PROJECT

ON

DESIGN AND DEVELOPMENT OF POTTER’S WHEELFor their Partial Fulfillment of the Award of B. Tech (Hons.) degree

Under the guidance

Of

Prof. Shalendra Kumar,

Dept. of Mechanical Engineering

By

Pawan Kothiwal 129/05

Vasanth 147/05

Rajesh Kumar 155/05

Raj Kumar Poddar 156/05

Ramanath Singh 162/05

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ACKNOWLEDGEMENT

We would like to thank our guide Prof. Shalendra Kumar, Department of Mechanical Engineering, NIT Jamshedpur whose loving attention and care made this project what it is now.

We would also like to thank everyone who has been directly or indirectly involved with creation of this project.

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CONTENTS

S. NO. TITLE PAGE NO.

1. INTRODUCTION 5

2. HISTORY 7

3. TECHNIQUES OF THROWING 9

4. DOWN THE AGES 10

5. NEED FOR MODIFICATIONS 14

6. AIM OF OUR PROJECT 15

7. BEARINGS 16

8. BEVEL GEARS 18

9. CHAIN SPROCKET DRIVE 20

10. SHAFT 23

11. CATIA DESIGN OF MODIFIED POTTER’S WHEEL

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12. ADVANTAGES AND DISADVANTAGES

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13. BIBLIOGRAPHY 27

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INTRODUCTION

In pottery, a potter's wheel is a device used in the shaping of round ceramic wares. The wheel may also be used during the process of trimming excess body from dried wares and for applying incised decoration or rings of colour. Use of the potter's wheel became widespread throughout the Old World, but was unknown in the Pre-Columbian New World, where pottery was hand-made by methods that included coiling and beating.

The potter's wheel may occasionally be referred to as a "potter's lathe". However the term is better used for another design of machine that is used for a different shaping process, turning, similar to that used for the shaping of metal and wood articles.

The techniques of jiggering and jolleying can be seen to be an extension of the Potters wheel: in jiggering a shaped tool is slowly brought down onto plastic clay body that has been placed on top of a rotating plaster mould. The jigger tool shapes one face whilst the mould the other. The term is specific to shaping of flatware, plates, whilst a similar technique, jolleying, refers to the production of holloware like cups.

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HISTORY

It was known that many early ceramics were hand-built using a simple coiling technique in which clay body was rolled into long threads that were then pinched and beaten together to form the body of a vessel. In the coiling method of construction, all of the energy required to form the main part of a piece is supplied indirectly by the hands of the potter. This changed with the introduction of the fast-wheel, early forms of which utilized energy stored in the rotating mass of the heavy stone wheel itself. The wheel was wound-up and charged with energy by pushing it round with a pencil, an arrangement that permitted the energy stored in the wheel to be finely directed to where it was not really required, at the point where the hands of the potter come into contact with the clay hulk. Unlike hand-building, in wheel-throwing the bulk of the energy used comes directly from the hands of the potter. The introduction of the fast-wheel brought benefits in the form of speed and a job that might have taken hours, or even weeks, to complete was reduced to one that could be done in minutes.

Early ceramics built by coiling were often placed on mats or large leaves to allow them to be worked more conveniently. This arrangement allowed the potter to turn the vessel under construction, rather than walk around it to add threads of clay body and it has been proposed that the earliest forms of the potter's wheel were developed as an extension to this procedure. The earliest versions of the wheel were probably turned slowly by hand or by foot while coiling a pot, but later developments allowed energy stored in a flywheel to be used to speed up the process of throwing.

It is not known when the potter's wheel first came into use, but dates between about 8,000 BC to about 1,400 BC have been suggested. Many modern scholars suggest that it was first developed in Mesopotamia, although Egypt and China have also been claimed as possible places of origin. A stone potter's wheel found at the Mesopotamian city of Ur in modern-day Iraq has been dated to about 3,129 BC, but fragments of wheel-thrown pottery of an even earlier date have been recovered in the same area. By the time of the early civilizations of the stone Age the use of the potter's wheel had become widespread. Pottery could now be made in greater numbers with the aid of a machine, a first step towards world industrialization.

