This research targets technical entrepreneurs and upcoming engineers in design of cost effective systems to support farmers improve the quality of their products.

1. 1
DESIGN AND FABRICATION OF
CEREALS WINNOWER
Jesca Ogutu and Cornelius Nganga
ABSTRACT
This project involves design, fabrication and testing of a cereals winnower.
The existing type of a cereals winnower is used by farmers to remove fine light particles from
cereals where a person either uses either wind winnowing or uses a stationary cereals winnower
which has only one sieve and the person uses a lot of effort. My cereals winnower design is
aimed at improving cereals harvesting process by making it easy to use, reducing the effort
applied by the farmers by using the reciprocating sieves, design a cereals winnower that holds a
moderate capacity of cereals and improving living standards of the cereals farmers.
The design of this winnower involves carrying out a survey and studying the existing kind of
winnowers to understand their operation.
The cereals winnower will be beneficial to the farmers by making the harvesting and grains
cleaning process easier. It will also make work easier for the farmers.
Keywords: Winnower, bending moment, mechanics of failure
INTRODUCTION
1.1 Background
Cereals Winnower
A cereal winnower is a device used to separate grains from chaff by means of a wind or current
of air.
Threshing operations leave all kinds of trash mixed with the grain; they comprise both vegetable
(e.g. foreign seeds or kernels, chaff, stalk, empty grains etc.) and mineral materials (e.g. earth,
stones, sand, metal particles etc.) and can adversely affect subsequent storage and processing
conditions. The cleaning operation aims at removing as much trash as possible from the threshed
grains.

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Traditional cleaning method is winnowing, which uses the wind to remove light elements from
the grain.
Winnowing is the natural removal of fine material from coarser sediment by wind or flowing
water, analogous to the agricultural separation of wheat from chaff. Wind winnowing is an
agricultural method developed by ancient cultures for separating grain from chaff. Wind
winnowing is used to remove weevils or other pests from stored grain. It involves throwing the
mixture (grain, seeds, husks, straw and chaff) into the air so that the wind blows away the light
chaff.
1.2 Problem Statement
Over the years it has been observed that there have been changes in the design of the cereals
winnower in various countries in the world that practice cereals farming. Currently most of the
farmers use wind winnowing.
Wind winnowing is an agricultural method developed by ancient cultures for separating grain
from chaff. It is also used to remove weevils or other pests from stored grain. Threshing, the
loosening of grain or seeds from the husks and straw is the step in the chaff-removal process that
comes before winnowing. "Winnowing the chaff" is a common expression.
In its simplest form it involves throwing the mixture into the air so that the wind blows away the
lighter chaff, while the heavier grains fall back down for recovery. Techniques used included
using a winnowing fan (a shaped basket shaken to raise the chaff) or using a tool (a winnowing
fork or shovel) on a pile of harvested grain. The limitations of using traditional ways of
winnowing like wind winnowing include;
 A lot of effort is required in the lifting of the basket containing the cereals
 The wind winnowing process highly depends on wind to blow away the light particles
and chaff, so it will be more effective on a windy day, but on a non-windy day, the wind
winnowing process is not very effective.
 Few amounts of grains can be winnowed at one instant, since a person can’t carry a large
amount of cereals, only a machine can perform winnowing of large quantities of cereals.
 Wind winnowing requires the use of both hands which is very tiresome.

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Due to the above stated limitations of traditional winnowing processes, there is a need to come
up with a cereal winnower that requires less effort in operating it, has a fan incorporated in its
design that provides the wind that blows away the light particles and has enough space that holds
a large amount of cereals to be cleaned.
1.3 Justification
Due to the need for effectiveness during cereals harvesting, there has been need to redesign the
existing cereal winnowers currently used in Kenya.
The cereals winnower is designed to tackle the three main limitations of the traditional
winnowing processes namely effort required, over dependence on the wind and the capacity of
cereals to be cleaned.
The cereals winnower is cheap, safe to use, requires less effort to operate it and is therefore of
great significance to the farming sector. The cereals winnower can be operated with only one
hand unlike wind winnowing that requires the use of both hands. The operator only needs to
rotate the handle with one hand, therefore less tiresome.
The cereal winnower will go a long way in improving the cereals farming sector in the country.
It will also help in raising the living standards of the people in the farming sector by raising
cereals harvest and hence raising quality of life in accordance to the vision 2030.
1.4 OBJECTIVES
1.4.1Main Objectives
The main objectives of the project are:
 To design an effective cereals winnower.
 To reduce the effort applied by the farmers by using the reciprocating sieves.
 To design a cereals winnower that holds a moderate capacity of cereals.
 To design a safe and cheap cereals winnower.
1.4.2Specific objectives
 To improve cereals harvesting process by simplifying the winnowing process
 To improve living standards of the cereals farmers.

