in the design of hand tools

99 Pages·2009·0.78 MB·English

IrII iI Iff IllI fill I II
47515
OCCUPATIONAL SAFETY
AND HEALTH SERIES
No. 44
ERGONOMIC PRINCIPLES
IN THE DESIGN OF HAND TOOLS
T. M. Fraser
INTERNATIONAL LABOUR OFFICE GENEVA
ISBN 92-2-102356-7
First published 1980
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FOREWORD
The present publication is one of a series of the International
Labour Office on the subject of occupational safety and health.
It is intended to assist all those who are connected with the
design, manufacture, purchase and use of basic hand tools in the
developing countries as well as in industrially advanced countries.
Much of the anthropometric data used is based on studies in
Europe and North America but it can, nevertheless, be of value in
the design of hand tools for use elsewhere in the world.
This publication was originally drafted by Mr. T.M. Fraser,
Director and Professor, Centre for Occupational Health and Safety,
University of Waterloo, Ontario, Canada, and was subsequently
reviewed by a number of experts in the field of ergonomics repre-
senting a cross section of employer, worker, government and academic
circles drawn from different parts of the world. Their comments
and suggestions have been taken into consideration in the final
version of this text. The International Labour Office is grateful
to all who have thus contributed to the preparation of this publica-
tion.
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TABLE OF CONTENTS
Page
FOREWORD
PREFACE T11
CHAPTER 1 - TEE NATURE AND EVOLUTION OF TOOLS 1
Basic requirements for tools 1
Generic tools 1
Manually driven tools 1
Power driven tools 4
CHAPTER 2 - THE NATURE OF ERGONOMICS 8
Origin and development of ergonomics 8
The components of ergonomics 9
Man-machine-environmental systems and their
relationships to tools 11
CHAPTER 3 - HUMAN WORK, SKILL AND FATIGUE 12
Physical work 12
Energy resources 12
Distribution of resources and end products 14
Energy requirements 14
Muscle function 16
Skilled work 17
Fatigue 18
Management of fatigue 19
CHAPTER 4 - ANTHROPOEETRY AND BIONECHANICS IN RELATION
TO TOOL DESIGN 23
Functional anatomy - shoulder, arm, hand 23
Operational aspects of anthropometry in tool usage 26
Human dimensions and physical abilities 31.
Anthropoinetry 32
Joint rotation 35
Hand strength 35
Sex 35
..
Comparative male-female strength 36
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Page
CHAPTER 5 -. A PRACTICAL GUIDE TO HUMAN ENGINEERING
IN TOOL DESIGN
General requirements 38
Size of tools 47
Characteristics of handles for specific tools 48
Human engineering of hand tool controls and displays 61
Displays 66
CHAPTER 6 - DESIGN NETHODOLOGY 70
Environmental defect 72
Needs analysis 72
Definition of the problem 72
Development of design criteria 73
Development of alternative solutions 73
Analysis of feasibility 74
Optimisation 74
Selection of the solution 75
Implementation and communication 75
Significance of ergonomics in the design process 76
Testing of models and prototypes 77
REFERENCES AND BIBLIOGRAPHY '78
APPENDIX A - CHARACTERISTICS OF CONMON HAND TOOLS 83.
PREFACE
As the title would imply, it is the intent of this text to
discuss the design and usage of hand tools from the point of view
of ergonomics. For this purpose the material has been organised
in a certain, pattern. It is well to start at the beginning, and
consequently Chapter 1 begins with an outline of the evolution of
hand tools throughout history. However, one cannot discuss tools
from the point of view of ergonomics without first defining the
term and expanding on its nature. Chapter 2 is devoted to this
purpose.
Since the use of tools involves work, and since ergonomics
is concerned with man in his working environment, Chapter 3 examines
the physiological and psychological aspects of human work, skill,
and fatigue. This, in turn, leads to a discussion in Chapter 4
of. some of the limiting human constraints in anthropometry and. bio-
mechanics that determine the optimum design of hand tools and the
uses to which they can best be put. With the background established
in relation to history, human physiology and psychology, anthro-
pometry and biomechanics, Chapter 5 goes on to provide a practical
guide to the human engineering of hand tools and small power tools,
or in other words, defines wherever possible the optimum design
specifications for a variety of olasses of tool.
One area remains to be covered from the point of view of the
manufacturer, namely the principles of design itself. Chapter 6
is devoted to a discussion of design methodology. As a supplement,
there will be found in the Appendix a description of many of the
hand tools in common use.
While this text may serve several purposes, and hopefully,
may even provide some assistance to the designers, manufacturers
and users of hand tools in the established industrial countries,
it is primarily intended for those in developing countries who are
in process of entering the field and are seeking information which
is otherwise difficult to come by.
