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 American Journal of  
Food Science and Technology (AJFST)

Design and Development of  an Engine Driven Onion Grading Machine 
Wabi Tafa1*, Adesoji M. Olaniyan2

Volume 2 Issue 2, Year 2023
ISSN: 2834-0086 (Online)

DOI: https://doi.org/10.54536/ajfst.v2i2.1503
https://journals.e-palli.com/home/index.php/ajfst

Article Information ABSTRACT

Received: April 03, 2023

Accepted: May 30, 2023

Published: August 21, 2023

Onion (Allium cepa, L.) is one of  Ethiopia’s highly cultivated vegetable crops. Farmers across 
the country sell their onions without grading them, which results in post-harvest losses 
during packing and transporting. As a result, modern technologies like engine-operated 
grading systems are essential. So, the design and development of  an onion grading machine 
was undertaken at Asella Agricultural Engineering Research Center (AAERC). The physical 
and mechanical properties of  the selected onion bulb variety were considered during the de-
sign. The developed grader consists of  the mainframe, feeding hopper, grading unit, outlets, 
power source, and power transmission system. The cost of  the grader was estimated to be 
20,880.99 ETB and believed that it is simple in design, easy in operation, and found to be 
suitable for small and medium-scale farmers.

Design, Development, 
Onion, Onion Grader, 
Manufacturing Process

1 Oromia Agricultural Research Institute, Asella Agricultural Engineering Research Center, Asella, Oromia, Asella, Ethiopia 
2 Department of  Agricultural and Bioresources Engineering, Faculty of  Engineering Ikole-Ekiti Campus, Ikole-Ekiti 370001, 
  Ekiti State, Nigeria
* Corresponding author’s e-mail: wabitafa@gmail.com

INTRODUCTION 
Onion (Allium cepa L.) is a member of  the Allium 
genus of  the Alliaceae family. It is thought to have 
originated in southwestern Asia, which was the center of  
domestication and variability. It is from this place that it 
spread worldwide and has been cultivated annually for 
bulb production for over 4700 years (Brewster, 2008). 
The introduction to Africa in general, and Ethiopia 
specifi cally, was not well-known. However, it has been 
suggested that as introduced by foreigners in the early 
1970s and by now produced widely in many parts of  the 
country than the traditionally grown shallot (Adgo, 2008).
In Ethiopia, onion is one of  the most important vegetable 
crops grown on a small scale. It is also one of  the most 
economically important vegetables in the country. The 
area under onion is gradually rising, owing to its high 
profi tability per unit area and ease of  production, and the 
expansion of  small-scale irrigation regions (Nigussie et al., 
2015). It ranked second in the production of  all vegetable 
crops next to Tomato, which has been concentrated in the 
central rift valley of  the country, particularly in the upper 
Awash and Lake Batu areas (Bossie, 2009). In Ethiopia, 
the crop is used extensively in food fl avoring and everyday 
stews, as well as in various vegetable food preparation 
uses. Despite its year-round production settings, the 
crop’s yield and productivity are much below (10.02 t/ha) 
the world average (19.7 t/ha) (FAO, 2012). Because of  
the lack of  improved cultivars, the use of  inappropriate 
agronomic practices such as pre-harvest and post-harvest 
management practices, and a lack of  attention/awareness 
about the benefi ts of  intensive production, the low yield 
results indicate that there is a huge gap in production 
and productivity in the country. In onion production, 
postharvest losses are widespread due to the perishable 
nature of  the onion and the lack of  proper postharvest 
practices and processing technology, which is a major 

production restriction that reduces productivity. The 
major causes, according to the fi ndings, are primarily 
related to technical limitations in harvesting techniques, 
handling, conveying, packing, storage, and cooling 
facilities in diffi cult climatic conditions, infrastructure, 
and marketing systems (Gebru, 2015). 
Similarly, several studies identifi ed the most common 
causes of  postharvest losses as a lack of  sorting and 
grading to eliminate defects before storage. Demand for 
onion has increased over the years and so is its quality. 
After the harvest of  onions, their quality is important to 
the fi nal consumer. Damage-free post-harvest handling 
is regarded as a necessity for increasing the farmer’s 
profi t margin in in-freshly eaten commodities like an 
onion.Grading is the process of  classifying materials 
into various homogeneous groups based on specifi ed 
qualities such as size, shape, colour, and quality (Londhe 
et al., 2018). It lowers handling losses during transport and 
saves time and energy in various processing procedures. 
Grading also facilitates packing, marketing, and other 
post-harvest procedures. Grading agricultural products, 
particularly fruits and vegetables, according to their size 
is an important value-adding technique that increases the 
market value required for cross-border trade (Charles and 
Etiese, 2020). According to the World Trade Organization 
(WTO), new marketing trends need high-quality graded 
items. Uniformity in size makes the product more 
attractive to consumers and also improves its processing 
qualities. In a developing country, most fruit and vegetable 
growers grade their products by hand. Grading by hand 
is expensive and the operation is hampered by labour 
shortages during high seasons. Human operations can be 
ineffi cient, inconsistent, and time-consuming. Farmers 
are hoping for suitable agricultural product grading 
equipment to help ease labour shortages, save time, and 
improve the quality of  graded products (Mostafa, 2004).

Keywords



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In Ethiopia, onion growers are the major actors who 
perform most value chain functions from farm inputs 
preparation to post-harvest handling and marketing 
(Agidew, 2018). Farmers sell their onion produce without 
grading which leads to post-harvest losses during packing 
and transporting. Also, they receive a lower price for their 
produce. However, manual size grading of  onion crops is 
practiced by whole-sellers and retailers thereby, they make 
a higher profi t than farmers. Manual grading is labor-
intensive, inconsistent, time-consuming, less effi cient, 
and not standardized. To achieve a uniform size of  onion 
bulbs proper grading mechanism is required, and with 
the aid of  a grading machine, that goal can be achieved 
(Aher et al., 2019). Different fruit and vegetable grading 
machines have been developed worldwide. Divergent 
roller type, expanding pitch type, inclined vibrating plate, 
and counter-rotating roller with inclination type graders 
are developed for grading fruit and vegetables depending 
on size basis(Charles and Etiese, 2020). In Ethiopia 
persons engaged in postharvest handling of  crops have 
no chance to use imported high-cost size separation 
and grading techniques. Such high-grading equipment 
is not useful to small-scale farmers because of  the high 
cost of  the machine, high cost of  operation, and more 
maintenance cost. Small-scale farmers and wholesalers 
are in crucial need of  low-cost graders. Various types of  
onion grading machines suitable for small-scale farmers 
were developed using different design approaches. 
However, these machines are with some limitations related 
to functional requirements, safety aspects, portability, 
and ease of  operation which affects the performance of  
the machine. Mainly, the problem observed with those 
machines were a high percentage of  onion bulb damage, 
low capacity, the rigidity of  the design, and also the power 
source they used is not suitable for the farmers in our 
country who mostly have no access to electricity. In order 
to solve this, the present study work was carried out to 
design and develop an onion grading machine while 
taking into account the needs of  the local market and 
the lack of  suitable low-cost onion grading equipment for 
small and medium-scale farmers. 

