Transcript Coping Saw - Shawlands Academy

Standard Grade Craft & Design
Revision Materials
Coping Saw
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Coping saws are used to remove complicated shapes and
cut curves in wood and plastic.
The blade is held in a frame and may be easily replaced if
broken.
The teeth of the blade point backwards towards the
handle.
The saw cuts on the pull stroke and not on the forward
stroke. This is because the blade is too flexible to be
pushed.
The blade can be angled in the frame if the frame gets in
the way when cutting larger sheet materials.
Tenon Saw
Tenon saws are used to make straight cuts in wood and
occasionally some plastics.
This type of saw has a stiff back and is suitable for detailed
cuts. The saws without this type of stiff back are more flexible
and are designed to cut large panels.
The tenon saw is generally used to cut woodwork joints.
The tenon saw is used in conjunction with the bench hook.
The bench hook is used to support the piece of wood while
it is being cut. It hooks onto the edge of a bench. The saw
has 12-14 teeth every 25mm.
Rip-Saw
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Large panels or sheets of materials, for example plywood or MDF,
require larger ripsaws in order to cut them by hand. Sheets that
are small enough may be held in the vice, but larger sheets may
need to be supported on special types of portable carpenter's
supports called trestles.
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Ripsaws are used to cut along the grain of large panels of real
timber. Panel saws are shorter in length to ripsaws and have finer
teeth, 10 teeth every 25mm. Ripsaws have 4-5 teeth every 25mm.
Because of its finer teeth and shorter length, the panel saw is
suited to thinner wood and sheets of manufactured boards.
Sawing – An Introduction
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Sawing is a way of separating the material that is not needed from the material that
is. The cut or gap that is produced by the saw is called the kerf. The kerf is usually
wider than the saw blade so that the blade does not get stuck when it is cutting
through the material. Bending alternative teeth from left to right produces this gap.
This bending of the teeth is called the set.
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Hacksaw blades are normally in the shape of a wavy cutting edge. It is important
when cutting to always cut to the outside of the marked line. This side of the line is
called the waste side. You must also leave enough room for filing and sanding.
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The choice of saw depends upon the type of material to be cut. Always use the
correct saw. Wood saws like tenon and panel saws are not hard enough to cut
through metal. Metal-working saws like hacksaws will cut through wood, but not
very effectively. Plastics like acrylic and polystyrene may be cut with coping saws,
but it is best to use a craft knife to slice the plastic along a straight line and snap it
over a hard edge.
Sawing Metal - Hacksaws
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Hacksaws and junior hacksaws produce straight cuts in metal. Both have
replaceable blades held in tension in the saw frame. The teeth face away from the
handle and cut on the forward stroke. This is the opposite effect to the coping saw,
which cuts on the pull stroke.
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The lengths of hacksaw blades are between 250mm and 300mm. The saw frames
can be adjusted to cater for both sizes. Like the coping saw, the blades can be
turned through 90 in the frame. This allows the hacksaw to cut larger sheets of
metal.
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Blades normally have 14, 18, 24 or 32 teeth every 25mm. This is called the pitch of
the blade.This is more teeth per blade than the coping saw, tenon saw, panel saw
and rip saw. Soft materials require a coarse pitch, less teeth, hard materials, a fine
pitch, more teeth. Three teeth should be in contact with the materials at all times. A
fine-pitched blade needs to be used for tubes and thin gauge materials.
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Sheet saws are like panel saws but with a hacksaw blade attached. These types of
saws are used to cut sheet metals and plastics. They also cut corrugated sheet.
Abrafiles
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The abrafile has a toothed, circular blade that fits into a
frame. Abrafile blades can fit into a hacksaw frame
using a pair of adaptors. Coarse, medium and fine
grades are available. Abrafiles are used to cut out
curves and rounded shapes from sheet metal.
Abrafiles are very good at cutting wall tiles.
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This image shows an abrafile blade in a junior hacksaw
frame.
Sawing Wood By Machine
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An electric fret saw has a reciprocating blade built
into a frame. This means that the blade moves up and
down and is pushed against the material. This type of
machine is ideal for fine, detailed shapes and cuts
small pieces of flat, sheet materials. It is very good for
making jigsaw puzzles.