CH1PTER 1
THE NATURE AND EVOLUTION OP TOOLS
Basic requirements for tools
It will be apparent that tools have developed in an evolutionary
manner, perhaps aided every now and then by some gigantic intuitive
leap forward. With the hindsight of today, however, it is possible
to define some basic requirements for efficient tools (developed
from Drillis, 1963).
The tool must perform effectively the function for which it
is intended (e.g. an axe should separate wood fibres cleanly,
be easily withdrawn, and should convert the maximum amount of
kinetic energy into useful cutting or splitting work).
The tool should be properly proportioned to the body dimen-
sions of the operator (e.g. the ratio of the kinetic energy
at the instant of contact with the material to the total
energy expenditure during the full working cycle characterises
the efficiency of the movement and should approach maximum).
The tool should be designed to the strength and work capacity
of the operator (e.g. allowances should be made for the
operator's build, sex, and training).
The operation of the tool should be such as to produce least
fatigue (e.g. its use should not demand unusual activities or
postures on the part of the operator).
The tool must provide sensory feedback to the operator
(e.g. the hand should sense pressure, impact shock, texture,
temperature, etc.).
Generic tools
Over the 10,000 years or more of their specialised development
tools have assumed many forms, but certain clearly discernible
functional groups can be identified. The primary difference today
is in the distinction between manually driven and power driven
tools. In the former, of course, the motive power for operation
is derived from the operator alone, while in the latter, although
the operator may hold and direct the tool, the motive power is from
some external source. The development of each of these fundamental
groups is examined below. A description of contemporary common
hand tools is found in Appendix A.
Nanually driven tools
1. Percussive tools
Percussive tools are defined as those which require a propul-
sive force to deliver a blow. The basic representatives are the
axe and hammer, the axe having a cutting edge. Other differences
are determined by the weight, shape and material of the head, and
the length and angular relationships of the handle.
-2-
Thus a hammer consists essentially of a heavy head on a wooden
handle. When it is swung the kinetic energy of the head is impacted
to the object struck. The attainable energy depends on the weight
of the head, the angle through which it is swung, the radius of the
swing, the velocity of the swing and the magnitude of the applied
force.
There are many varieties of hammers. The contemporary model
originated with the Age of Metals and has changed little. A sledge-
hammer, weighing for example up to 3.3 kg (7 1/2 ibs) with a handle
of approximately 60 cm (24 inches), may be used double-handed for
heavy driving or working of wrought iron; a fitter's hammer with
a 0.9 kg (2 lb) head and a handle of 25 to 30 cm (10 to 12 inches)
is a single-handed tool which combines strength with speed; the
ballpeen or hemispherical back of the head is used for rivetting.
eologist's and boilermaker's hammers have longer narrower heads
for use in a restricted space and for concentrating the blow on a
smaller area. The back of a carpenter's hanmer may either have a
narrow straight edge for driving nails with small heads or a claw
for extracting nails. The claw hammer, in fact, is known from
Roman times. Heads made of soft metal, rubber, rawhide, or synthe-
tic materials may be used to avoid damage to the material being
struck. Some indeed may be hollow and weighted with lead, while
lead itself is used as the head of a plumber's dresser, and wood as
the head of a carpenter's mallet or a wooden maul.
Axes and adzes are also striking tools, but with a cutting
edge. The essential difference is in the relationship of the head
to the handle. In the adze the plane of the head is at right angles
to the handle. The weight and shape of the axe head is adjusted
to the operation it has to perform varying from 0.5 to 2.2 kg (1 to
5 lbs) or more.
2. Scraping tools
Saws: Primitive stone tools were of course scraping tools as
well as percussive tools, but the saw as an implement did not become
specialised until the seventh century B.C., with the beginnings of
the Metal Age. It was originally used with a pull cut. The push
cut utilised by most saws today originated with the Romans. Pruning
saws, fret saws, and coping $aws, with thin narrow blades, may have
pull cuts as also do powered reciprocating and sabre saws. The
concept of the M-shaped teeth, with variable set, was developed in
the Middle Ages, but the modern saw blade originated from rolling
mill stock in. the eighteenth century.
Piles: Piles also show their basic origin, in the antiquity of
rough Stone Age tools. Bronze files, characterised by their teeth
oriented in one direction, appeared as long ago as 1500 B.C., but
could not of course maintain their abrasive cut. They became
popular in the Iron Age and were common by 1100 A.D. Today there
are many varieties, distinguished by shape, size and by the presence
or absence of a handle, but essentially there has been no change
since the Middle Ages.
Chisels: The chisel originated in the stone hand-held axe.