MATERIALS AND METHODS
Description of  Experimental Site
To fulfi ll objectives, the designing and manufacturing 
of  the onion grading machine prototype was conducted 
in the Asella Agricultural Engineering Research Center 
(AAERC) which is located in Oromia National Regional 
State, Ethiopia. It is located at 6° 59’ to 8° 49’ N latitudes 
and 38° 41’ to 40° 44’ E longitudes, having an elevation 
of  2430 meters above sea level.

Design Principles and Considerations
To design and fabricate a suitable machine, machine 
design parameters were considered before the design 
and fabrication of  the machine. Therefore, designs 
parameters consider to be important were as follows 
(Khurmi & Gupta, 2005);

The kinematics of  the machine: The successful operation 
of  any machine depends largely upon the simplest 
arrangement of  the parts which give the motion required. 
Selection of  materials: A designer must have a thorough 
knowledge of  the properties of  the materials and 
their behavior under working conditions. Some of  the 
important characteristics of  materials are strength, 
durability, fl exibility, smoothness, weight, resistance 
to heat and corrosion, ability to be casted, welded, or 
hardened, machinability, electrical conductivity, etc. 

Design and Analysis of  Machine Components 
The machine was designed to grade onion bulbs into three 
distinct size ranges small (<40 mm), medium (40-60 mm), 
and large-sized (>60 mm) bulbs according to the size of  
onion bulbs with three rotating cylinders having parallel 
bars spacing of  different dimensions. These categories of  
size were made based on international standards of  the 
marketable size of  onion bulbs suitable for commercial 
applications (Ashraf, 2007). The main components of  
the onion bulbs grader prototype designed and developed 
were: Feeding hopper, concentric cylindrical grading unit, 
pulleys and belts, bearings, power source, and supporting 
frame as shown below in Figure 1.

1-Feeding rate; 2-Top cover; 3-Rotating shaft; 4-Pulley; 
5-Belt; 6-Engine; 8-Speed reduction pulley; 9-Ground 
wheel; 10-Collection outlets; 11-Grading unit; 12- 
Mainframe; 13- Handle

Figure 1: Pictorial view of  the fabricated onion grading 
machine prototype.

Figure 2: Exploded view of  the various components of  
an onion grading machine.



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              a = base width (m)
              b= Length of  the hopper (m)
The designed volume of  the hopper is 0.09 m3 is greater 
than the theoretical volume (0.073 m3) determined by 
equation 2. Therefore, the designed dimensions of  the 
hopper are valid.

Main Frame
The frame is the skeletal structure of  the grader which 
forms the platform on which other components are 
mounted. The total weights carried by the frame are; the 
weight of  the feed hopper, weight of  the grading unit, 
weight of  the collection tray, weight of  the shaft, the 
weight of  bearings, pulleys, and the belt. The two design 
factors considered in determining the material required 
for the frame were weight and strength. The machine 
frame was constructed from steel angles and rectangular 
pipe of  50×30×3 mm. Two rubber wheels were provided 
on one end to simplify the transportation of  the machine. 
The frame and other parts of  the grading machine were 
connected using appropriate sizes of  bolts and nuts and 
the welding process.

Design of  Feeding Hopper
The hopper was designed using a mild steel sheet 
with a 1.5mm thickness. The size of  the hopper was 
determined on the basis of  mass and volumetric capacity 
of  the maximum feeding rate and average bulk density of  
ungraded onion bulbs. The inclination of  the hopper was 
designed based on the angle of  repose of  onion bulbs 
(Ukey & Unde, 2010). A trapezoidal shape of  the hopper 
was used for the machine due to consideration of  the free 
fl ow of  onion bulbs. The bottom of  the hopper is slightly 
tilted downwards to enhance the fl ow of  onion bulbs 
directly to the center of  the rotating cylinder. The hopper 
has a sliding gate to control the feed rate. The following 
parameters were considered for the design of  the hopper; 
Angle of  repose = 46.30, Bulk density of  onion bulbs = 
549.7 kg/m3. Then theoretically, it was assumed to hold 
at least 40 kg onion bulbs as the maximum feeding rate 
of  the machine was 35 Kg/min and the volume of  the 
hopper was calculated by the following formula according 
to Begum (2018).

Vh=1.1VO                                                              (1)                 
Vo=Wo/ρbulk                                                                 (2)
Vh=1.1((40 kg)/(549.7 kg/m3 ))=0.073 m3

Where:
               Vh = volume of  hopper, (m3)
               Vo= volume of  onion bulbs, (m3)
               Wo= weight of  onion bulbs, (kg)
               ρ_bulk= bulk density of  onion bulbs, (kg)
Therefore, the required volume of  the hopper is 0.073 m3

Figure 3 show the shape of  the hopper was designed in a 
trapezoidal shape and we can get the practical dimensions 
by assumptions. Hence, here also it was assumed that the 
hopper has a square in size with base width (a) =0.3 m, 
length of  the hopper (b) =0.5 m, and height (h) =0.45 m, 
and its volume was calculated by Equation 3 (Charles and 
Etiese, 2020);
   Vdh=1/2 (a+b)×h×b                                       (3)
        =1/2 (0.3+0.5)×0.45×0.5=0.09 m3

Where:
           Vdh = the designed volume of  the hopper, (m3)
              h = height of  the hopper, (m)

Figure 3: Isometric view of  the hopper (all dimensions 
are in mm)

Grading Unit
The grading unit was designed using a mild steel rod, 
mild steel fl at bar and mild steel shaft consisting of  three 
cylindrical sieves having parallel bars cells. The rotating 
cylinders are arranged one inside the other according 
to the size (the larger spacing being internal, while the 
smaller one being external) and shown below in Figure 
4. The ungraded onion bulbs are directed to the internal 
cylinder and the larger size bulbs are graded directly and 
collected at the end of  the internal cylinder, while the 
medium and smaller size bulbs are dropped down to the 
second cylinder for further grading and the medium bulb 
size onion bulbs are left on this second cylinder collected 
at the end. 
Finally, the bulbs with smaller sizes are going to the 
third sieve or cylinder and are collected at its end. The 
cylindrical sieves are fi xed on the driveshaft and fi xed with 
the machine frame. The volume of  the rotating cylinders 
can be determined based on the fl ow of  granular material 
through a circular shape. Many researchers suggested 
that the diameter of  the rotating cylinder could be varied 
between 200 and 550 mm depending on the size range of  
the fruits and vegetables, volume, and desired capacity of  
the grading unit (Dereje, 2019; Charles and Etiese, 2020; 
Hegazy and Mady, 2018; Gunathilake et al., 2016). For 
this design, the dimensions of  the internal cylinder were 
850 mm long and 250 mm in diameter with a spacing of  
60 mm. The middle cylinder has 650 mm long and 350 
mm in diameter with a spacing size of  40 mm, and the 
external cylinder has 450 mm in length and 450 mm in 
diameter with a spacing size of  20 mm. 
The length of  the rotating cylinders was decided by 
considering the previously developed rotating type 
graders and by assuming that the dimensions can provide 
enough path and time of  retention for onion bulbs to be 
graded.



