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
different
speeds
of
the
produced
gearbox
is
in
intermediately
4.2
(i.e.;
between
four
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,
relatively
low,
which
to
have
thus
be
uI1 the
and
uI2
(i.e.
differences
transmitted
is
low
0.4
and
between but
0.5)
the
then
u I3
are
torques 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
teeth
fast
caused
by
failure the
because
torque
of
fatigue
transmitted
on
between
the
gear
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