4. 4
CHAPTER TWO: LITERATURE REVIEW
2.1 PAST RELATED INFORMATION
Over the years there have been changes in the design of cereals winnower. In the ancient days,
the people cleaned their cereals by wind winnowing. Over the years many other designs have
been introduced after that.
2.1.1 Wind Winnowing
Wind winnowing is an agricultural method developed by ancient cultures for separating grain
from chaff. It is also used to remove weevils or other pests from stored grain. Threshing, the
loosening of grain or seeds from the husks and straw is the step in the chaff-removal process that
comes before winnowing. "Winnowing the chaff" is a common expression.
It involves throwing the mixture of grains into the air so that the wind blows away the lighter
chaff, while the heavier grains fall back down for recovery. Techniques included using a
winnowing fan (a shaped basket shaken to raise the chaff) or using a tool (a winnowing fork or
shovel) on a pile of harvested grain.
Traditional Wind Winnowing illustration

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2.1.2 A portable winnower
A portable winnower was introduced which is a small machine that separates the straw and chaff
from the grain in a similar manner to the combined harvester.
Advantages of using a portable winnower are;
 A portable winnower is a small machine and its cheap
 A portable winnower is used for cleaning the chaff from the grain
 Since it’s a stationary machine breakages are low and it can be shared or hired without an
operator.
CHAPTER THREE: THEORY
3.0 THEORY OF MY STUDY
The process used to collect information and data for the purpose of making decisions.
Information about the project was found through the following means:
Internet
Textbooks
Interviewing the farmers
Observing the farmers harvest and clean the cereals
Literature Review
Extensive literature review is required on the existing winnowing methods currently used. This
involved the use of the library resources and the internet. Several visits to the cereals farming
areas helped to acquaint one with the existing winnowing methods currently used.
Parts of cereals winnower
1) Fan and its housing
2) Metallic stand (rectangular in shape)
3) Pulley system
4) Combination of the three sieves (wire mesh)
5) Offset-crank mechanism

6. 6
Components
1) Shafts (two)
2) Bearings (four)
3) Pulleys (two)
4) V-belt
5) Fan and its housing
6) 3 sieves (different openings-large, medium and small)
7) Slider-crank mechanism
8) Handle
9) Frame
Mechanical fans
A mechanical fan is a machine used to create flow within a fluid, typically a gas such as air.
The fan consists of a rotating arrangement of vanes or blades which act on the air. The rotating
assembly of blades and hub is known as an impeller, a rotor, or a runner. Usually, it is contained
within some form of housing or case. This may direct the airflow or increase safety by
preventing objects from contacting the fan blades. Most fans are powered by electric motors, but
other sources of power may be used, including hydraulic motors and internal combustion
engines.
The wheel is like a paddle wheel with or without side rims. The blades are perpendicular to the
direction of the wheel rotation and the fan runs at a relatively medium speed to move a given
amount of air.
Forces acting on a propeller
Five forces act on the blades of an aircraft propeller in motion, they are:
1) Thrust bending force
Thrust loads on the blades act to bend them forward.
2) Centrifugal twisting force
Acts to twist the blades to a low or fine pitch angle.
3) Centrifugal force
The force felt by the blades acting to pull them away from the hub when turning.