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Am. J. Food. Sci. Technol. 2(2) 1-13, 2023

kg=5.76 kg 
By using the same procedure we have used above we can 
compute the mass of  rods on the middle cylinder;
Where:
The density of  the rod, ρ=7850 kg/m3, 
The radius of  a rod, r = 0.005 m, 
Length of  the medium cylinder, h = 0.65 m, 
The diameter of  the middle cylinder, Dmc=0.35 mm, 
Spacing between rod on the cylinder, S=0.05 m, and 
Number of  rods required = 22
m=22(ρ×v)=23(ρ×πr2 h)
=22(7850×π(0.005)2×0.65)
=22×0.40075 kg=8.813 kg
Mass of  rods on the external cylinder, 
Where:   ρ=7850 kg/m3, 
              The radius of  a rod, r = 0.005 m, 
              Length of  the external cylinder, h = 0.45 m, 
             The diameter of  the external cylinder, Dec=0.45 
mm, 
Spacing between rod on the cylinder, S = 0.03 m, and
Number of  rods required = 50
m=47(ρ×v)=47(ρ×πr2 h)
=47(7850×π(0.005)2×0.45)
=47×0.2774 kg=13.04 kg

Mass of  Rolled Flat Bar
According to Charles and Etiese, (2020) the mass of  rolled 
fl at bar used for each rotating cylinder was calculated;
  mfb=ρ×v                                                           (7)
Where:  mfb= mass of  rolled fl at bar (kg), 
           ρ = density of  the fl at bar (kg/m3) 
               =7850kg/m3, and
           v = volume of  rolled fl at bar (m3).
But, v=πr2 h                                                                                                                                     
Where: v = volume of  the rolled fl at bar (m3),    
             r= radius of  the rolled fl at bars used for each 
rotating cylinder (0.125 m, 0.175 m, and 0.225 m for the 
internal, middle, and external cylinder respectively), and 
            h = thickness of  the fl at metal bar (m)
               = 3 mm=0.003 m
v=πr2 h
= 2 ( π × 0 . 1 2 5 2× 0 . 0 0 3 ) + 2 ( π × 0 . 1 7 5 2× 0 . 0 0 3 ) + 2
(π×0.2252×0.003)
=0.001826 m3

mfb=ρ×v=(7850 kg)/m3 ×0.001826 m3=14.33 kg
Also, the mass of  the bushing and round bar used to 
attach the cylinder with a rotating shaft is 1.467 kg. So, the 
total mass of  the rotating cylinder (mrc), was estimated as;
mrc=msr+mfb=5.76+8.813+13.04+14.33+1.467
      =43.41 kg
And the weight (W) of  the grading unit is also determined 
from Eqn. (8).
   W=mrc g                                                             (8)
      = 43.41 kg x 9.81m/s = 425.85 N
Where:     W = weight of  the grading unit (N), 
                  mrc = mass of  rotating grading cylinder (kg), 
and
                  g = acceleration due to gravity (9.81m/s2).

Figure 4: The grading unit: (a). Front; (b). Right; (c). 
Bottom; (d). Isometric view (all dimensions are in mm)

Weight of  Grading Unit
The mass of  the rotating cylindrical grading unit was 
determined from the volume and density of  the mild 
steel rod and rolled mild steel fl at bar materials used to 
manufacture the grading cylinder (Charles and Etiese, 
2020). Based on previous work recommendations related 
to material selection to minimize bulb damage the mild 
steel rod having a diameter of  10 mm was used for all 
cylinders and arranged with different spacing and lengths 
as mentioned above. Also, the rolled fl at bar with different 
diameters was welded with the steel rods and constitutes 
the overall mass of  the rotating cylinders. 

Mass of  Mild Steel Rod
The mass of  rods on the internal rotating cylinder was 
determined using Eq. (4) (Charles and  Etiese, 2020). 
m=ρ×v                                                                (4)
Where:
 m=Mass of  mild steel rod (kg);
 ρ = density of  mild steel rod (kg/m3) 
    = 7850 kg/m3; and
  v =volume of  mild steel rod (m3)
But, 
 v=πr2h                                                                 (5)
v=πr2h=π(0.005)2×0.85=0.000066758 m3

m_sr=ρ×v=7850×0.000066758=0.524 kg
Where: 
           v = volume of  the rotating cylinder (m3)
           r= Radius of  the rod (m) = 0.005 m
           h = length of  the internal cylinder (m) = 0.85m
Also, the number of  rods required for each cylinder was 
estimated by using equation (6)(Kankal, 2013);
     Ns=(πDrc)/S                                                            (6)
Where: 
   Ns = numbers of  mild steel rods per segment
   Drc= Diameter of  the internal rotating cylinder (0.25 m)
  S = spacing between rod on the cylinder (0.06+0.01= 
0.07)
Number of  rods required for the cylinder, 
N=(π(0.25))/0.07= 11
Therefore, the mass of  rods on the cylinder, m=11×0.524 