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It does not cut thicker materials very well. It can be
used to cut plastic; a useful tip is to cover the part to be
cut with masking tape to stop the plastic's waste
sticking in the cut behind the blade.
Mitre Saws
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Mitre saws have a blade that can be adjusted
to any angle. The saw has cramps that allow
the material to be fixed to the frame while
cutting. The mitre saw may be used to cut 45°
corners for picture frames and mitre joints.
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The blade cuts on the backward stroke. It is
possible to buy electrical mitre saws. These
are called chopsaws.
Jigsaws
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The image above is of a 'Dewalt' portable
jigsaw. It is used to cut out complicated
shapes from large sheet materials like
plywood and MDF.
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The blades can be changed to deal with such
materials as metal and plastics. This type of
saw, like the fretsaw, has a reciprocating blade
that moves up and down.
Centre Lathe (Metals)
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When turning materials in a centre lathe:
the material to be turned is held in a rotating chuck
a cutting tool held in a tool post cuts the material
the shape of the cut depends upon the path taken by
the tool
the material will either be cylindrical in shape or flat
Casting
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Casting is a process where a metal is heated to such a high temperature, it turns to a liquid.
We call this a molten state. The metal is poured into a mould, left to cool and removed (in a
solid state).
When the metal (or plastic) is in this molten state, we say that it has reached its melting point.
The temperature depends upon the type of materials used. This is an essential feature in
casting and welding.
A company called Brambley Furniture produces aluminium cast furniture by traditional
methods using sand-casting and hand-carved wooden patterns. Today, aluminium is used
rather than iron and each piece is carefully finished in oven-hardened acrylic paint. The image
above shows an example of a Brambley garden furniture set. The chairs have been sand-cast
from aluminium and finished in an oven-hardened acrylic paint. Details are:
Material: aluminium
Composition: it is a pure metal
Properties: light, soft and malleable. It conducts electricity and heat very easily and can be
welded and soldered by a special process. Aluminium is a non-ferrous metal, meaning that it
contains no iron and will not corrode and rust if left outside. This is very different from cast steel
and iron, which rusts because they are both ferrous metals.
Uses: to make boats, aircrafts, railway coaches and foil for packaging and cooking. It may also
be used to make engine cylinder heads, pistons, cranks, window frames, saucepans and
electrical cables.
Manufactured (man Made) Boards
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Manufactured boards are made from natural timber. Sandwiching thin
sheets of wood together called veneers can make manufactured boards.
The veneers are glued together and compressed. Taking particles of
wood, mixing them with glue, compressing them and applying heat can
also make manufactured boards.
Very wide boards of hardwoods or softwoods are expensive and in some
case difficult to find. These sheets are also liable to warp. Joining narrow
boards end-to-end is time-consuming to prepare and again liable to warp.
Advantages of using manufactured boards Manufactured boards are
available in large sheets, much wider than is possible to cut from a tree.
The boards are stable (do not warp). Unlike timber, they do not absorb
moisture, dry out according to the weather, twist and split. Manufactured
boards may be sold in standard sheets of 1,525 x 1,525mm or 1,220 x
2,240mm in a variety of thicknesses.
MDF – Medium Density Fibreboard
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MDF is a type of hardboard, which is made from wood fibres glued under heat and
pressure.
There are a number of reasons why MDF may be used instead of plywood or chipboard:
It is dense, flat, stiff, has no knots and is easily machined.
It is made up of fine particles and does not have an easily recognisable surface grain.
It can be painted to produce a smooth quality surface.
Because MDF has no grain, it can be cut, drilled, machined and filed without damaging the
surface.
However, it can be dangerous to use if the correct safety precautions are not taken. MDF
contains a substance called urea formaldehyde, which may be released from the material
through cutting and sanding. Urea formaldehyde may cause irritation to the eyes and lungs.
Proper ventilation is required when using it and facemasks are needed when sanding or cutting
MDF with machinery.
The dust produced when machining MDF is very dangerous. Masks and goggles should
always be
worn. Due to the fact that MDF contains a great deal of glue, the cutting edges of your tools will
blunt very quickly.