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4) Torque bending force
Air resistance acting against the blades, combined with inertial effects causes propeller blades to
bend away from the direction of rotation.
The propeller’s efficiency is determined by
The blade efficiency is in the ratio between thrust and torque:
Offset-crank mechanism causing reciprocating motion
Reciprocating motion, also called reciprocation, is a repetitive up-and-down or back-and-forth
linear motion. It is found in a wide range of mechanisms, including reciprocating engines and
pumps. The two opposite motions that comprise a single reciprocation cycle are called strokes.
A crank can be used to convert circular motion into reciprocating motion, or conversely turn
reciprocating motion into circular motion.
The continuing rotation of the rotating circular disk drives the metallic rod connected to the sieve
combination to and fro, ready for the next cycle. The sieve combination moves in a reciprocating
motion, where the rotation motion of the circular disk is converted into linear motion of the sieve
combination.
Reciprocating motion is close to, but different from, sinusoidalsimple harmonic motion. The
point on the rotating circular disk which connects the connecting rod rotates smoothly at a
constant velocity in a circle. Thus, the horizontal displacement, of that point, is indeed exactly
sinusoidal by definition. However, during the cycle, the angle of the connecting rod changes
continuously. So, the horizontal displacement of the "far" end of the connecting rod (i.e.,
connected to the sieve combination) differs from sinusoidal.

8. 8
To get the torque used the following formula
Torque=F*r*sin α
One revolution of the crank causes the (mass) sieve combination to complete one reciprocating
motion i.e. back and forth.
Belt Drives
The belts are used to transmit power from one shaft to another by means of pulleys which rotate
at the same speed or at different speeds. The amount of power transmitted depends upon the
following factors:
1) The velocity of the belt.
2) The tension under which the belt is placed on the pulleys.
3) The arc of contact between the belt and the smaller pulley.
4) The conditions under which the belt is used.
It may be noted that
1) The shafts should be properly in line to insure uniform tension across the belt section.
2) The pulleys should not be too close together, in order that the arc of contact on the
smaller pulley may be as large as possible.
3) The pulleys should not be so far apart as to cause the belt to weigh heavily on the shafts,
thus increasing the friction load on the bearings.
4) A long belt tends to swing from side to side, causing the belt to run out of the pulleys,
which in turn develops crooked spots in the belt.

9. 9
Selection of a Belt Drive
The following are the various important factors upon which the selection of a belt drive depends:
 Speed of the driving and driven shafts
 Speed reduction ratio
 Power to be transmitted
 Centre distance between the shafts
 Shafts layout
 Space available
Types of Belts
1) Flat belt
2)V-belt- The V-belt is mostly used in the factories and workshops, where a moderate amount of
power is to be transmitted, from one pulley to another, when the two pulleys are very near to
each other. In this case, the v-belt is used.
3) Circular belt
Open belt drive.
The open belt drive is used with shafts arranged parallel and rotating in the same direction. In
this case, the driver pulley A pulls the belt from one side (i.e. lower side) and delivers it to the
other side (i.e. upper side). Thus the tension in the lower side belt will be more than that in the
upper side belt. The lower side belt (because of more tension) is known as tight side whereas the
upper side belt (because of less tension) is known as slack side. The length of the open belt drive
is given by
Power transmitted by a belt
Let P = Power
T1 and T2 = tension of tight side and tension of slack side
r1 and r2=radius of driver and radius of follower
v=velocity
𝑃 = (𝑇1 − 𝑇2) × 𝑣

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The torque exerted on the driving pulley i.e. driver is (𝑇1 − 𝑇2)𝑟1.
The torque exerted on the driven pulley i.e. follower is (T1 – T2) r2.
Velocity Ratio of Belt Drive
It is the ratio between the velocities of the driver and the follower or driven. It may be expressed,
mathematically, as discussed below:
Let d1 = Diameter of the driver
d2 = Diameter of the follower
N1 = Speed of the driver in r.p.m
N2 = Speed of the follower in r.p.m
∴ Length of the belt that passes over the driver, in one minute
= π d1.N1
𝜋 × 0.15 × 100 = 47.12
∴ The length of the belt that passes over the driven, in one minute
= 𝜋 d1. N1
𝜋 × 0.1 × 150 = 47.12
Since the length of belt that passes over the driver in one minute is equal to the length of belt that
passes over the follower in one minute, therefore
πd1 . N1 = π d2. N2
Advantages and Disadvantages of V-belt Drive over Flat Belt Drive
Advantages
1) The V-belt drive gives compactness due to the small distance between the centers of pulleys.
2) The drive is positive, because the slip between the belt and the pulley groove is negligible.
3) The drive is smooth.
4) It provides longer life, 3 to 5 years.
5) It can be easily installed and removed.