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Theoretical Analysis of  the Grading Unit
To determine the power required to move onion bulbs 
through the rotating grading unit it is important to consider 
the process by which ungraded onion bulbs are delivered 
from one end of  the inclined rotating cylinder and try to 
reach the other end of  the cylinder. During this process, 
onion bulbs at the lower portion of  the cylinder are lifted 
upward by the screen surface, after which they are again 
lifted along with it and slide down. They gradually move 
toward the opposite end of  the cylinder. The bulbs are in 
contact with only a part of  the cylindrical surface with no 
relative movement with respect to it during their lifting. 
The nature of  the motion of  onion bulbs over the surface 
of  the cylindrical sieve depends upon the coeffi cient of  
friction on the given surface. The kinematics operating 
condition is governed by centripetal acceleration (rω2), 
the initial conditions of  motion of  the bulbs, the point 
at which they are delivered onto the grading surface 
(grading cylinder), and their initial velocity. Depending 
upon the relationship between the above factors, the 
bulbs in the cylinder may slide along with it, separated 
from its surface, and perform a free fl ight or may move 
with the surface being at rest relative to it. In the last case, 
the bulbs are not graded (Bosoi et al. 1991). Neglecting 
the sliding motion of  the onion bulbs inside the cylinder, 
the release of  onion bulbs through the cylindrical grader 
depends upon the relative velocity and the forces acting 
on each bulb.
The weight of  onion bulbs is directed downward and the 
centrifugal force is given below (Abd El-Tawwab et al., 
2012).
      Wo=mg                                                            (9)
       Fc = m r ω2                                                      (10)
Where:
            Wo = weight of  the onion bulbs (N),
             m = mass of  the onion bulbs (kg),
            Fc= the centrifugal force (N),
            g = acceleration due to gravity (9.81m/s2), 
         r = the radius of  the internal cylinder to which 
ungraded onion bulbs were applied fi rst (0.125 m),
           ω = the angular speed of  the rotating cylinder (s-1). 
The motion of  the bulb on the cylinder surface is not 
determined by the tangential forces alone. But, if  the 
resultant of  the normal forces (Nf) is not directed towards 
the cylinder surface, the bulb will lose contact with the 
cylinder.
To fi nd the equation that describes the motion of  the 
onion bulbs through the rotating cylinder (Figure 5), it 
can be found:
Nf=mrω2+mgcosά…… in the normal direction (at ӯ ӯ)      
(11)
 mg sin ά=μNf  ………… in the tangential direction 
(at ẋ ẋ)   (12)
Where:
         Nf  = normal force (N), 
         ά = is the angular position of  the onion bulb on the 
cylinder surface measured from the horizontal axis in the 
direction of  rotation (degree), 

         μ= coeffi cient of  friction between the onion bulb 
and the cylindrical surface, 
By substituting (Nf) from equation (11) into equation (12) 
according to Abd and Magda (2011) then:
mg sinά =μ(mrω2+mg cosά )                                       (13) 
(mg sinά )/μ=m(rω2+mg cosά )                              (14) 
μrω2= g sinά -μ g cosά                                                (15)
ω2=(g sinά -μ g cosά  )/μr                                              (16)
ω2=g/μr (sinά -μ cosά)                                               (17)
ω=√(g/μr (sinά -μ cosά )                                            (18)
But,     ω=(2πNc)/60                                                   (19)
Where (Nc) is the number of  revolutions of  the rotating 
cylinder. From equation (18) and equation (17) we get:                                          
Nc=60/2π √(g/μr (sinά -μ cosά)                                 (20)
At,  α’=90^0
Nc=60/2π √(g/rμ) or  Nc=30/π √(g/rμ)                             (21)

Figure 5: The forces acting on the onion bulbs situated 
on the internal cylinder surface.

The behavior of  an onion bulb depends on the cylinder’s 
angular speed at a given radius with other factors such 
as onion bulb layers and internal friction that affect the 
performance of  a grading machine. Let us determine the 
above factors as a certain value of  (K) that ranged from 
0.33 to 0.40 according to Abd El-Tawwab et al., (2012). 
Then equation (21) may be equal to;
Nc=30/π K√(g/μr)                                                        (22)
Given that, g = 9.81 m/s2, r = 0.125 m, μ = 0.29 (the 
measured static friction angle was 16.25 degree), and let 
k=0.40 (the maximum value from above range) and by 
substituting in equation (22).

The number of  rotations per minute (Nc) found above 
is the critical speed at which falling ends and onion bulb 
remains in constant grading cylinder contact, held there 
by centrifugal force. The rotating cylinders are set inclined 
to the horizontal plane, to improve the internal pressure 
forces during the rotation of  the mass of  the onion bulbs. 
In this study, the slope angle of  the rotating cylinders 
on the horizontal plane (6°) was selected according to 
Charles & Etiese (2020).



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Also, the normal force, torque, angular speed, and power 
required to move onion bulbs in rotating cylindrical 
surfaces were found by using Eqns. (11), (23), (24), and 
(25) (Khurmi and Gupta, 2013).
T=Nf r                                                                           (23) 
ω=(2πNc)/60                                                                (24)    
=(2π×62.95)/60=6.60  rad⁄s , so
T=541.03×0.125=67.63 N.m 
PO=Tω                                                                        (25)
=67.63×6.6=446.35 Watts
Where:- PO = power required to move the onion bulbs 
through the rotating cylinder (Watts), 
T = torque required to drive grading cylinder (Nm), 
ω = angular velocity (rad/s),   
Nc = rotational speed of  the grading cylinder (62.95 
rpm), and 
 r = radius of  grading cylinder (0.125 m).

Rotational Torque of  the Rotating Cylinder
The torque developed by a rotational body was estimated 
by multiplying the Force (Fc) causing the motion by the 
radius of  rotation (r) of  the rotating cylinder (Hannah 
and Stephens, 2006).
T=Fc×r                                                                      (26)
Where:
Fc = centrifugal force required to produce acceleration 
(N) and r = radius of  rotation (radius of  the rotating 
cylinder). But,
Fc=ma=mω2 r                                                             (27)
Where: 
m = mass of  the rotating cylinder (kg),
ω = angular speed (rad/sec), 
Nc = rotational speed of  the rotating cylinder (62.95 rpm) 
based on the value from equation (21), and
r = radius of  rotational cylinder = 0.125 m.
ω=(2πNc)/60=2π×62.95/60=6.60 rad/sec
So, Fc=mω2 r=43.41×(6.60)2×0.125=235.80 N
The torque on the rotating cylinder was;
T=Fc×r=235.80×0.125 =29.48 Nm
The power required by the rotating cylinder was 
determined using the equation below as developed by 
Khurmi and Gupta, (2008).
PC=(2πNc T)/60                                                             (28)
=(2π×62.95×29.48)/60=194.30 Watts
The power required to overcome air resistance was 
determined by Eqn. (29) (Sale et al., 2016).
PAR=Kf×Fr×Vt

2                                                          (29)
Where:
PAR= power required due to air resistance, (Watts),
Kf= constant which is equal to 0.06 (Sale et al., 2016),
Fr= feed rate, 35kg/min = 0.5833 kg/s,
Vt

2= peripheral or tangential velocity of  the grading 
mechanism (m/s)
Nc = rotational speed of  the grading cylinder (62.95 
rpm), and 
r = radius of  cylinder (0.125mm).
Vt=Nc×π/30×r                                                       (30)
Vt=62.95×π/30×0.125 m

Vt= 0.83 m/s
Then, the power requirement due to air resistance PAR will 
be;
PAR=0.06×0.5833kg/s ×(0.83 m/s)2