MDF (Continued)
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MDF can be fixed together with screws and nails but the material may
split if care is not taken. If you are screwing, the screws should not be any
further than 25mm in from the edge. When using screws, always use
pilot holes. MDF may be dowelled together and traditional woodwork
joints may even be cut. MDF may be glued together with PVA wood
glue.
Oil, water-based paints and varnishes may be used on MDF. Urea
formaldehyde is always being slowly released from the surface of MDF.
When painting, it is good idea to coat the whole of the product in order to
seal in the urea formaldehyde.
Veneers and laminates may also be used to finish MDF. Wax and oil
finishes may be used as finishes, but they are less effective at sealing in
the urea formaldehyde.
The image above is of an MDF unit. It has been screwed together and the
heads of the screws have been covered with filler.
Plywood
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Plywood consists of gluing together a number of thin veneers or plies of softwood or hardwood.
There is always an odd number of veneers and each ply is at a right angle to the one below;
this gives the material its strength. The more veneers used, the stronger the plywood becomes.
Both the types of glue and veneers determine the suitability of a sheet for a particular
application. The finish quality of plywood varies considerably; some plywood has attractive
grains while others can contain knots.
Plywood is graded for exterior or interior use, depending on the water resistance of the glue
used to stick the plies together.
WBP - (weather and boil proof) plywood - exterior grade This type of plywood can be used
outside. Water-resistant adhesives are used and can resist a certain amount of moisture.
Sheds and cladding are made from this material. This plywood requires paint or varnish to
protect the outer veneer from the elements.
Internal plywood Internal plywood does not contain water-resistant adhesive. The code used
to represent this plywood is 'Int' - interior use only. It may be used for wall-panelling, flooring
and furniture.
Shuttering boxes These are made from shuttering plywood. Shuttering boxes are used in the
construction industry to contain concrete while it sets. The material is water-resistant to a
certain extent. The surface of this material does not have a decorative veneer and is generally
not suitable for use where an attractive quality finish is required.
Marine plywood This is made with waterproof adhesive so that it can be used underwater. The
material should still be protected with paint or varnish.
Chipboard
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Chipboard is made by gluing together wood particles with an
adhesive, under heat and pressure. This creates a rigid board
with a relatively smooth surface. It is available in a number of
densities: normal, medium and high:
Normal-density is fairly soft.
High-density is solid and hard. It is often used for kitchen tops (which are laminated with
melamine) and fire doors.
Medium-density is somewhere between normal and high density.
There are exterior grades of chipboard available but most are only suitable for internal use. All
grades of chipboard except the high-density variety tend to soak up water. Once it is
waterlogged, chipboard tends to swell and break down.
Chipboard with a veneered surface is widely used for flat-pack furniture and work surfaces.
High-density chipboard is often used as the carcass for kitchen units, worktops and flooring.
This type of chipboard is hardwearing, rigid and heavy. Other grades of chipboard are
standard, flame-retardant, flooring, and moisture-resistant. Ironing or gluing on strips of veneer
may disguise the unattractive edge of veneered chipboard.
The vpicture above is a typical, flat-pack bookshelf. It is made from chipboard with a laminated
outer surface.
Blockboard
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Blockboard is made up of a core of softwood strips. These strips may
be as wide as 25mm. The strips are placed edge-to-edge and
sandwiched between veneers of hardwood. The sandwich is then glued
under high pressure.
Blockboard is not suitable for outdoor use because the glues used are
interior glues. When using blockboard to make such things as doors or
tables, it is important to ensure that the core runs lengthways in order to
achieve maximum strength.
Blockboard may be used to make shelves, doors, panelling and partitions
and is sold in sheets of 2,440 x 1,220mm and is normally 30mm thick.
Screws and nails may be used to attach blockboard, but you have to
ensure that you make contact with the strips of softwood and not the gaps
between the softwood strips.
Ergonomics
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Ergonomics is the study of the relationship between people and their
environment. The 'environment' may be buildings, furniture, materials or
tools. Everything made, to be used by humans, has been ergonomically
designed. Designers may decide that their product is to be used by a
person of a particular height or weight. When you buy a bike, there is
room for adjustment, but it is very important that you choose the correct
size frame for your height.
Bikes come in all shapes and sizes. The difference in the frame size
depends on whether they are going to be used by children or adults.