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6) The operation of the belt and pulley is quiet.
7) The belts have the ability to cushion the shock when machines are started.
8) The high velocity ratio (maximum 10) may be obtained.
Disadvantages
1) The V-belt drive cannot be used with large center distances.
2) The V-belts are not as durable as flat belts.
3) The construction of pulleys for V-belts is more complicated than pulleys for flat belts.
4) Since the V-belts are subjected to certain amount of creep, therefore these are not suitable for
constant speed application such as synchronous machines, and timing devices.
5) The belt life is greatly influenced with temperature changes, improper belt tension and
mismatching of belt lengths.
Material used for Belts
The material used for belts and ropes must be strong, flexible, and durable. It must have a high
coefficient of friction. In this case rubber was used to make the v-belt.
Lubrication process
-The contacting surfaces in rolling bearings have a relative motion that is both rolling and
sliding, and so it is difficult to understand exactly what happens. If the relative velocity of the
sliding surfaces is high enough, then the lubricant action is hydrodynamic. Elastohydrodynamic
lubrication(EHD) is the phenomenon that occurs when a lubricant is introduced between surfaces
that are in pure rolling contact. When a lubricant is trapped between two surfaces in rolling
contact, a tremendous increase in the pressure within the lubricant film occurs. But viscosity is
exponentially related to pressure, and so a very large increase in viscosity occurs in the lubricant
that is trapped between the surfaces.
-The purposes of an antifriction-bearing lubricant may be summarized as follows:
1. To provide a film of lubricant between the sliding and rolling surfaces
2. To help distribute and dissipate heat
3. To prevent corrosion of the bearing surfaces
4. To protect the parts from the entrance of foreign matter
Either oil or grease may be employed as a lubricant

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Bearings
A bearing is a device that constrains relative motion between moving parts to only the desired
motion. A bearing is a device that is used to enable rotational or linear movement, while
reducing friction and handling stress.
Ball bearings
A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation
between the bearingraces. The purpose of a ball bearing is to reduce rotational friction and
support radial and axial loads. It achieves this by using at least two races to contain the balls and
transmit the loads through the balls. Because the balls are rolling they have a much lower
coefficient of friction than if two flat surfaces were sliding against each other. Ball bearings are
commonly used because they can handle both radial and thrust loads.
CHAPTER FOUR: METHODOLOGY
4.1 MATERIALS & EQUIPMENT
Materials Yield Strength
(MPa)
Ultimate Strength
(MPa)
Density (g/cm3
)
Mild Steel (rods and
metal bars)
250 400-550 7.8
Aluminium sheet
metal
241 300 2.7
Galvanized iron sheet
metal
3 7.874
Wood 40
Rubber 16
4.1.1 Tools used
 Hammer
 Tinsnips
 Hacksaw
 Scriber

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 Tape measure
 Chisel and mallet
 Rough and smooth file
 Vernier calipers
 Screw driver
 Steel rule
 Divider
 Center punch
4.1.2 The machines used are:
 Lathe machine
 Power saw
 Welding machine
 Grinding machine
 Drilling machine
 Rolling machine
 Shearing machine
 Bending Machine
4.2 DESIGN WORK
4.2.1 Shafts and pulleys
For a system with two shafts and two pulleys.
D1n1=D2n2
Where
D1=driving pulley diameter
n1= revolutions of the driving pulley
D2= driven pulley diameter
n2= revolutions of the driven pulley

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The revolution of driven pulley
𝑛2 = (𝑑1 𝑛1)/𝑑2
The revolution of driven pulley
𝑛1 = (𝑑2 𝑛2)/𝑑1
The diameter of driven pulley
𝑑2 = (𝑑1 𝑛1)/𝑛2
Diameter of driver pulley
𝑑1 = (𝑑2 𝑛2)/𝑛1
4.2.2 Design of the shaft
There are two shafts required:
 That which connects the hand lever and the driving pulley
 That which the fan blades are mounted on and is connected to the driven pulley
Shaft transmitting power from hand lever to driving pulley.
Taking the force applied on the hand lever to be 50N
Height of the hand lever is 15cm
Revolutions made per minute are 100
The power transmitted by the shaft in watts is given by:
𝑷 =
𝟐𝝅𝑵𝑻
𝟔𝟎
= 𝑻 . 𝝎
𝝎 =
𝟐𝝅𝑵
𝟔𝟎
Torque, T = force * radius
= 50𝑁 × 0.15𝑚
= 7.5 N-m
Therefore,𝑷 =
𝟐𝝅×𝟏𝟎𝟎×𝟕.𝟓
𝟔𝟎