PAR= 0.0238 kW = 23.80 Watts

Power Transmission and Drive System
Selection of  Pulley and Speed Reduction
The pulleys used in the drive system were groove-
type pulleys made of  cast iron. Pulley diameters were 
selected based on the need to reduce the engine speed 
to the required one. The power transmission system was 
designed to reduce the engine output shaft speed from 
1400 rpm to 87.5 rpm of  the grading unit rotating shaft. 
During the test, the engine throttle valve was used to 
adjust the rotating speed to an optimum level. The power 
reduction was designed in 
2 stages and fi nally, the pulleys shown in Figure 6 were 
selected. Two-speed reduction stages are given below: The 
speed ratio was calculated by using Eqn. (46) (Khurmi 
and Gupta, 2005).
Speed ratio=  N1/N2 =D2/D1                                        (31)
Where: 
D1= diameter of  the driving pulley on the engine shaft(m),
D2= diameter of  the driven pulley on the speed reduction 
shaft(m),
N1= speed of  the engine pulley (1400 rpm), and
N2= speed of  the driven pulley on the speed reduction 
shaft (rpm)

First Stage Speed Reduction
In the fi rst stage of  reduction, the driving and driven 
pulley has been selected. Assume the diameter of  the 
driving pulley with a speed ratio of  3.33: 1. From Eqn. 
(31) the diameter and speed of  the driven pulley were 
computed as follows.
D2/D1 =3.33=D2/0.075= D2=0.249 m, an available 
pulley of  250 mm diameter was selected. So, the speed 
of  the counter pulley on the speed reduction system was 
calculated using the following formula (Khurmi & Gupta, 
2005).
N1/N2 =D2/D1 =N1 D1=N2 D2, N2=N1*D1/D2 
=(1400*0.075)/0.25= 420 rpm, hence, in the fi rst 
reduction stage engine speed was reduced from 1400 rpm 
to 420 rpm.

Second Stage Speed Reduction
In the second stage, speed was reduced by using a small 
size pulley mounted on the freely rotating shaft with a 
speed ratio of  4.8:1. Then, the diameter and speed of  
the pulley mounted on the rotating grading cylinder shaft 
were calculated as follows (Khurmi and Gupta, 2005).
D4/D3 =4.8 =D4/0.075= D4=0.36 m = 360 mm.
Also, the speed of  the driven pulley was calculated as 
follows.
N3/N4 =D4/D3 =N3 D3=N4 D4,N4=N3*D3/D4 
=(420*0.075)/0.36= 87.5 rpm, In the second stage of  
speed reduction speed was reduced from 420 rpm to 87.5 



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rpm.
Where: 
D3= diameter of  the driving pulley on the speed reduction 
shaft (m),
D4= diameter of  the driven pulley on the grading unit 
rotating shaft (m),
N3= speed of  the driving pulley on the speed reduction 
shaft (420 rpm), and
N4= speed of  the driven pulley on the grading unit 
rotating shaft (rpm).
Therefore, in power transmission, engine speed was 
reduced by two stages from 1400 rpm to 87.5 rpm for 
grading operation. Further material selection and design 
calculation related to the driving pulley on the speed 
reduction shaft and driven pulley mounted on the grading 
unit rotating shaft used for the grader power transmission 
system was computed as follows.
The width of  the pulley (face width) “B” is usually 
considered to be 25% greater than the width of  belt (b) 
and Eqn. (32) (Richard and Nisbett, 2011) can be used to 
estimate the width of  the pulley. According to IS:2494-
1974 top width of  an “A” type v-belt for a 75 mm pulley 
diameter is 13 mm. So,
B=b+0.25b=1.25b
=13+0.25×13=16.25 mm
The thickness (t) of  the driving and driven pulley rim for 
a single v-belt can be determined using Eqn. (33 or 34) 
(Richard and Nisbett, 2011).
t1=D3/300+2mm                                                    (33)
=75/300+2mm=2.25 mm=0.00225 m
t2=D4/200+3mm                                                    (34)
=360/200+3mm=4.8 mm=0.0048 m
Where:
B = width of  pulley (mm),
b = width of  belt (mm), 
t1 = rim thickness of  the driving pulley on the speed 
reduction rotating shaft (mm),
t2 = rim thickness of  the driven pulley on the grading unit 
rotating shaft (mm),
D3 = diameter of  driving pulley on the speed reduction 
rotating shaft (m) = 0.075 mm, and
D4 = diameter of  driven pulley on the grading unit 
rotating shaft (m) = 0.360 mm
The weight of  the pulley was computed using the 
following equations (Thet et al., 2019).
Wp=m×g                                                                (35)
m=ρ×V                                                                  (36)
V=AP×t                                                                  (37)
Where:
Wp= Weight of  the pulley (N),
m = mass of  pulley (kg),
g = acceleration due to gravity (9.81 m/s2),
ρ = density of  the cast Iron pulley (kg/m3) = 7,200 kg/
m3, 
v = volume of  the fl at bar (m3),
AP= Area of  pulley material (m2) = (πd2/4),
d= Diameter of  pulley (m), and
t= rim thickness of  the pulley (m).

So, for a driving pulley;
V=(πd2/4)×t=(π×0.0752)/4×0.00225=9.94×10-6  m3

m=ρ×V=7200×9.94×10^(-6)=0.0716 kg
Wp=m×g=0.0716 ×9.81=0.7021 N
Also for the driven pulley, we have;
V=(πd2/4)×t=(π×0.362)/4×0.0048=4.88×10-4  m3

m=ρ×V=7200×4.88×10(-4)=3.5 kg
Wp=m×g=3.5 ×9.81=34.5 N
The velocity ratio between two pulleys transmitting 
torque is given as:
ω3/ω4 =N3/N4 =D4/D3                                                           (38)          
Where:
ω3= angular velocity of  the driving pulley,
ω4 = angular velocity of  the driven pulley,
N3= rpm of  a driving pulley (420 rpm),
N4 = rpm of  the driven pulley,
D3 = diameter of  a driving pulley (75 mm), and
D4 = diameter of  driven pulley (360 mm).
N3/N4 =D4/D3 ,N4=(N3×D3)/D4 = 87.5 rpm
ω3/ω4 =N3/N4 ,  ω3=(2πN3)/60=(2×π×420)/60=43.98  
rad⁄s
ω4=(ω3×N4)/N3 =(43.98×87.5)/420=9.16 rad⁄s

Figure 6: Detail dimension and isometric view of  smaller 
and larger pulley.

Selection of  the Belt
Classical V-belt and groove-type pulley arrangements 
were used in this work to transmit the power required 
by the grading machine (Figure 7). The main reasons for 
using the v-belt drive are its fl exibility, simplicity, and low 
maintenance costs. Additionally, the v- belt can absorb 
shocks thereby mitigating the effect of  vibratory forces 
(Khurmi and Gupta, 2005).