In the Iron Age the potter's wheel in common use had a turning platform about a meter above the floor, connected by a long axle to a heavy flywheel at ground level. This arrangement allowed the potter to keep the turning-wheel rotating by kicking the flywheel with the foot, leaving both hands free for manipulating the vessel under construction. However, from an ergonomic standpoint, sweeping the foot from side to side against the spinning hub is rather awkward. At some point, an alternative solution was invented which involved a crankshaft with a lever, that converts up and down motion into rotary motion. Sewing machines such as those pioneered by the Singer Corporation have manual models operated by this method.

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The use of the motor-driven wheel has become common in modern times, particularly with craft potters and educational institutions, although human-powered ones are still in use and are much preferred by some studio potters.

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Techniques of throwing

There are many techniques in use for throwing ceramic containers, although this is a typical procedure:

A round, moist lump of clay body is thrown down onto the wheel head or a bat (sometimes called a "batter board") attached to it. The lump is made even and forced to the centre of the wheel by applying pressure with the hands. The thrower finds the center of the clay by moving a thumb across the lump until no more friction is felt. The thumb is pressed into the center of the lump, stopping about 5 mm from the wheel head. The hole thus made is widened. The sides thus defined are pulled up and made thinner by pressure between the hands. The vessel is shaped and the mouth is smoothed. The vessel is cut from the wheel head with a cheese wire and left to stiffen. Sometimes the stiffened vessel is inverted on the wheel and trimmed a sharp tool.

A skilled potter can quickly throw a vessel from 15 kg clay. Alternatively, by throwing and adding coils of clay then throwing again, pots up to four feet high may be made, the heat of a blowlamp being used to firm each thrown section before adding the next coil. In Chinese manufacture, very large pots are made by two throwers working simultaneously.

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Potter’s wheel down the ages

Sumerian potter's wheel -the story probably begins in the Middle East around 4000 BC (6000 BP). The village settlements were growing in size and prosperity. A new phase in man's development was happening. In what is today southern Iraq, or Ancient Mesopotamia, the first urban civilization was being created; villages grew into towns and then towns into the great city states: Ur, Uruk, Ubaid, Eridu, Lagash etc. By 3000 BC. The people of these cities, the Sumerians, had already established a sophisticated trading commercial culture. This was the first town and city based civilization on this planet. New crafts and occupations evolved. More skills and tools were invented.

The Effects of Specializing

To a great extent all was triggered as a result of increased division of labour and job specialization within earlier small communities. Of course some men still hunted and fished, but others now planted crops and reared animals and, as they became more experienced, farming methods improved, and food production increased and so did the population. Trade expanded over the whole region. More pots were needed and various ways were tried to speed up all the pottery techniques: making, decorating and firing.

Who did what - Men or Women?

Most of these changes affected the work and life style of the men much more than their womenfolk. Most women were already almost fully occupied and "specializing" in the vital task of bearing and rearing children. Any other tasks done by the women must therefore have been part-time and close to the home. Women almost certainly developed the techniques of sewing, weaving and basket making in most prehistoric communities. They were probably also the first real potters - the makers of bowls, dishes, jugs etc. so it is not surprising that in these early village societies building a basket and coiling a pot had a lot in common.

Coiling Pots

The ancient technique of building a coiled pot involves squeezing, squashing and smoothing the successive layers of coils into a thin even wall which swells or tapers as it grows and encloses a shape. To do this you need to turn the pot around slowly as you work.

Early potters soon learned to make the task of periodically turning the pot much easier and more efficient by beginning their coiling on a dish or bowl, or even a flat plate or smooth platter they could twist round as they worked.

Most early coiled pots are round bottomed. They were probably started in a bowl which could be easily turned or rolled around whilst adding and smoothing the clay coils.

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Other coiled pots taper downwards to a small base. This would make the pots easier to turn whilst coiling.

The base was probably started by pressing a lump of soft clay or a spiral of coils into a shallow round bottomed bowl and smoothing it out with the fingers or a piece of wood or a bone rib. Coils were then added progressively. The shallow bowl gave support to the soft clay as first coils were added. The rounded bottom made it easy to pull the pot around bit by bit. As the base and lower coils gradually dried and hardened progressively they gave firmer support to the soft coils being added above.

In more remote regions of the world women are probably still coiling pots in this way. These illustrations show these methods still being used within the last century in some African villages.

Squatting down with the bowl between the legs. It is easy to turn such a bowl as each coil is added and squeezed and smoothed into the wall.