15. 15
P = 78.5 watts
The Length of the shaft = 60 cm
The Radius of the shaft = 1cm
For the shaft on which the fan blades are mounted
Length of the shaft = 50cm
Radius of the shaft = 1cm
Power transmitted to the shaft by the driven pulley:
𝑁1
𝑁2
=
𝐷2
𝐷1
Diameter of the driving pulley, D1 = 15cm
Diameter of the driven pulley, D2 = 10cm
N1 = 100 r.p.m.
N2 =100 ×
15
10
= 150 r.p.m
4.2.3 Length of an open belt drive
The open belt drive is illustrated in Figure. Assume O1 and O2 are the pulley centers and AB and
CD are the common tangents on the circles demonstrating the two pulleys. The entirety length of
the belt 'L' is given by following
L = AB + Arc BHD + DC + Arc CGA
Assume r be the radius of the smaller pulley,
R be the radius of the larger pulley,
C be the centre distance among the pulleys, and
β be the angle subtended through the tangents AB and CD with O1 O2.

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Draw O1 N parallel to CD to meet O2 D at N.
By geometry, ∠ O2 O1, N = ∠ C O1 J = ∠ D O2 K= β
Arc BHD = (π + 2β) R,
Arc CGA = (π + 2β) r
AB = CD = O1 N = O1 O2cos β = C cos β
sin β= R - r/ C
or,
β= sin -1
(R - r )/ C
For small value of β;
β= (R - r )/C
It provides approximate length.
4.2.4 Offset crank mechanism
F=147.15N

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R=0.12m
𝛼 = 30°
Torque=F*r*sin α
Let 𝐹 = 𝑚𝑔
= 15 × 9.81 = 147.15𝑁
Torque = 15 × 9.81 × 0.12 × sin 30° = 8.829𝑁𝑚
4.2.5 Weld joints
A weld joint is a permanent joint obtained by fusion of the edges of the two parts to be joined
together, with or without the application of pressure and a filler material. Welding is extensively
used in fabrication as an alternative method for casting and as a replacement for bolted or riveted
joints.
Advantages of Welded Joints
1. The welded structures are usually lighter than riveted structures
2. Modifications and additions can be easily made in the existing structures.
3. The welded structure is smooth in structure.
4. In welded connections, the tension members are not weakened as in the case of riveted
joints.
5. A welded joint has the strength of the parent metal itself.
6. Welding process is shorter than riveting process
MIG welding will be used in this design. MIG welding is a semi-automatic process that uses a
continuous wire feed as an insert or semi-inert gas mixture to protect the weld from
contamination.
Several types of welded joints exist, these include the following;
 Lap joint or the fillet joint. The lap joint is obtained by overlapping the plates and then
welding the edges of the plates. The cross-section of the fillet is approximately triangular.

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It is further categorized into single transverse fillet, double transverse fillet and parallel
fillet joint.
 Butt joint. It is obtained by placing the plates edge to edge.
It is further categorized into;
 Square butt joint
 Single or double V-butt joint
 Single or double U-butt joint
In this design double transverse fillet joint will be used
Strength of transverse fillet welded joints
In order to determine the strength of the fillet joint, it is assumed that the section of fillet is a
right angled equal two side’s triangle.
The minimum area of the weld is obtained at the throat, which is given by the product of the
throat thickness and length of the weld.
Minimum area of the weld or throat area A is given by
A=0.707s x l
If Ϭt is the allowable tensile stress for the weld metal, then the tensile strength of the joint for
double fillet weld is given by
P=2×0.707×S×Ϭt×l=1.414×S×Ϭt×l
12.384 × 103
= 1.414 × 𝑆 × 0.3 × 13.76 × 106
S= 0.0021
4.2.6 Bolted joints
Bolted joints loaded in shear are treated exactly alike in design andanalysis.
The bending moment is approximately M = Ft/2, where F is the shearing force and
tis the grip of the rivet, that is, the total thickness of the connected parts. The bending stress in
the members or in the rivet is, neglecting stress concentration,
σ =
M
I/c