Determination of  Belt Contact Angle
The belt contact angle(φ) is given by the following 
equation(Khurmi and Gupta, 2005).
 φ=sin-1((D4-D3)/2x)                                                   (39)
Where: φ = belt contact angle (rad),
D3 = diameter of  driving pulley on the speed reduction 
rotating shaft (m) = 0.075 m,
D4 = diameter of  driven pulley on the grading unit 
rotating shaft (m) = 0.36 m, and
x = distance between the pulleys from center to center.
The distance between the pulleys from center to center 
was determined by using Eqn. (40) (Khurmi and Gupta, 
2005). 
x=((D4+D3)/2)+D3                                                  (40)



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Figure 7: Geometry of  V-belt drive

=((0.36+0.075)/2)+0.075=0.2925 m
Hence, the belt contact angle (φ) is computed as;
φ=sin-1(D4-D3)/2x)
=sin-1(0.36-0.075)/(2×0.2925)=29.150=29.15×π/180=0.
5 rad
The wrap angle on the smaller pulley is determined using 
Eqn. (56) while that of  the larger pulley was determined 
by using Eqn. (41) (Akintunde et al., 2005).
θ1=180-2 sin-1(D4-D3)/2x)                                           (41)
θ1=180-2 sin-1(0.36-0.075)/(2×0.2925))=121.69o

=121.69×π/180=2.12 rad
θ2=180+2 sin-1)(D4-D3)/2x)                                        (42)
θ2=180+2 sin-1(0.36-0.075)/(2×0.2925))=238.3o

=238.3×π/180=4.16 rad
Where: θ1= angle of  wrap of  a belt on driving pulley (rad) 
and
              θ2 = angle of  wrap of  a belt on driven pulley (rad) 

Determination of  Belt length
The nominal pitch length of  the belt from the speed 
reduction shaft to the grading cylinder was determined 
to know the actual belt size needed to transmit power 
the reduced power to the grading cylinder. Therefore, 
according to Khurmi and Gupta (2005)
the nominal pitch length (L) was determined using Eqn. 
(43).
L=π/2 (D3+D4 )+2x+(D4-D3 )

2/4x                          (43)
L=π/2(0 .075+0.36)+2×0.2925+(0.36-0 .075) 2/
(4×0.2925)=1.330 m
Hence, according to IS: 2494-1974, the belt of  the nearest 
standard pitch length (1331 mm) was selected.
Where: 
D3 = diameter of  a driving pulley (mm), 
D4 = diameter of  driven pulley (mm), and 
x = center distance between the motor pulley and rotating 
cylinder shaft pulley (mm) 

Determination of  Belt Tensions
The driving pulley was considered for the calculation 
of  tensions in the V-belt because the pulley of  a smaller 
diameter governs the design. According to IS: 2494-1974 
dimensions of  “A” type v-belt for 75 mm pulley diameter 
is; top width, b = 0.013 m, thickness, t = 0.008 m, bottom 
width, w = 0.011 m, length of  the belt, L=1.331 m, the 
density of  rubber belt, ρ=1140 kg/m3, coeffi cient of  
friction, μ = 0.25 and the allowable stress,  σa= 2.5 MPa 
(Khurmi and Gupta, 2005).

The peripheral velocity, V of  the belt on the driving 
pulley is:
V=r×ω3                                                                      (44)
V=0.0375×43.98 =1.65 m/s
Where: 
V= the peripheral velocity of  the belt on the driving 
pulley (m/s),
r = radius of  the driving pulley, and 
ω3= angular velocity of  a belt on the speed reduction 
driving pulley (rad/s).
The mass of  the belt, m was given by;
m=cross sectional area ×length×density                         (45)
m=b×t×L×ρ                                                             (46)
m=0.013 m×0.008 m×1.331 m×1140 kg/m3= 0.1578 kg
Where; m is the mass of  the belt.
The centrifugal tension, Tc between the contact pulley 
face and belt is given by; 
Tc=mv2                                                                           (47)
=0.1578 kg×(1.65 m/s)2 = 0.43 N
The maximum allowable tension in the belt was 
determined as;
Tmax=σa×A                                                                      (48)
=2.5 N/mm2 ×104 mm2=260 N
Therefore, the tension in the tight side of  the belt, T1 was 
computed as;
T1=Tmax-Tc                                                                         (49)
T1=(260-0.43)N=259.57 N 
Where: 
T1 = tension in the tight side (N), 
Tc  and Tmax = the centrifugal and maximum tension of  
the belt (N) respectively,
A = cross-sectional area of  a belt (mm2), 
m = mass per unit length of  a belt (kg/m), and
σ = maximum allowable stress of  belt (MPa).
Tension in the slack side of  the belt, T2 was calculated as 
follows (Khurmi and Gupta, 2005).
ln(T1/T2 )=μ×θ1×Cosecβ                                               (50)
Where:
T1 = tension of  the belt on the tight side (N), 
T2 = tension of  the belt on the slack side (N), 
μ = coeffi cient of  friction between the belt and the pulley 
(0.25), 
θ1 = lap angle on driving pulley (2.12 rad), and 
β = groove angle (18o).
ln(T1/T2 )=0.25×2.12×Cosec18
(259.57 N)/T2 )=e1.715

((259.57 N)/T2 )=5.557
5.557 T2=25
T2=46.77 N

Design of  Grading unit Driving Shaft
The shaft transmitting power under various operating 
and loading conditions can be designed based on the 
strength or rigidity principle (Richard and Nisbett, 2011). 
The shaft would be subjected to fl uctuating torque 
and bending moments during operation under load 
conditions. Shock and fatigue factors were therefore 
taken into consideration. To determine the diameter of  



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the grading cylinder shaft; all forces acting on the shaft 
(weight of  grading cylinders, weight of  maximum feeding 
rate of  onion, tight side and slack side tensions of  the 
belt, and weight of  pulley) were considered. From Eqns. 
(8, 9, 35, 49, and 50), the weight of  grading cylinders, the 
weight maximum feeding rate of  onion bulbs, the weight 
of  the pulley, and the tight side and slack side tensions of  
the belt were determined as 425.85 N, 343.35 N, 259.57 
N, 46.77 N, and 34.5 N, respectively. Shear force and 
bending moment diagrams on the vertical and horizontal 
planes were determined by considering the inclination of  
the rotating grading unit shaft to the horizontal plane. For 
rotating shafts, where the load is suddenly applied (minor 
shock) the combined shock and fatigue factor applied to 
the bending moment is given as 1.20 to 2.00 while the
combined shock and fatigue factor applied to the 
torsional moment is given as 1.00 to 1.50 (ASME, 1995). 
The diameter of  the rotating shaft was determined by 
computing the force acting on the shaft in a vertical and 
horizontal direction as shown below in Figure 8.

Figure 8: Free body diagram of  all forces acting on the 
shaft.

Where: 
RAH = horizontal bearing reaction force at A (N),
RAV  = vertical bearing reaction force at A (N), 
RBH  = horizontal bearing reaction force at B (N), 
RBV  = vertical bearing reaction force at B (N), 
Wp = weight of  pulley (N), 
WGC = weight of  grading cylinder (N),
WO= weight of  onion bulbs (N), and
Tb = total belt tension (N).

