\frac{\beta}{2} &= \frac{\text{crank}}{\text{centre distance}} = \frac{200}{400} = 0.5 \\ \frac{\beta}{2} &= 60^{\circ}, \quad \beta = 120^{\circ} \end{aligned} \]

The cutting stroke takes the rest of the turn, \(360^{\circ} - 120^{\circ} = 240^{\circ}\). At uniform crank speed, the time ratio is \(\frac{240}{120} = 2\). The 2000 mm length of the slotted bar affects the length of the stroke, not the time ratio, so it is not needed here.