Joining Techniques Wood, Metal and Plastic

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Joining TechniquesWood, Metal and Plastic

• Design and Manufacture

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How to join Wood.

• There are 4 main ways to join wood an adhesive,
  a joint, a nail or screw or using a knockdown
  fitting. Common wooden products that you use
  every day will incorporate some of the joining
  techniques above.

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Gluing

• The majority of the time Polyvinyl acetate (PVA)
  wood glue will be used to join wood. PVA glue is
  used in the workshop every day and is the glue
  you would use to make paper Mache.

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Nails and screws

• There are many types of nails and screws to fit
  your needs. Some common ones are below.

Round head
Oval head
Countersink or flathead
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Knock-down fittings

• Knock-down fittings are those that can be put
  together easily, normally using only a screw
  driver, a drill, a mallet/hammer and other basic
  tools. They are temporary joints although many
  are used to permanently join together items such
  as cabinets and other pieces of furniture that
  are purchased in a flat pack.

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• Other glues that could be used would be
  Superglue, epoxy resin, Hot glue, and a number of
  different resin glues Phenol formaldehyde resin,
  Urea-formaldehyde resin.
• Before these modern glues the glue of choice was
  animal glue or hide glue. It is manufactured from
  rendered collagen from the skins (hides) of
  animals. It is chemically similar to edible
  gelatine and is non-toxic if ingested. Hide glue
  is still used today in specialized applications
  musical instruments (lutherie), for replica
  furniture, and for conservational-grade repairs
  to antique woodwork.

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Wood joints

• Butt Joint
• The most simple and easiest to make wood joint is
  the Butt joint. The joint relies solely on the
  strength of the glue to hold it together.

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Housing Joints

•  What is a Housing joint?
• Housing joints are used when two pieces meet at
  right angles on their narrow face. A shallow
  trench is cut across the grain of the vertical
  member, the shelf or panel is then glued into a
  simple straightforward housing and all the loads
  are transferred to the sides of the unit. Pins
  can further strengthen the joint.
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• What are the advantages of this type of joint?
•         Simple to make.
•         Strong.
•         In its basic form only one component has
  to be shaped.
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• What are the applications for this type of joint?
• Used for fixing shelves to vertical panels in
  deep cabinets, bookcases, storage units and
  boxes, or for drawer fronts and carcase/frame
  construction.

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Types of Housing Joints

•  Through housing joint
• The trench of the though housing goes fully
  across the piece of wood so the joint can be seen.

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• Stopped housing joint
• For decorative effect, the trench of the housing
  is often stopped short of the front edge of the
  side panel by some 9 - 12 mm. No part of the
  joint is visible from the front because the joint
  is completely concealed. This is particularly
  important where a high quality finish is required.

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Mortise and tenon joints 

•  What is a Mortise and tenon joint?
• The mortise and tenon is one of the most common
  joints used by woodworkers and is the traditional
  corner joint for sturdy frames. 
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• What are the advantages of this type of joint?
•         Neat and very strong.
•         Large surface area for gluing.
•         It cannot wobble.
•         Is difficult to pull out.
•         Most of the joint is hidden in the
  timber.
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• What are the disadvantages of this type of joint?
•         Can be fairly difficult to mark out and
  cut.
•         Poor resistance to tension, especially if
  badly fitted.
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• What are the applications for this type of joint?
• Used where maximum strength is important in
  window, door, chair, mirror, bed and table frames
  and frame-and-panel cabinets or external work
  like garden or street furniture (seats, tables
  etc)

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Through mortise and tenon joint
In a through mortise and tenon joint the end
grain is visible and the joint needs accurate
cutting for good appearance.
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Haunched mortised and tenon joint
In order to include a strong joint at the frame,
a haunch is introduced to the joint. The haunch
prevents the frame from twisting and makes it
firmer, giving it added strength. It also
increases the gluing area.
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Stopped mortise and tenon joint
This is the best joint for external work as most
of the joint is protected from the weather by
tenon shoulders. The joint is strong and
concealed and used in furniture construction
where a high- quality finish is required. The
stopped mortise and tenon joint is a good looking
joint because the tenon of this joint does not
show on the outside face. The depth of the
mortise should be three-quarters of the thickness
of the wood being joined.
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Dovetail

• What is a Dovetail joint?
• Dovetails are the strongest of all joints. The
  joint is made up of interlocking wedge-shaped
  elements called pins and tails that resist the
  forces applied to the joint. This joint looks
  attractive and, if well made, the decorative
  quality can be used to enhance projects. In other
  projects the joint can be hidden completely.
  Dovetail joints work best when in tension. For
  example, the most common application of the
  dovetail joint is in drawer making as the
  strength of the joints tails and pins resist the
  pulling forces applied to the drawer. Dovetails
  are so strong it is rare to see a drawer that has
  broken as a result of joint failure, even when
  put under frequent stresses.

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Finger joint
A finger joint or comb joint is a woodworking
joint made by cutting a set of complementary
rectangular cuts in two pieces of wood, which are
then glued. To visualize a finger joint simply
interlock the fingers of your hands at a ninety
degree angle hence the name "finger joint." It
is stronger than a butt or lap joint, and often
contributes to the aesthetics of the piece.
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Other common wood joints
Lap joint
Dowel joints
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How to join Metal.

• There are a number of ways to join Metals. Some
  common joining techniques are, rivets, adhesives
  and thermal joining.

Women riveting the side of an airplane panel at
Ford Motor Companys Willow Run bomber assembly
plant in Ypsilanti, Michigan, August 23, 1944.
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Riveting
                                                                                                                         

• Rivets are used to join plates together and they
  have been used for hundreds of years. Before the
  widespread use of welding, rivets were used in
  heavy industries such as ship building. The steel
  plates used to build ships such as the Titanic
  and the naval Dreadnaughts of World War One were
  held together by steel rivets. Rivets have
  largely being replaced by techniques such as
  welding and brazing. However, joining plates
  together with rivets is still a useful technique
  especially if the plates to be joined are quite
  small. Cold rivets are still used in school
  workshops although the modern pop-riveting
  technique is more popular.

Riveting video
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Adhesives

• Glues like in wood can also be used with metals.
  Glues like the epoxy resin can also be used to
  glue together sections of metal.

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Thermal joining

• Thermal joining means using heat in order to join
  metal together. Some methods of joining metal
  together using heat are welding, soldering and
  brazing.

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Arc Welding
Arc welding is a type of welding that uses a
welding power supply to create an electric arc
between an electrode and the base material to
melt the metals at the welding point to create a
permanent joint.
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Brazing

• Brazing is a metal-joining process whereby a
  filler metal is heated above melting point and
  distributed between two or more close-fitting
  parts by capillary action. The filler metal is
  brought slightly above its melting temperature
  while protected by a suitable atmosphere, usually
  a flux. It then flows over the base metal (known
  as wetting) and is then cooled to join the work
  pieces together. It is similar to soldering,
  except the temperatures used to melt the filler
  metal are higher for brazing.

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Soldering

• Soldering is a process in which two or more metal
  items are joined together by melting and flowing
  a filler metal (solder) into the joint, the
  filler metal having a lower melting point than
  the adjoining metal. Soldering differs from
  welding in that soldering does not involve
  melting the work pieces. Soldering is commonly
  used in electronics to create circuits.

Soldering video