There is even a difference between bikes used by men and women.
Designers may attempt to create products that are suitable for universal
use. This is difficult, as the products have to be adjustable in order to suit
the needs and sizes of a wide range of people.
Anthropometrics
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Anthropometrics is the study of the average dimensions of human beings. The
measurements of the people who will be using a product are taken and the maximum,
minimum and average sizes can be calculated. The design can then be made suitable for a
wide range of people. In order to design products that will be held or used by people, it is
essential to have collected hand and body sizes. We call these sizes anthropometric data.
This data is found in books available to designers, in which sizes, including details of human
reach and ideal working surface height are listed. Kitchen designers use this type of
information when designing new units.
Anthropometrics is really the study of the human form and human sizes. It involves finding out
such things as:
how far on average people can safely reach for objects
how much space they need
how much force they can apply to an object
Anthropometric data is found in charts and tables. It provides specific sizes such as finger
lengths and hand spans, but also offers average group sizes for people of different age ranges.
Other sizes to consider are height, reach, grip and sight lines. Game and toy designers need
to use this information for product design. Understand that these sizes are constantly changing
as the population grows.
Sensitive Design
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Designing for the needs of the minority is referred to as sensitive design.
Designing products for people with special needs, disabilities, the elderly and lefthanded people can make their lives much easier.
Special aids fitted to handles and taps, cups and kettles can help these people
manipulate objects that we find easy to manage and they may find difficult to
manoeuvre. People suffering from arthritis find it difficult to operate round door
handles with their fingers. It is much easier for them to move a lever with their
wrists or arms.
For many companies, the decision to design products for the minority involves
high financial risks and very low financial returns. If you think about it, the
needs of minority groups are similar to the majority: from time to time most of us
have dirty, greasy hands and fingers due to working outside. We may not wish to
hold the doorknob or tap handle. It would be a clear advantage to operate a lever
with a wrist or forearm.
People with arthritis may find it difficult to operate taps. The ergonomically
designed unit seen in the picture above sits on top of the tap and acts as a lever,
which may be pushed by a forearm.
Sensitive Design (Continued)
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Occasionally we all have difficulty removing
plugs from electrical sockets. This plug with an
integrated handle shown above would benefit
us all. It is an example of how the needs of a
minority group are the same as the majority.
Softwoods
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The cone-bearing trees called conifers produce softwoods. They are
generally evergreen and have easily recognisable needle-like leaves.
They grow in cold or cool temperate climates in countries such as
Canada, Scandinavia and northern Russia.
They grow much quicker than hardwoods. Softwoods take about 30 years
to grow. They are cheaper, softer and easier to work than hardwoods.
Their seeds are held in cones. Common examples are: pine, fir, spruce,
larch, cedar and the giant redwood.
The terms 'softwoods' and 'hardwoods' are used to describe the leaves,
seeds and structure of the trees, not the type of wood produced. For
example, balsa is light and very soft to use. It is used to make lightweight
models, but is a hardwood. Yew is a coniferous tree (softwood) but is
heavy and hard to use like some hardwoods.
Types Of Softwoods
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Material:Scots pine
Source:northern Europe, Scandinavia, Russia, Scotland
Colour:cream to pale reddish brown heartwood, cream sapwood
Advantages:one of the cheapest and most readily available softwoods.
It has a straight grain, is fairly strong and durable, easy to work and
finishes well
Disadvantages:knotty and sometimes has a blue stain from a harmless
fungus
Uses:it is the most commonly used softwood in Britain, suitable for all
inside work and if preserved properly, can be used outside
Hardboard
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Hardboards are a cheaper option to plywood, where strength is not required.
Hardboard is made from wood fibre, and is extracted from chips and pulped wood
waste. In the production process, the pulp is exploded under pressure. Heat and
steam are applied to leave fine, fluffy brown fibres. These fibres are transformed
into mats, which are held together with lignum and other glues.
The mats are then pressed between steam-heated metal plates to give grainless
sheets with one smooth, glossy surface and one textured surface. To prevent
warping, moisture is added in a humidification chamber. Hardboard cannot be
used outside because it absorbs water.
