UNTUK RUJUKAN SAHAJA. JANGAN MENIRU. JADILAH UMAT YANG SUKA

BERFIKIR UNTUK KEBAIKAN DAN KEKUATAN ISLAM.

KJM 561: Sessional Assignment 1

EM220 / 7M2

Date: 9/4/2005 UiTM Shah Alam

TITLE: MACHINE TOOL GEARBOX DESIGN.

This gearbox design is actually the interpretation of the

available gearbox configuration of a cutting machine. The

arrangement of the gearbox gears was taken from a catalogue

at UiTM machine shop.

For my case of study, I have chosen the eight speeds

Cholchester 5 ½ in. (140 mm) Bantam Lathe. The diagram of

the machine is shown in the Appendix.

Figure 1 shows the gearbox layout of the lathe

machine. It consists of three major shafts with the input

or driving shaft denoted by C.

As shaft C act as the input shaft, it consists of four

gears for speed changing mechanism with number of teeth of

12, 30, 14 and 24 respectively. On the intermediate shaft,

denoted as D, four gears mounted on it. Each gears having

number of teeth of 30, 13, 28, and 20 respectively.

On the output shaft A, two major gears acting on it

which have number of teeth of 44 and 51 respectively. Shaft

B and E act as reversing shafts for the system. Furthermore

the arrangement of the gearbox is in 4.2 (i.e.; four

different speeds produced intermediately between shaft C

and D whilst two different speeds between shaft D and A).

As a summary, number of teeth of the gears involve in

the mechanism can be categorized as follows:

Shaft C:

N11 = 12 (= a)

N12 = 14 (= c)

N13 = 24 (= e)

N14 = 30 (= g)

Shaft D:

N21 = 30 (= b)

N22 = 28 (= d)

N23 = 20 (= f)

N24 = 13 (= h)

Shaft A:

N31 = 51 (= i)

N32 = 44 (= k)

From Figure 1, the first stage transmission ratio has four

combinations:

uI1 = N11/ N21 (= 12/30)

= 0.4

uI2 = N12/ N22 (= 14/28)

= 0.5

uI3 = N13/ N23 (= 24/20)

= 1.2

uI4 = N14/ N24 (= 30/13)

= 2.3

Figure 1: Gearbox layout of 8 speeds Cholchester Bantam

Lathe.

The second stage transmission ratio then has two

combinations which are:

uII1 = N23/ N31 (= 20/51)

= 0.39

uII2 = N22/ N32 (= 28/44)

= 0.64

The speed layout or the Ray Diagram of the gearbox is shown

in Figure 2.

Figure 2: Speed layout of eight speeds gearbox.

The step ratio of the gearbox can be calculated as follows:

B = speed range

φ = step ratio

z = number of speed

nH = the highest speed

nL = the lowest speed

B = φ (z-1)

= nH/ nL

= 800/36

= 22.222

φ = 22.2221/7

= 1.56

which give the speeds as follows :

n1 = 36 rpm

n2 = 36 (φ) (= 56.16 rpm)

n3 = 36 (φ2) (= 87.61 rpm)

n4 = 36 (φ3) (= 136.67 rpm)

n5 = 36 (φ4) (= 213.21 rpm)

n6 = 36 (φ5) (= 332.60 rpm)

n7 = 36 (φ6) (= 518.86 rpm)

n8 = 36 (φ7) (= 800.00 rpm)

Speeds of shaft D by each gear as referred to Figure 2 are:

nII1 = n1 + (n2-n1)/2

= 46 rpm

nII2 = n3 + (n4-n5)/2

= 112 rpm

nII3 = n5 + (n6-n5)/2

= 273 rpm

nII4 = n7 + (n8-n7)/2

= 659 rpm

Speed of the input gear on shaft C as referred to Figure 2

is:

nI1 = n4 + (n5-n4)/2

= 175 rpm

Because of the space requirement, we can see that the

gearbox designed is very simple rather than because of its

number of speeds is only eight. The gearbox also using the

sliding gears as the type of speed changing mechanism.

From Figure 2,

The overall transmission ratio at stage 1 = φ6

= 14.41

The overall transmission ratio at stage 2 = φ

= 1.56

On the first stage, uI1 and uI2 (i.e. 0.4 and 0.5) are

relatively low, thus the differences between the torques

which have to be transmitted is low but then uI3 and uI4

(i.e. 1.2 and 2.3) are relatively high, thus the required

torque is also high. On the second stage, both

transmissions ratio are low (i.e. 0.39 and 0.64).

The first speed of the gearbox is provided by the

combination of gear a.b and gear f.i. When switching to the

second speed, second stage meshing gear is then changed to

gear d.k. To change to the third speed, first stage meshing

gear changed to the combination of gear c.d and gear f.i on

the second stage while fourth speed is the combination of

gear c.d and gear d.k. The next speeds are following the

same sequence.

It can be said that, to change the speed, the gear on

the output shaft has to be changed every time, thus this

will cause fast failure because of fatigue on the gear

teeth caused by the torque transmitted between gears on

different shafts. This means that speed range is supplied

by different set of gear set (i.e. to change the speed,

gear set has to be changed at stage 1 and stage 2).

The transmission ratio of the second stage is φ, and

thus this is very preferable since it is low. The highest

transmission ratio, i.e. the greatest speed change occurs

in the first part drive. Therefore the gears for reduction

uI1 must be strong enough.

Appendix

a. Eight speeds Cholchester 5 ½ in. Bantam lathe machine

b. The assembly of the eight speeds gearbox of

Cholchester 5 ½ in. Bantam lathe

c. Separated parts drawing of eight speeds gearbox of

Cholchester 5 ½ in. Bantam lathe machine