Machining Exam Questions

Question 1

Describe the function of a reamer in machining

Answer 1

A reamer is a type of rotary cutting tool used in metalworking.
Precision reamers are designed to enlarge the size of a previously formed hole by a small amount but with a high degree of accuracy to leave smooth sides.
The process of enlarging the hole is called reaming.

Question 2

Outline the uses of a v-block and clamp

Answer 2

They are precision metalworking jigs typically used to hold round metal rods or pipes for performing drilling or milling operations.

Question 3

Explain why a three jaw chuck is not suitable for holding a square bar

Answer 3

A three-jaw chuck has its jaws at 120 degrees whereas a square bar has its sides at 90 degrees. Therefore the qquare bar will not be held on centre in a three-jaw chuck.

Question 4

Explain the difference between a dovetail cutter and a slot drill in milling

Answer 4

Dovetail cutter will machine an angled profile suitable for dovetail joints.
Slot drill will machine a slot in the middle of a piece to a certain depth or it can also machine an edge profile.

Question 5

Give three reasons why it may be necessary to operate drilling machines at different speeds

Answer 5

The diameter of the drill bit used
The type of material being drilled
Feed rate of the drill bit

Question 6

Give five safety hazards associated with the use of a centre lathe in the engineering classroom

Answer 6

1. Rotating workpieces at high speed - chuck guards need to be used.
2. Metals can get hot - use cutting fluids if needed, ensure lathe cutting tools are in good condition.
3. Cutting metal swarf is sharp - do not allow to build up and dispose of carefully.
4. Rotating shafts can catch loose clothing - ensure guards are in place.
5. Inexperienced users need supervision.

Question 7

Explain the difference between a clearance hole and a tapping size hole in drilling

Answer 7

Clearance hole is a hole through an object which is large enough to enable threads of a screw or bolt to pass through but not the head of the screw or bolt.

A tapping size hole is drilled to allow threads to be cut on the inside of the hole.

Question 8

Explain ways in which cutting fluids help the machining process

Answer 8

Cutting fluids will keep the material and cutting tools cool, this prevents heat build up and improves cutting action.
Most cutting fluids have some lubricating action to make cutting more efficient.

Question 9

Outline reasons for dressing a grinding wheel

Answer 9

Wheel dressing is used to restore the cutting surface of any irregularities.
Grinding wheels are designed to have self-dressing action in which grains should break free and expose sharp edges.
Wheel dressing will renew a sharp cutting face and correct irregularities such as wheel concentricity, loaded and glazed wheels.
The process can remove any undulations from the wheel.

Question 10

Identify some safety features integrated into a lathe

Answer 10

Emergency stop button 
Chuck interlocking guard 
Leadscrew guard
Emergency foot brake pedal
Screen attached to the main saddle

Question 11

Name some important properties of cutting tool materials

Answer 11

Cutting tools must be harder than the material being machined.
Cutting tools must maintain a sharp edge at high temperatures generated by the machining process.
Cutting tools need to have the ability to be sharpened or replaced easily.
Able to withstand the shock loads of machining processes.

Question 12

Describe the factors that influence metal machinability

Answer 12

The term machinability refers to the ease with which a metal can be machined to an acceptable surface finish.

The condition of the work material includes factors such as microstructure, grain size, heat treatment, chemical composition, fabrication, hardness, yield strength and tensile strength.
Physical factors include the modulus of elasticity, thermal conductivity, thermal expansion and work hardening.

Other important factors are operating conditions, cutting tool material and geometry and the machining process paramenters.

Question 13

List 6 functions of cutting fluid

Answer 13

1. reducing the build-up of heat.
2. Washing chips and swarf away from the cutting edge.
3. May have lubrication action to improve machining and surface finish.
4. reduces vibration in machine.
5. prolongs tool and machine life.
6. allows higher cutting speeds.

Question 14

Explain the difference between generating and forming. Give examples of both.

Answer 14

Generating: moves the tool in various directions until the required surface is machined. Facing and taper turning on the lathe are examples of machining by generation.

Forming: is when the surface produced is a copy of the tool producing it. Contour work and screw cutting are examples of forming.