2016 question 7 (Machining)

Question 1

identify three safety features integrated into a lathe

Answer 1

emergency stop button

leadscrew guard

emergency foot break pedal

chuck interlocking guard

screen attached to the main saddle

Question 2

Explain how measurement errors may occur when using digital vernier callipers

Answer 2

battery could be weak

locknut might be loose

jaws maybe damaged

callipers might be on zero when jaws are open

Question 3

outline 1 use of a vee-block and clamp

Answer 3

to hold round metal rod/pipes for performing drilling or milling operations

Question 4

distinguish between a pilot hole hole and a tapping size hole

Answer 4

A pilot hole is drilled before a larger hole is drilled

A tapping size hole is a hole drilled before threading

Question 5

explain the difference between a rake angle and a clearance angle in cutting tools

Answer 5

Rake angle is the angle of the cutting face relative to the workpiece

Clearance is formed to allow one point of the the cutting tool to contact the workpiece

Question 6

Outline 2 reasons why a sealed lubrication system is used in engineering machines

Answer 6

Heat will be spread around

Reduces friction between moving parts of machines

machine parts will last longer

Sealed systems make sure that lubrication materials dont escape

Question 7

identify any 2 lubricating materials commonly used in engineering machines

Answer 7

Oil

PTFE

Grease

Graphite

Question 8

Outline 2 advantages and two disadvantages of an interchangeable tungsten carbide insert

Answer 8

Advantages:
will retain their cutting edge at high temperatures
they are interchangeable
inserts can have multiple cutting tools in their design

Disadvantages:
they break easily
they are expensive

Question 9

indicate whether CNC machining or manual machining is most suitable for each of the following applications. Justify your selection in each case:

(i) .The production of plumbing fittings
(ii) .Customized pieces for a chess set
(iii) Repair of damaged alloy wheels

Answer 9

The production of plumbing fittings:
CNC machining as plumbing fittings are mass produced in high volume

Customized pieces for a chess set:
Manual Machining because accuracy may not be essential

Repair of damaged alloy wheels:
Manual machining will be more efficient as wheels may be damaged to a greater or lesser extent

Question 10

Describe briefly how the tungsten carbide inserts are manufactured

Answer 10

Carbon black, tungsten metal and metal oxides are mixed and heated until the carbon bonds with the tungsten (carbruises)

Mix the tungsten carbide powder with wax and cobalt.

This is mixed using a ball mill to give you a final powder

final powder is put into a mould and pressed into desired shape

Heat the pressed, final powder enough so that is sticks together.

Put the piece in a specialized oven for the final sinter where the powder cooks, shrinks and gets very hard,