Making a round base. A pancake of clay about to be pressed into a fired clay bowl. Sausage-like coils in the foreground.

Adding and squeezing a coil as the wall is built.

Adding small coils at the neck of the pot. Ready to build out the rim.

Thinning and opening to make a rim.

Drying the pots.

Finished pots have been allowed to dry completely in the sun, piled up in a heap on brushwood and bundles of dried grass.

An open bonfire of the finished pots.

More brushwood piled around the dried pile of pots, the bonfire lighted and then fed with more bundles of dry grass.

Platters and bowls for faster coiling.

Innumerable ways developed of using a platter or bowl to speed up coiling. Here is an example found in the Indian subcontinent. However, soon after 4000 BC. In Mesopotamia a new discovery/invention was being exploited...

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The Arrival of the Wheel

The principle of the Wheel was discovered earliest in southern Iraq(Mesopotamia).

By discovering the principle of the wheel, the Sumerians were able to give up pulling provisions or people along on sledges or dragging heavy objects over a series of logs. They devised how to construct the first carts and chariots.

This strange wedge shaped object c. 3000 BC. was found in an ancient Sumerian royal grave at Ur in Iraq. (It may have been a sounding box for a harp). It includes perhaps the earliest drawings of wheeled carts or chariots. The whole surface is covered with a decoration made up of tiny carved pieces of lapis, ivory and limestone stuck together on the wooden box with bitumen; a sort of mosaic with engraved drawing. There are two main rectangular panels illustrating a great battle and then the plunder and celebration.

This is a detail from the Battle scene: Warriors in a horse drawn cart or chariot. This new weapon of war has four wooden wheels made out of two semicircular pieces bolted together. It must have been a deadly weapon at the time. Soon potters and other craftsmen found more peaceful uses for the wheel...

Faster Coiling on a Turntable...

Eventually a small turntable or "tournette" was developed. With this a pot could be turned around much more easily and quickly. The pot making technique in Mesopotamia now gradually gradually changed

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during the third millennium BC as the more potters adopted the turntable for making and decorating. However, it took a long time for free running steady turntables to be developed, therefore "throwing", as we understand the technique today, did not develop for a long time to come. It would be more accurate to describe this turntable making process as "fast coiling".

And Men Became The Potters...

Until the arrival of the wheel, the women usually made the pots - by coiling. With so many other responsibilities they could only be part-time potters. With the invention of the wheel, men appear to take over from their womenfolk the task of making pottery in most ancient cultures. The villages of the Near East were now growing into towns. More pottery was needed. Probably this need for increased pottery production proved impossible for the women to do with their considerable commitments to child rearing and food preparation. Although one person can make pots more quickly with a wheel, still more full-time labour is needed to decorate, finish and fire this increasing amount of pottery. Clearly, in all communities many people now became full-time potters from the third millennium BC. onwards.

It appears that predominantly matriarchal village societies gradually became dominantly Patriarchal as bigger urban communities became more organized and complex. (These important social changes could be studied elsewhere in more detail.)

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Need for modifications

Existing potter’s wheels in rural areas work on the principle of the worker spinning the wheel with his hands. This implies that the potter has to stop shaping the clay with his hands to spin the wheel. This results in unnecessary fatigue of the potter and time wastage in completing a given job. This in turn directly affects the economic welfare of the potter.

Also the speed of the potter’s wheel must be constant for quality production. Good finishing and desired widths at different parts can be achieved only by constant speeds. This is not present in existing potter’s wheels.

Pottery is slowly but surely becoming a dying art. One of the main reasons is the inability to create lots of pottery in a short time. A basic potter’s wheel cannot be used to produce pottery on a large scale.

With improvements in science coming in leaps and bounds, most of the western nations have already implemented various modifications to keep alive the joy of pottery. In India, modifications are still vapour ware.

We as engineers are forever looking to increase the efficiency in any mechanical system. It is obvious the existing model of potter’s wheel can be made way better by using it in tandem with mechanical devices like all bearings etc. We, as model human beings, are interested in the prosperity of others around us also. We believe our model of potter’s wheel will help potters living in rural areas.