Three basic types of hardboard are available: standard, medium and oiltempered. Oil-tempered boards are impregnated with oil, making them stiffer,
harder and more resistant to scratches and moisture. A number of speciality
hardboards are available for specific purposes. These have embossed, perforated,
plastic-faced or veneered surfaces.
The bases of the drawers above are made from hardboard with decorative veneers
attached to them.
Plastics
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These garden chairs have been made from polypropylene, a form of
thermoplastic. They have been injection-moulded, are lightweight, easily
stacked and can be wiped down and cleaned after use. These are very
hygienic chairs because there are very few areas where particles of food
may be lost and bacteria form. They are inexpensive to buy because they
have been mass-produced and are sold in most garden centres.
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Material: polypropylene
Chemical name: polypropene
Properties: lightweight and floats. It has very good chemical resistance. It
is hard, can be sterilised and has a good resistance to wear and tear. It
has good impact resistance even at low temperatures
Uses: to make garden chairs, crates, waste and chemical pipes,
packaging film, battery cases, rope, sacks, carpets, car appliances, and
medical syringes
Common forms: powders, granules and rods
Density
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Density is the amount of matter in an object
(mass) per unit or space occupied by the
matter (volume). Relative density is the ratio of
the density of a substance with that of pure
water at a temperature of four degrees
centigrade.
Thermal Conductivity
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This is the movement of heat through a material or
substance. Space crafts have to endure extreme
changes in temperature. In space, the temperature is
very cold but on re-entry into the Earth's atmosphere,
the craft has to endure extremely high temperatures.
Fire resistant materials such as asbestos and silica
tiles are used to prevent the spacecraft from
vaporising on re-entry. The image above shows the
space shuttle. Image courtesy of NASA.
Semi Conductors
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These range between a conductor and an insulator.
They allow an electrical current to flow only under
certain conditions. They are used in electronic
components. They are made from silicon and
germanium. These two are poor conductors but when
mixed with other impurities, their electrical resistance
can be changed.
The moisture detector circuit shown above contains a
transistor, which is a small electronic switch.
Transistors process the information sensors. The
transistor is made from semi-conducting materials and
is affected by heat and light.
Thermal Insulators
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These are normally non-metals and do not conduct electricity very well. Usually plastics, they
may be used for such things as kettle or pan handles. It is safe for the user to pick up the kettle
with the phenol formaldehyde handle because it is a poor conductor and does not gain heat
very quickly.
It would not be safe to pick up the kettle by the stainless steel body because this material is a
good conductor and gains heat very quickly.
Thermal insulators do not gain heat quickly but also do not lose heat quickly. Air is a good
thermal insulator. Birds' wings trap air between the feathers, which keeps them warm in
winter.
Loft insulating and cavity wall insulation reduce the heat loss at home. Loft spaces and pipes
are lagged with this material. The lagging traps the air between it and the copper pipes. This
blanket of air prevents the pipes from losing too much heat and prevents them from cracking in
the winter.
THERMAL EXPANSION
Some materials expand when hot. The length of a steel bridge may increase in the summer. In
order to allow for this change in length, expansion gaps are built into the bridge construction.
Electrical Conductivity
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This refers to the movement of electricity through a
material. All materials attempt to resist the flow of
electricity to a certain extent; some materials resist it
more than others. Metals such as copper, gold, silver
and some gases allow electricity to flow through them
very easily. We say they are good conductors of
electricity.
Some materials resist the flow of electrical current and
are called good insulators. These normally include
the non-metal materials such as wood, glass and
plastics.
Veneering
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Veneering is the art of applying a thin sheet of decorative wood onto a
piece of wood that may be plain or unattractive. It is a very old technique
and was started in the 17th century. At the same time, people began to
import more exotic woods into the country. Exotic woods are rare and
expensive today. It would be too costly to make mass-produced furniture
completely out of an exotic wood like African walnut. As a result, gluing
veneers onto the surface of cheaper materials can produce manufactured
boards. It forms the basis of mass-produced furniture today.
Decorative effects can be achieved by matching veneers and making
patterns. This is called marquetry. The image above is of a cabinet that
has been veneered using decorative hardwood veneers. Cutting shapes
from the veneer and arranging them into geometric patterns has created
the patterns on the surface.