Figure 9: Free body diagram forces on the shaft on the 
vertical plane.

Forces Acting on Grading unit Driving Shaft on 
Vertical (YZ) Plane
Analysis of  vertical forces acting on the shaft as shown 
in Figure 9below.
The reactions, R_AV and R_BV were determined by 
taking moment about A;
∑MA=0
1.35×340.8N1.1×RBV+0.425×168.67N+0.325×162.6 
N+0.225×144.3 N=0
1.1×RBV=1.35×340.84 N+0.425×168.67 N+0.325×162.6 

N+0.225×144.3 N
RBV=617.13/1.1=561.03 N
Also, the summation of  all vertical forces is;
∑FV=0
RAV-167.75 N-161.71 N-143.51 N+RBV-338.97 N=0
RAV+RBV= 167.75 N+161.71 N+143.51 N+338.97 N
RAV+R_BV=811.94 N, but, RBV=561.03 N
RAV=(811.94 -561.03)N=250.91 N
The shear force and bending moment diagram on the 
main shaft due to loading is shown in Figure 10.

Figure 10: Shear force and bending moment diagram in 
the vertical plane.

Forces Acting on Grading unit Driving shaft on 
Horizontal (XZ) Plane
Analysis of  horizontal forces acting on the shaft as shown 
in Figure 11.

Figure11: Free body diagram forces on the shaft on the 
horizontal plane.

The reactions, RAH and RBH were determined by taking 
moment about A;
∑MA=0
1.35×340.84 
N-1.1×RBH+0.425×197.34 
N+0.325×208.58 N+0.225×173.61 N=0
1.1×RBH=1.35×340.84 
N+0.425×197.34 N+0.325×208.58 N+0.225×173.61N
RBH=650.85/1.1=591.68 N
Also, the summation of  all horizontal forces is;
∑FH=0RAH-20.74 N-26.15 N-33.52 N+RBV-35.63 N=0
RAH+RBH= 20.74 N+26.15 N+33.52 N+35.63 N
RAH+RBH=116.04  N, but, R_BH=591.68  N
RAH=(116.04 -591.68)N=475.64 N 
Downward
Based on the magnitude and location of  all horizontal 
forces acting on the shaft of  the rotating grading unit, 
the shear force and bending moment diagram on the 
horizontal plane (Figure 12) was drawn.
The resultant bending moments on the shaft were 
determined using Eqn. (51).
  Mb=√((MV )2+(MH )2                                                  (51)
=√((89.63)2+(8.91)2 =90.07 Nm



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Where: 
Mb = resultant bending moments (Nm), 
MV = maximum bending moments on a vertical plane 
((89.63) Nm), and 
MH = maximum bending moments on a horizontal plane 
(8.91 Nm)
According to Khurmi and Gupta (2005), torque on a 
shaft can be calculated using Eqn. (52).
T=(T1-T2 )×D4/2                                                      (52)
=(259.57 N-46.77N)×0.36/2=38.30 Nm 
The power required to rotate the grading cylinder shaft 
will be determined from the equation below.
PSH=2πNT/60                                                             (53)
PSH=(2π×62.5×38.30)/60=252.48 Watts
Where: PSH= power required to rotate the grading unit 
shaft (Watts)
T = torque on the shaft (Nm), 
T1 = tight side tension of  a belt (259.57  N), 
T2 = slack side tension of  a belt (46.77 N), 
D4 = diameter of  the driven pulley on the grading unit 
rotating shaft (0.36 m), and
N= rotational speed of  rotating shaft (62.95 rpm).
For a solid shaft with little or no axial load, the diameter 
of  the shaft that can withstand the applied loads can be 
determined using Eqn. (53) (ASME, 1995; Khurmi and 
Gupta, 2005).
d3=16/πτ √((Kb ×Mb )

2+(Kt×Mt )2                                   (53)   
=16/(π×45) √((1.3×90.07×1000)2+(1.2×38.30×1000)2

d3=14,236.29 mm3

d=24.24 mm
Therefore, the diameter of  the driving shaft was taken 
as 25 mm.
Where: 
d = diameter of  the shaft (mm),
Mb = bending moment (90.07Nm), 
Mt = torsional moment (38.30 Nm), and the values of  
combined shock and fatigue factor applied to bending 
moment(Kb) and combined shock and fatigue factors 
applied to the torsional moment(Kt) were taken as 1.3 
and 1.2 respectively for the gradually applied load on the 
rotating shaft and the allowable shear stress of  the shaft 

(τ) as 45 N/mm2 based on the ASME code.
The amount of  twist permissible depends on the type of  
load application and varies between 2.5 to 3.00 degrees 
per meter for line shafting. Therefore, the angle of  twist 
(for the solid shaft) can be determined using Eqn. (54) 
Khurmi and Gupta, (2005).
  θ=(T×L)/(J×G)                                                                (54)
=(38.30×1.35)/(3.8×10-8×80×109 )= 0.01685 rad or 
0.96o
The maximum twist on the shaft was found to be 
0.96o/m. The calculated angle of  twist was less than the 
permissible angle of  twist (3˚/m). So, the shaft design 
based on the torsional rigidity is safe.
Where: 
θ= torsional defl ection, or angle of  twist ( radians or 
o/m),
L = length of  the shaft (1.35 m),
Ј = polar moment of  inertia for a cross-sectional area 
about the axis of  rotation (3.8×10-8 m4),
T = torsional moment (38.30 Nm), 
G = torsional modulus rigidity (80 x 109 N/m2), and 
d = diameter of  the shaft (0.025 m).
2.3.6. Bearing selection
A bearing is a machine element that supports another 
moving machine element (known as a journal). It permits 
a relative motion between the contact surfaces of  the 
members while carrying the load (Khurmi and Gupta, 
2005). Bearing size can be selected by determining the 
maximum resultant force on it, bore size, and desire 
maximum lifespan.
R=(√(RBH

2+RBV
2 )                                                         (55)

=(√(591.68)2+(561.03)2

=0.82 kN
The design load of  a bearing can be calculated using the 
following formula (Robert et al., 2018).
Pd=VR                                                                               (72)
=1×0.82 =0.82 kN
Where: Pd= load of  the bearing (N), V= rotation factor 
1.0 if  the inner race of  the bearing rotates and 1.2 if  the 
outer race rotates, and R = radial load (N)
For a specifi ed design life in hours and a known speed 
of  rotation in rpm, the number of  design revolutions, 
L_d for the bearing would be estimated using Eqn. (56) 
(Robert et al., 2018). 
  Ld  = Hm×N×(60 min)/hr                                          (56)
=(6,000 hr)×(62.95 rpm)(60min/hr)=2.3×107 rev.
Dynamic load rate can be determined by using Eqn. (57) 
(Richard and Kelth, 2011).
  C=Pd (Ld/106 )(1/k)                                                       (57)
=0.82((2.3×10^7)/10^6 )^(1/3)  =1.08 kN 
Where: 
 C= basic dynamic load rating, 
RBH = maximum resultant force acting on a bearing at 
point B on the horizontal plane (kN),  RBV = maximum 
resultant force acting on a bearing at point B on the 
vertical plane (kN), 
R = maximum resultant reaction force on the bearings at 
point B (kN),

Figure 12: Shear force and bending moment diagram in 
the horizontal plane.



