Question 1 [5 marks]

a) Describe with the aid of simple sketches in your answer booklet, what are the most likely types

of gearing inside each of the gearboxes shown below (i) to (vi). Only those shafts that emerge

from the gearbox have been shown (other shafts may exist inside the gearbox).

b) Calculate the gear ratio associated with each gearbox.

?i = 100 RPM

?o = 40 RPM

?i = 100 RPM

?i = 100 RPM

?o = 100 RPM

?i = 100 RPM

?o = 100 RPM

?i = 1200 RPM

?i = 100

RPM

?o = 4RPM

i) ii)

iii) iv)

v) vi)

?o = 100 RPM

?o = 60 RPM

Question 2 [12 marks]

BEARING DESIGN

a) What is the probability of survival (i.e. percentage of non-failed bearings) for a L10 life?

b) What is a separable bearing?

c) Briefly explain why a bearing with a cylindrical roller generally has a greater load bearing

capacity than a bearing with a ball rolling element.

d) In a hydrodynamically lubricated bearing what is meant by the term embedability?

BELT/CHAIN DESIGN

The following questions are based on a belt selection chart (below) presented in lectures based on

Australian Standards 2784.

e) Arrow “A” indicates that for increasing transmitted power the belt size should generally

increase; why does the belt size generally increase as power increases?

f) Arrow “B” indicates that for increasing shaft speed the belt size should generally decrease;

why does the belt size generally decrease as shaft speed increases?

MOTOR SELECTION

g) What is the meaning of locked rotor torque?

h) Provide an example of a design scenario that is suited to a NEMA D electric motor.

CLUTCH / BRAKE DESIGN

i) What is the technical difference between a clutch and a brake?

j) Is an assumption of constant pressure, or constant wear more appropriate for a brand new

(unused) clutch.

SHAFT DESIGN

k) AS 1403 provides design equations for calculating shaft diameter; are these equations

based on Von-Mises or Tresca failure criteria?

l) AS 1403 requires that steel be used and does not allow the use of aluminium. What property of

aluminium makes it undesirable for shaft design?

m) Table 2 from AS 1403 is provided below. What is the meaning of the term FS in Table 2?

n) Table 2 from AS 1403 is provided below. From Table 2, which of the Formulas use Yield

Strength (rather than endurance limit) as the failure criterion?

GEAR DESIGN

o) Fill in the blanks in the following statement of the law of gearing.

“The common normal to the tooth profiles at the point of contact must always pass

through ___________________ on the line of _______.”

p) In the following image showing the terminology used for tooth definition, four terms

(A,B,C and D) are hidden. What are the terms A, B, C and D?

DE-MOUNTABLE CONNECTOR DESIGN

q) What is the name given to describe a joint where the screws clamp the plates together so firmly

that load is transferred without any direct shear being applied to the screws?

r) A spline is often used to allow shaft translation. What is the failure mode of such a spline (i.e.

what design rule do we use to ensure the spline functions correctly)?

s) Name one advantage and one disadvantage of connecting two shafts with a flexible coupling.

Question 3 [9 marks]

The initial stages of a gear design are complete with the following data given:

Npinion = 17 teeth

Ngear = 68 teeth

?pinion = 1750 RPM

m = 6 mm

Tpinion = 75Nm

Km = 2.2

Ko = 1.75

With reference to the design charts and tables below answer the following questions

a). Does the design provide a hunting tooth ratio?

b). What is the pitch diameter of the pinion?

c). What is the approximate worst-case value of the velocity factor Kv for the pinion if the pinion is

“Precision, shaved and ground”?

d). What is the (AGMA) geometry factor, J, for the pinion for 20 degree full depth teeth?

e). What is the value of Ft?

f). A reasonable estimate of the bending strength (St) of a high carbon nickel chromium vanadium

steel (such as 4130) is 700MPa. If we make the pinion from 4130 steel what minimum face width b

do we require to avoid fatigue failure due to bending?

BENDING STRESS

Question 4 [9 marks] IF YOU COMPLETE THIS QUESTION, YOU SHOULD NOT

COMPLETE QUESTION 5.

A 600mm radius brake drum contacts a short shoe, as shown below, and sustains a braking torque

of 550Nm. For a co-efficient of friction of 0.25 determine:

(a) The total normal force, N, on the shoe required to achieve the braking torque.

(b) The force required, W, to apply the brake when the rotation is in the clockwise direction?

(c) The required force, W, to apply the brake when the rotation is in the counter-clockwise

direction?

(d) A revised dimension “x” required to make the brake self-locking, assuming all other

dimensions remain as shown. In which rotational direction of the drum is self-locking achievable,

i.e. W = 0 ?

W

Question 5 [9 marks] IF YOU COMPLETE THIS QUESTION, YOU SHOULD NOT

COMPLETE QUESTION 4.

Four M12 (i.e 12mm diameter) bolts secure the flanges of a rigid coupling to each other. The bolts

are on a pitch circle of 100 mm diameter. The threaded portion of the bolts does not traverse the

interface between the flanges.

a) Determine the maximum torque the coupling may transmit if the maximum permitted value

of shear stress in the bolt material is 80 MPa.

For bolt groups experiencing torsional shear loading

?

?

( )

T r

2 A r

?

b) Discuss with the aid of sketches at least four failure modes that a designer should consider

when determining the necessary proportions of the bolts and flange geometry.