Fig 10 shows a pillar drill press used in a school design and technology workshop for drilling holes in metal and plastic workpieces. (a) Calculate the over...

(a) The overall gear ratio of the compound spur gear train is found by multiplying the individual stage ratios:

\[ \text{Stage 1 ratio} = \frac{\text{Driven teeth}}{\text{Driver teeth}} = \frac{40}{20} = 2 : 1 \]

\[ \text{Stage 2 ratio} = \frac{60}{20} = 3 : 1 \]

\[ \text{Overall gear ratio} = 2 \times 3 = 6 : 1 \]

[1] for each stage ratio, [1] for the correct overall ratio. In a compound gear train, the output shaft of the first stage is mechanically linked (on the same shaft) to the input gear of the second stage, so the ratios multiply rather than add.

(b)(i) The output speed of the drill spindle:

\[ \text{Output speed} = \frac{\text{Input speed}}{\text{Overall gear ratio}} = \frac{2800\,\text{rpm}}{6} = 466.7\,\text{rpm} \]

[1] for the correct method, [1] for the correct answer (accept 467 rpm). The motor speed is divided by the overall ratio to give the spindle speed.

(b)(ii) A compound gear train achieves a large speed reduction in a compact space. [1] A single pair of spur gears with a 6:1 ratio would require the driven gear to be six times the diameter of the driver, making it impractically large for the drill's column housing. Splitting the reduction across two stages keeps all gears small.

(c)(i) The electric motor produces rotary motion. [1] The motor shaft spins continuously around its axis.

(c)(ii) When the operator pushes the lever handle downward, the drill chuck produces linear motion. [1] The chuck and drill bit travel in a straight line downward into the workpiece.

(d)(i) The mechanical advantage of the lever handle:

\[ \text{MA} = \frac{\text{Effort distance}}{\text{Load distance}} = \frac{250\,\text{mm}}{50\,\text{mm}} = 5 \]

[1] for the formula, [1] for the correct answer. The operator applies force at 250 mm from the pivot and the load acts at 50 mm, so the output force is five times the input force.

(d)(ii) The drill press uses a Class 2 lever. [1] The fulcrum is at the pivot where the handle mounts to the column, the load (drill resistance) acts at the pinion close to the fulcrum, and the effort (operator's hand) is applied at the far end of the handle. In a Class 2 lever, the load is always between the fulcrum and the effort.

(d)(iii) A sketch of the drill press lever arrangement:

[1] for the correct lever arrangement with load between fulcrum and effort, [1] for clear labels on all three elements.

(e)(i) Two meshing spur gears:

[1] for correct gear shapes with teeth, [1] for opposite rotation arrows (driver clockwise, driven anti-clockwise), [1] for correct labels. The teeth mesh at the point of contact, and the driver pushes the driven gear in the opposite rotational direction.

(e)(ii) Spur gears are simpler to manufacture and produce no axial thrust along the shaft. [1] When the shafts are already parallel, spur gears transmit motion efficiently without the complexity and cost of bevel gears, which are designed for shafts at an angle.

(f)(i) Bevel gears transmit rotary motion between shafts at right angles. [1] (Also acceptable: worm gear or mitre gear.)

(f)(ii) Bevel gears are used in a hand drill to change the direction of rotation by 90 degrees, allowing the drill bit to turn at right angles to the handle crank. [1] (Also acceptable: car differential, angle grinder, food mixer.)

(g) Two mechanical properties required of the return spring material:

1. High elasticity (resilience): the spring must return to its original shape after being compressed or extended repeatedly, without taking a permanent set (plastic deformation). [1]
2. High tensile strength: the spring must resist the repeated stress cycles of the drilling operation without fracturing or developing fatigue cracks. [1]

(Also acceptable: corrosion resistance, fatigue resistance, good hardness.)

(h)(i) The depth stop prevents the drill bit from travelling too far through the workpiece, which could damage the worktable surface, break the drill bit, or cause the workpiece to lift off the clamp. [1] It also allows consistent hole depths to be set when producing a batch of identical components, ensuring dimensional accuracy across repeated operations. [1]

(h)(ii) Two safety precautions:

1. Always clamp the workpiece securely in a machine vice or with a G-clamp before drilling, to prevent it from spinning with the drill bit and striking the operator. [1]
2. Wear safety goggles to protect the eyes from flying metal swarf and debris produced during drilling. [1]

(Also acceptable: tie back loose hair and remove loose clothing or jewellery; use the guard; select the correct drill speed for the material; remove the chuck key before starting the motor.)