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Aim of our Project

Having looked at the requirements for modifications, it is realized to make the potter’s wheel operable by some other part of the body other than the hands. This logically led to the consideration of the foot as the source of power. This leaves the hands of the thrower free to work on the clay lump. We also decided, after considering the conversion and ratio of speed, to include various mechanical systems like bevel gears, journal and ball bearings, chain sprocket drive etc. We also had to keep in mind that this potter’s wheel will most probably be implemented in the rural areas, and so the cost of materials and construction had to be minimum.

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DESIGN OF POTTER’S WHEEL

Before going to fabrication of potter’s wheel, it is desirable to design each and every components discussed below.

Bearing:

Bearing is a machine element which supports another moving machine element known as journal. it permits a relative motion b/w thee contact surfaces of members while carrying the loads. In order to reduce frictional resistance and wear and in some cases to carry away the heat generated lubricant may be provided.

Classification of bearing

According to direction of load to be supported.

1. Radial bearing 2. Thrust bearing

According to nature to be contact.

1. Sliding contact bearing 2.Rolling contact bearing

Bearing material: 1 Babbitt metal

Teen base babbit- Sn 90%,Cu 4.5%,Pb 0.5% Lead base babbit-Pb

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84%,antimony 9.5%,Cu 0.5%2.Bronzes (Alloys of Cu,Sn,Zn)3.Cast iron4.Silver

Lubricants: The lubricants are used in bearing to reduce the friction and to carry away the heat generated by friction.

Terms used in hydro dynamic journal bearing:

D= Diameter of the bearing,

D= diameter of the journal,

l= Length of bearing,

1.Diameteral clearance:

c=D-d

2.Eccentricity: It is the radial distance b/w the centre of the bearing and displaced centre of the bearing under load.

Coefficient of friction:

= coefficient of friction,

Z= Absolute viscosity of the lubricant kg/m-s,

N= Speed of the journal in r.p.m,

P= Bearing pressure on the projected bearing area in N/mm2,

d= Dia.of the journal,

c= Diameteral clearance,

k=Factor to correct for the leakage

=0.002 for l/d ratio of .75 to 2.8.

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Bevel Gears:

The bevel Gears are used to transmitting power at a constant velocity ratio b/w to shafts whose axes intersect at a certain angle. Two important concepts in gearing are pitch surface and pitch angle. The pitch surface of a gear is the imaginary toothless surface that you would have by averaging out the peaks and valleys of the individual teeth. The pitch surface of an ordinary gear is the shape of a cylinder. The pitch angle of a gear is the angle between the face of the pitch surface and the axis. The most familiar kinds of bevel gears have pitch angles of less than 90 degrees- cone shaped. This type of bevel gear is called external because the gear teeth point outward. The pitch surfaces of meshed external bevel gears are coaxial with the gear shafts; and the apexes of the two surfaces are at the point of intersection of the shaft axes. Bevel gears that have pitch angles of greater than ninety degrees have teeth that point inward and are called internal bevel gears. Bevel gears that have pitch angles of exactly 90 degrees have teeth that point outward parallel with the axis and resemble the points on a crown. That's why this type of bevel gear is called a crown gear.

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Classification of Bevel gears: according to angle between the shafts and pitch surface

1. Mitre Gears: When equal bevel gears having equal teeth and equal pitch angles connect two shafts whose axis intersect at right angle.

2. Angular Bevel Gear: When the bevel gear connects two shafts whose axis intersect at an angle other than right angle.

3. Crown bevel gears: When the bevel gears connect two shafts whose axes intersect at an angle greater than a right angle and one of the bevel gears has pitch angle of 90 degree, then it is known as a crown gear.

4. Internal bevel gears: when the teeth on the bevel gears are cut on the inside of the pitch cone,

Then they are known as internal bevel gears.

Advantages

This gear makes it possible to change the operating angle Differing of the number of teeth (effectively diameter) on each wheel allows mechanical

design to be gained. By increasing or decreasing the ratio of teeth between the drive and driven wheels one may increase the ratio of rotations between the two, meaning that the rotational and torque of the second wheel can be changed in relation to the first.

Disadvantages

One wheel of such gear is designed to work with its complementary wheel and no other. Must be precisely mounted.

The axes must be capable of supporting significant forces.

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Chain sprocket drive:

Chain sprocket drive is a way of transmitting mechanical power from one place to another. It is often used to convey power to the wheels of a vehicle, particularly bicycle and motorcycle. It is also used in a wide variety of machines besides vehicles.