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Where I/c is the section modulus for the weakest member or for the rivet or rivets, depending
upon which stress is to be found. The calculation of the bending stress inthis manner is an
assumption, because we do not know exactly how the load is distributed to the rivet or the
relative deformations of the rivet and the members. Although this equation can be used to
determine the bending stress, it is seldom used in design; instead its effect is compensated for by
an increase in the factor of safety.
The stress in the bolt is
𝝉 =
𝑭
𝑨
Where A is the cross-sectional area of all the bolts in the group and F is the force exerted.
4.3 FABRICATION OF PARTS
Fan and its housing
It is made using mild steel sheet metal. Four pieces are cut and welded together to the shaft that
is connected to the driven pulley. The fan housing is made from mild steel sheet metal that is
first cut, rolled using a sheet metal rolling machine then welding the parts together to form the
fan casing.
Metallic stand
The metal stand is made from mild steel metal bars and it is for supporting the other parts of the
cereals winnower. The mild steel metal bars are cut according to the required measurements and
then welded together. The four metal stands have a length of 80cm and 4cm thick. Two of the
side frames are 90cm in length and 4cm thick while the other two side frames have a length of
45cm and 4cm thick.
Pulley system
The pulley system is made of two pulleys and a v-belt. The diving pulley has a diameter of 15cm
while the driven pulley has a diameter of 10cm.
Slider-crank mechanism
The slider-crank mechanism is a particular four-bar linkage configuration that converts linear
motion to rotational, or vice versa.
With an offset slider-crank mechanism, an offset distance is introduced. This offset distance is
referred to as L1 and is the fixed distance between the crank arm pivot point and the slider axis.
This offset distance means that the slider-crank motion is no longer symmetrical about the
sliding axis. In addition, the required crank angles of the forward and reverse strokes are no

20. 20
longer equivalent. An offset slider-crank provides a quick return when a slower working stroke is
desired.
With offset slider-cranks, the stroke is always twice the crank length, and as the offset distance
increases, the stroke also becomes larger. The potential range for the offset distance can be
written in relation to the other mechanism lengths, L2and L3, as the equation
L1< L3 - L2
The design of an in-line crank slider mechanism involves finding the two link lengths, L2and L3,
and an appropriate offset distance, L1, in order to achieve the wanted stroke,(ΔR4)max, and
imbalance angle, β.
It’s ma de up of two rods connected together with a bolt and nut. One rod is welded to the
combination of the three sieves. The other rod is connected to the circular disk connected to the
shaft with the driving pulley. The circular disk is connected to the other rod with a bolt and nut.
As the driving shaft is rotated, the circular disk rotates, causing the connecting rod to rotate with
it. In the end the connecting rod connected to the combination of sieves moves in a reciprocating
motion.
Combination of the three sieves (wire mesh)
There are three types of sieves (wire mesh) used. The sieves are connected using rectangular
wood support. The sieves frame has length of 44.5cm, width of 44.5cm and a height of 6cm and
1.5cm thick.
4.5 PROCESSES TO BE EMPLOYED IN THE FABRICATION PROCESS
The fabrication of the cereal winnower is to be done according to the design specifications. To
come up with a complete cereal winnower, various different types of machines and machine
technology are required. The list below includes some of the processes that are to be employed in
the fabrication process:
 Machining
 Welding
 Metal forming and folding
 Riveting
 Metal cutting
4.5.1 Machining
Machining is a process of giving a work piece a new configuration by cutting or shaping.
Typically performed on a machine tool or machining center. It includes cutting and shaping of all
kinds of materials.