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 N = rotational speed of  the rotating the shaft (rpm), 
 Ld= the number of  design revolutions, 
Hm = according to Robert, (2018), the desired maximum 
life span of  the bearings for agricultural equipment was 
6,000 hours, and 
K= 3 for ball bearings and 10/3 for roller bearings.
Since the diameter of  the shaft has been determined to 
be 25 mm, the bearing number 205 by the bore of  25 
mm with a width of  15 mm was selected according to 
Khurmi & Gupta, (2005)(Figure 13). Consequently, the 
basic dynamic load rating of  the bearing was estimated 
using Eqn. (57) and found to be 1.08 kN. Since the basic 
dynamic load rating of  the bearing selected is less than 
the dynamic load rating by the manufacturers (i.e. 1,080N 
< 11000 N), the bearing selected was safe.

Figure 13: Isometric view and detail dimensions of  
bearing.

Estimation of  Power Required to Operate the 
Grading Machine
The power required to operate the grading machine is the 
total sum of  the power required to move the onion bulb 
inside the cylinder (PO), the power required to drive the 
grading unit (rotating cylinder) (Pc), the power required 
to overcome air resistance (PAR), and the power required 
to rotate the grading unit shaft (PSH), based on equations 
(25), (28), (29), and (53). The total power (PTO) required 
for grading and overcoming friction was determined 
using Eqn.58 (Nduka et al., 2012).
PT=PO+PC+PAR+PSH                                                         (58)
=446.35+194.30+23.08+252.48=916.21 Watts 
PTO=PT+0.10PT  (10% is possible power loss due to 
friction drive)                                                                  (59)
=916.21+0.10(916.21 )= 1007.83 Watts
= 1.35 hp
Where: 
PT = power required by the machine (Watts),
PTO= Total power required for grading machine and 
overcome loss due to friction, (watts)
PC = power required to rotate grading cylinder (Watts),
PSH= power required rotating the grading cylinder shaft 
(Watts)
PO= power required to move the onion bulb inside the 
cylinder (Watts), and
PAR = power required to over-come air resistance (Watts).
Therefore, a 3 hp Honda diesel engine with the desired 
crank speed of  1400 rpm was selected to drive the 

grading machine during the performance evaluation of  
the prototype.

Manufacturing Process of  the Machine Components 
Constructional Materials
The selection of  a proper material for a machine part or 
structural member is one of  the most important decisions 
the designer is called on. The main factors considered 
while selecting materials were the availability of  the 
materials, suitability of  the materials for the working 
conditions in service, and the cost of  the materials. 
The important properties, which determine the utility 
of  the material, are physical, chemical, and mechanical 
properties (Khurmi and Gupta, 2005).
This chapter will cover a detailed description of  the 
manufacturing process of  each machine part of  the 
grading machine Manufacturing can be defi ned in two 
ways; technologically and economically. Manufacturing 
from the technology point of  view can be defi ned as 
the application of  physical and/or chemical processes 
to alter the geometry, properties, and/or appearance 
of  a given starting material to make parts or products. 
Then these multiple parts may be assembled to make 
fi nished products. Economically manufacturing is the 
transformation of  materials into items of  greater value 
by means of  one or more processing and /or assembly 
operations, i.e. manufacturing adds value to a starting 
material by changing its shape or properties, or by 
combining it with other materials that have been similarly 
altered. The material has been made more valuable 
through the manufacturing operations performed on it 
(Groover, 2020). The step of  the manufacturing process 
helps to produce the machine locally using available 
material. Required tools and machines are used as per 
necessity. The processes to accomplish manufacturing of  
the machine involve a combination of  machinery, tools, 
power, and labor to give the fi nished part as summarized 
in Table 1below.
Machines used in the manufacturing of  the grader 
components are:

1. Lath machines
2. Welding machine
3. Bending machine
4. Manual rolling machine
5. Grinding machine
6. Hand drilling machines

Measuring, cutting, holding and other tools used:
1.Turning tool and drill bits 
2. Measuring tape and Caliper 
3. Steel rule, try square, screwdrivers
4. Grinder discs and cutter discs 
5. Metal sand paper, Scriber (pencil), and Center punch
6. Vice gripper, bench vice, and c-clamp
7. Hammer (plastic and metal), compass, and protractor
8. Paints and paint brushes.

The above parts of  an onion grading machine are those 
that can be manufactured with the tools and machines 
available at Asella Agricultural Engineering Research 



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Am. J. Food. Sci. Technol. 2(2) 1-13, 2023

Center (AAERC) workshops and tools that can be 
purchased easily from local markets. However, bearings, 
belts, and pulleys are directly purchased from the market 
based on the design requirements and dimensions.

CONCLUSION AND RECOMMENDATION
By utilizing materials found on the local market, an 
onion grading machine’s design and construction 
were completed. The machine, which has wheels for 
transporting it from one location to another, weights 
125 kg. The developed grading device had a 1488.43 kg/
hr grading capacity and a 96.04% grading effectiveness. 
By adding additional feeding mechanisms and using 
manufacturing materials appropriate for grading other 
crop types, the design can still be enhanced to increase the 
capacity and effi ciency of  a grading operation. In areas 
with access to electricity, using a variable speed motor for 
straightforward control of  the grading unit cylinder speed 
is recommended. It is advised to investigate the possibility 
of  enhancing the design and fabrication in order to put 
the product into mass production, which can also open 
up the possibility of  income generation.

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Table 1: Selected manufacturing process of  the grading machine’s main components
Serial No Grader Components Required material Required tools and activity/process
1 Handle Galvanized Iron pipe measuring, cutting, rolling, welding, grinding, 

drilling, and painting
2 Top cover Mild steel sheet metal measuring, cutting, rolling, welding, grinding, 

drilling, and painting
3 Frame Mild steel angles and 

rectangular pipe
measuring, cutting, drilling, welding, and grinding

4 Driving Shaft Mild Steel turning, facing, cutting, and milling
5 Hopper Mild steel sheet metal measuring, cutting, bending, welding, grinding, 

drilling, and painting
6 Rotating Cylinder Mild steel fl at Iron and 

round bar
measuring, cutting, rolling, welding, grinding, and 
painting

7 Outlet chutes Mild steel sheet metal measuring, cutting, bending, and welding



Pa
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