Most often, the power is conveyed by a roller chain, known as the drive chain, passing over a sprocket gear, with the teeth of the gear meshing with the holes in the links of the chain. The gear is turned, and this pulls the chain putting mechanical force into the system.

Chain Drive Design Recommendations:

For optimum drive performance the following points should be considered:

Sprockets: For long life, sprockets should have a minimum of 17 teeth. For smoother, quieter drives use a minimum of 23 teeth.

Drive Ratios: Ratios of 12:1 or greater are possible but above 8:1 it is usually desirable to make the reduction in two steps.

Shaft Center Adjustment: Center adjustment to allow for wear is always desirable. It is particularly important in vertical center drives. Typically the amount of adjustment should equal 1% of the pitch.

Shaft Center Distance: The center distance should be great enough that the chain wraps the small sprocket at least 120°. Center distances should generally not exceed 60 pitches.

Chain Length: Whenever possible, chain length should be an even number of pitches so an offset section can be avoided.

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Tensioning Devices: An idler sprocket or shoe can often be used to maintain tension on fixed center drives.

Chain Width: The use of a wider than recommended chain will result in a more rugged drive and improved drive life.

Chain Casings: Fully enclosed drives with proper lubrication are desirable for maximum service life and personnel safety.

Non-horizontal And Vertical Shafts: Drives using non-horizontal shafts often work best with side guide chain and an automatic tensioned. Consult Ramsey for specific recommendations.

Drive Positions

The preferred position for a drive is that where a fine between shaft centers is horizontal or inclined not more than 45 degrees. Under ordinary conditions the slack strand may be either on the upper or lower side of the drive.

Vertical drives should be avoided if possible. They must be run fairly taut which means frequent adjustment of centers as the chain elongates due to normal wear. Less care and adjustment will be required if the drive can be positioned slightly off the vertical as illustrated.

cWhere the center distance is comparatively short, slack on the lower strand is preferable. With the slack

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on the upper strand there is a tendency for the chain to be forced out of proper engagement with the sprockets.

Design of chain drive:

Relation b/w pitch and pitch circle Diameter:

D= Diameter of pitch circle,

P= Pitch of chain drive, and

T= Teeth on sprocket.

Velocity Ratio of chain drive:

Length of chain drive:

Drives with long center distances and small sprockets should have the slack strand on the bottom. With the slack on top there is danger of the upper strand hitting the lower as the chain elongates.

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Shaft

A shaft is a rotating machine element which is used to transmit power from one place to other.

Types of shaft

1. Transmission shaft

2. Machine shaft

Material used for shaft.

Material used for shaft is carbon steel of grades 40C8,45C8,50C4 and 50C12.

Stresses in shafts

1. Shear stress due to transmission of torque

2. Bending stress, tensile or compressive.

3. Stresses due to combined torsional and bending loads

Design of shafts:

Shaft subjected to twisting moment only

Equation for calculation of diameter of shaft

T= Twisting moment acting upon the shaft

= Torsional shear stress

J= Polar moment of inertia of shaft about the axis of rotation

r= Radius of shaft

Shaft subjected to bending moment only

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M= Bending moment

I= Moment of inertia of cross-section area of shaft about the axis of rotation

Bending stress, and

Y= Distance from neutral axis to the outer most fibre

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A CATIA design of our modified potter’s wheel

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Modified potter’s wheel

Advantages

This potter’s wheel eliminates the use of arms as the propeller of the flywheel. Instead the feet are used to make the flywheel turn. This motion is caused by easy cycling motion. This increase the ergonomic index of the pottery area.

The potter’s wheel includes various mechanical systems that were previously missing. This increases the efficiency of the system by reducing losses due to friction, fatigue etc.

Rate of production of pottery will increase due to easy production. This will directly help uplift the lifestyle of the potters.

Disadvantages

This potter’s wheel can be driven at a constant speed only by moving the feet at a constant rate. This might prove irritating for the thrower.

Also this potter’s wheel doesn’t eliminate the need for human force application; it just reduces it. Using other systems like electrical motors etc., we might be able to achieve constant speed and minimal effort.

Cost of fabricating might still be high for the potter’s from economically backward areas.

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Bibliography

en.wikipedia.org

www.ceramicstoday.com

www.danmacleod.com

www.pottersguild.com

A Textbook of Machine Design by R.S. Khurmi and J.K. Gupta, S.Chand Publishers

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