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Machining processes in this project include: drilling, boring, grinding, facing.
Turning
Is a machining operation in which a work piece is rotated while a cutting tool removes material.
A work piece is held in a chuck, mounted on a face and rotated while a cutting tool is fed into it
along its periphery of across its end or face.
Grinding
Grinding is a machining operation in which material is removed by a powered abrasive wheel,
stone, belt, paste, and sheet, compound. Is a technique where a rough surface is grinded into a
soft layer that is less dangerous to work with. It is also used to realize fine finish tolerance and
surface finishes.
Facing
Is an operation that provides a true reference before beginning another operation.
Cutting and bending: this involves use of force to completely change the shape of the work
piece in the case of bending. In this project, the barrel is to be cut and bent from a metal sheet to
assume a cylindrical profile. The nozzle is to be cut and bent to appropriate shape from a metal
sheet.
Fitting: this involves marking out, bending, cutting, riveting of sheet metal, for example in the
fabrication of the barrel, the nozzle and the fire pot.
4.5.2 Welding
It is a method of joining different materials especially metals. Filler material may be used or the
joint get formed due to pool of melt at the base metal or mixing with the left metal. Welding may
use heating technique. Welding can be classified into major categories namely:
 Gas welding e.g. oxyacetylene
 Arc welding e.g. MIG and TIG
 Resistance welding
 Thermo chemical welding
 Radiant energy welding
Welding joints is preferred over other joining methods due to the following qualities. Such
material qualities are:

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 Strong on the base metal
 Permit freedom in design
 Large number of material alloy can be joined
 Welding can be mechanized and automatable.
 However welding has the following disadvantages
 Harmful radiations
 Residual stress develops in material
In this design project am going to use arc welding in joining of the barrel to its base and also
come up with the nozzle profile.
4.5.3 Metal cutting
Is any machining process used to part metal or a material or give a work piece a new
configuration.
4.5.4 Metal forming and folding
This is a process that involves manipulation of the work piece to intentionally change its shape
and profile. Sheet of BMS steel to required dimensions before undergoing some metal folding
into a cylindrical profile is to be used as the fire pot. A sheet of stainless steel is to be cut and
folded to required shape for welding.
4.5.5 Riveting
The function of riveting is to make a connection that has strength and tightness. The tightness is
necessary to contribute to the strength and to prevent leakages. In this project, riveting is to be
used for making the fan housing since it is made of galvanized iron that cannot be welded. The
fan housing is riveted so that the housing covers part of the fan (i.e. 225°)
Lubrication
-The contacting surfaces in rolling bearings have a relative motion that is both rolling and
sliding, and so it is difficult to understand exactly what happens. The purposes of an antifriction-
bearing lubricant may be summarized as follows:
1. To provide a film of lubricant between the sliding and rolling surfaces
2. To help distribute and dissipate heat
3. To prevent corrosion of the bearing surfaces
4. To protect the parts from the entrance of foreign matter

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Either oil or grease may be employed as a lubricant.
ASSEMBLY
After fabrication all of the parts are assembled to form one unit.
-The frame is welded together to form a rectangular frame
-Four rectangular pieces are cut and filled to obtain smooth surfaces
-Each piece is drill a circle with a diameter of 20mm
-The pieces are welded to the frame
-Two shafts of 20mm diameter are machined and fitted through the drilled holes
-Three sieves are made with different spacing (large, medium and small)
-The frame is made of wood with a square shape
-The sieves or mesh are attached to the frames
-The frames are connected together with four square connecting rods with the length of 420mm
-The four square rods are drilled bores of 4mm diameter at the intervals of 140mm
-Screws are used to attach the three sieve frame with the four square rods.
-Two pulleys are made one with a diameter of 150 mm and the other with a diameter of 100mm,
one act as a driving pulley and the other is the driven pulley
-The two pulleys are drilled bores of 20mm at the centers and fitted onto the two shafts
-A v-belt is connected to the two pulleys
-Four blades are sharpened and welded to the lower shaft at 90º to each other
-The fan housing is welded to the frame to cover up the blades
-A slider-crank mechanism is connected, one rod is welded to the combination of sieves and the
circular plate is welded to the upper shaft. The rod and the circular are connected by another rod
using bolts and nuts.
-Oil and grease are used to lubricate the moving parts of the cereal winnower like the bearings.
-After assembling all parts, the cereal winnower is painted.