As the Age of Metals began, copper chisels appeared, their edges
hardened by hammering. By the time that bronze replaced copper a
-3
wooden haft had been added to the chisel. With the use of iron,
different varieties appeared, distinguished by size and shape, ontil
by the eighteenth century some 70 different types could be counted,
including curved gouges. While most of these are no longer in use,
the basic chisel has remained almost unchanged.
Planes: No definite line of descent has been identified for
the plane, although one might suspect a derivation from the adze.
The first clearly identified users were the ancient Romans whose
plane was very similar to that of today. The major difference in
fact has been the addition of the top iron or double iron in
eighteenth century England. This device is an inverted plane iron
wedged over the cutting iron, which limits the thickness of the
shaving and assists its curl.
Drilling and boring tools
Drilling and boring tools, such as the awl, gimlet, borer,
and drill itself, are derived from the primitive use of abrasive
sand on the end of a stick. For many thousands of years the motive
power was supplied by rotating the stick between the hands. This
activity was eventually replaced by the use of a bow string wrapped
around the stick. The stick was then rotated by a sawing action
of the bow. The pump drill, which operated by the vertical move-
ment of a handle on a screw, was developed by the Romans, who even
added a flywheel to the system to maintain the motion. This method
continued to the present day where it is still used (without the fly-
wheel) in the operation of some rapid action screwdrivers. The
modern rotary-action spiral drill with handle and ratchet is a pro-
duct of nineteenth century mechanical development.
Screwdrivers and wrenches (spanners)
In 300 B.C., Archimedes utilized a screw system for raising
water; this may be the first recorded use of the screw principle.
By the first century B.C., however, very large wood screws turned
by hand spikes were in use in wine and. oil presses. The sane type
are still used today.
Metal screws, hand cut, began to appear in the fifteenth
century, followed by bolts and threaded nuts in the sixteenth
century which were fastened by a T-handle socket wrench. Wood
screws, started by an awl or drill, also came into use at that time.
With the increasing use of wood screws cane the need for a
screwdriver, which initially was a slot-bladed bit used with a
carpenter's brace, which itself was an early form o± drill. The
handled screwdriver, however, did not appear until the nineteenth
century, although it became common after 1850 in a variety of shapes
and sizes with the mass produotion of tapered gimlet-pointed wood
screws.
Box and socket wrenches also appeared by the early nineteenth
century, along with the adjustable sliding-jaw wrench which was
originally held (1830) by a wedge tapped appropriately into place.
Screw wrench patents appeared in 1835 and the familiar monkey wrench
in 1858.
-4
Holding tools
Spanners, wrenches, and screwdrivers also act as holding tools,
but a variety of specialised holding tools has also been developed.
Tongs or pliers date from the first working of metals. Later
forms differ chiefly in the shape of the jaws, which may be narrow
and rounded for twisting wire, elongated crosswise and grooved for
gripping, or with special hinges to ensure a parallel relationship
of the two faces a-b all times. The most complex devices are
found in the very wide variety of faces, sizes, linkages, and
handles of surgical and dental forceps, each of which is designed
for some special purpose.
Cutting tools
Cutting tools are derived from the primitive stone axe.
The most common form is the ]mife in which a hardened steel edge
is pressed with a sliding action against the material to be cut.
The variety is very great, from the general purpose pocket knife
to the agricultural scythe and sickle, or from the grossness of
the sabre to jhe precision of the scalpel. Each is distinguished
by characteristics of size, shape, handle, balance and weight,
although in all a sliding cutting action is used, the proportion
of sliding to direct forward movement being very high for the
cleanest cut.
Scissors, shears, and tinsuips are also cutting tools, each
of which has a shearing, cutting action with very little forward
sliding motion.
Power driven tools
Any kind of tool can be operated by some form of external
power. The decision to use manual or external power is generally
determined by the type of work and the productivity demanded. For
casual light work manual power is common; for heavier work with a
higher productivity requirement power tools should be considered.
Electric power tools, for example, will pay for themselves in an
industrial setting if used for eight hours or more per week (1-IMSO,
1969). The sources of power for coinmonpower tools are electricity,
and the internal combustion engine. Compressed air and explosive
changes are also used for special purpose tools which will not be
considered here other than to mention them in a broad general out-
line.
(a) Electric power tools
Portable electric power tools, of the correct type, properly
used and maiiatained, will relieve a workman of much of the physical
effort required in operating tools, although he will still have the
effort, which can be considerable, of holding and directing them.
Electric power tools are generally compact with one or two
hand grips. Most have a finger-operated trigger switch incorporated
into the main handle for starting and stopping the motor. Action
is sustained by holding the switch in position, or it may be main-
tained by operating a secondary catch which must be released -to stop
the action.