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Testing
Various components of the cereal winnower are tested individually before testing the final
assembly. The offset-crank mechanism is tested to see if the rotary motion is efficiently
converted to linear motion. The bearings are tested to see if they rotate well without obstacle that
is if the lubricant was efficient. The handle is rotated to check if both pulleys and shafts rotate.
Their rotation causes the rotation of the fan and the reciprocation motion of the sieves.
CHAPTER FIVE: RESULTS AND DISCUSSION
5.1 Performance of my model
After assembling all components the cereals winnower was operational. As the handle was
rotated ,the circular disk (crank) rotated causing the connecting rod to rotate as the lower
connecting rod was caused to move to and fro (reciprocating motion). At the same time the lower
pulley enabled the lower shaft to rotate causing the fan also to rotate.
One complete revolution of the handle caused the sieve combination to complete one
reciprocating motion i.e. to and fro.
The crank speed of rotation is the same as the handle speed of rotation.
The pulley system worked efficiently meaning the pulleys drove the two shafts connected to
them well. The bearings performance was good due to sufficient lubrication. The metal frame
was strong enough to support the other mechanisms and parts joined to it. The fan rotated well
and the fan housing helped in directing air to the sieve combination.
The problem was at the offset crank mechanism. The lower connecting rod was place too low
making the reciprocating motion difficult to accomplish.
The mechanism used to connect the sieve combination to the metallic frame experienced a lot of
friction because of the metal surfaces in contact which hindered the smooth reciprocating motion
anticipated
5.2 Economic analysis
The economic analysis is done to compare the costs with benefits and to determine if the project
has an acceptable return. The project will only cost Ksh. 14,000 which is acceptable because the
benefits are good. The benefits include winnowing acceptable capacity levels of the grains, the
farmers using less effort to operate the winnower and the winnowing process will take shorter

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duration compared to the time required for wind winnowing. The cereals winnower is long
lasting since the components are made from long lasting materials. It is not expensive to
maintain as it require only frequent lubrication and replacement of v-belt when it wears off
replacement of bearing when damaged.
CHAPTER SIX: CONCLUSION AND RECCOMMENDATION
6.1 Conclusion
The project has been successful despite some few challenges. The production of the offset crank
mechanism was successful, with minimal variation from the original design required. Specified
tolerances of interfacing parts were met and functioned as intended. Assembly was conducted
through a procedure that allowed for incremental adjustments, minimizing system friction.
Satisfactory operation of the cereals winnower was achieved with minimal tuning. The movable
parts moved properly because the lubrication was effective.
Challenges
The challenges faced were:
1) Inadequacy of funds for sustaining the project
2) Unavailability of required materials e.g. bearings, metallic pulleys
3) Deviations from the required accurate measurements due to welding which caused
increase in length of the work pieces
4) Long queues on machines resulting to delays
5) Machine failures during operation leading to manual operation which is cumbersome
6.2 Recommendations
The mechanical and manufacturing department should do the following
1) Provide the students with more raw materials required for the fabrication process.
2) Provide enough machines to avoid queuing for long periods during the fabrication process
3) Provide enough funding for the project
Recommendations of my study
1) Use pulleys made from metal to ensure the pulleys and the shafts don’t rotate separately.

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2) Use rollers between the sieve combination rods and the metallic frame to make the
reciprocation motion easily attainable. This will reduce friction between the metallic surface
contacts.
3) Use an inline slider crank mechanism which will eliminate difficulties in rotating the crank for
complete revolutions (360°)
REFERENCES
[1] R.S Khurmi, J.K Gupta, Machine Design,2005, First Multi Colour Edition,
Eeurasia Publishing House(PVT) Ltd, New Delhi.
[2] Budynas and Nisbett(2008)”Shigley’s Mechanical Engineering Design”.
United States: the McGraw-Hill Companies, Inc.
[3] Norton, Robort L. Machine Design: An Integrated Approach, 2/E. Pearson
Education India, 2000.
[4]The Winnower. (1973). Eindhoven [the Netherlands: TechnischeHogeschool
Eindhoven.
[5]Bleier, F. P. (1998). Fan handbook: Selection, application, and design. New
York: McGraw-Hill.
[6]Vinogradov, O. (2000). Fundamentals of kinematics and dynamics of machines
and mechanisms. Boca Raton: CRC Press.
[7]Myszka, D. H. (2002). Machines and mechanisms: Applied kinematic analysis.
Upper Saddle River, NJ: Prentice Hall.