Construction Techniques
When selecting a construction technique you need to
consider the following:
•What materials are being joined?
•How much load/stress has the joint got to take?
•Does the joint need to come apart or is it permanent?
•Are the aesthetics of the joint important?
•Is the construction suitable for the scale of production?
The construction techniques have been split as below:
Wood
Metal
Plastics
Frame Joints
Carcase Joints
Biscuit & Router Joints
KD Fittings
Screw & Nails
Soldering – Soft & Hard
Brazing
Welding – Gas & Electric
Rivets
Screw Threads
Welding
Frame Joints
Frame joints tend to be made up of long thin pieces of
wood forming rails and legs. They cover a wide variety
of applications. Typical uses include:
- Door Frames
- Chairs
- Table Frames
- Picture/Mirror Frames
- Window Frames
- Bed Frames
Mitre Joint
This joint looks good but it is not
interlocking so lacks strength. It
can be used to produce any
shape frame.
Cross Halving Joint
This joint can be used to produce
corners, ‘T’ shapes or ‘+’ shapes. In
a corner joint it is not interlocking so
relies on the glue for strength. The
most common use is in the ‘+’ form.
There are better joints for corners or
‘T’ sections.
This joint is ideal for smaller section
The fretwork on the
cabinet door shown left is
jointed using cross
halving joints
Bridle Joint
an interlocking joint.
used when a light frame is
needed and strength is not
the main requirement.
For example, a picture
frame.
Mortice & Tenon Joints
This is the most
common frame joint in
use. It has the same
gluing area as the
bridle joint but it is
contained within the
frame.
Carcase Joints
These are the ‘box’ constructions. The pieces of wood tend to
be boards rather than rails and legs. Typical applications for
these types of joints include the following
- Boxes of all varieties
- Chests
- Book Cases
- Cabinets eg. Bedside or Display
- Drawers
Mitre Joint
Veneer
Keys
Dowels
This joint is difficult to cut accurately. If it is too big for the mitre
saw it has to be planned by hand.
It is not interlocking so relies on the glue to hold it. The joint
can be strengthened by adding veneer keys or dowels as
seen above
Lap Butt Joint
A fairly easy joint to cut but it
lacks strength. It is not
interlocking so relies on the
glue.
Dowel Joint
A Dowel joint is created by
drilling matching holes in both
boards then inserting dowels to
provide some strength.
The dowels have
chamfered ends and
grooves cut along the
sides. This is to allow air
and glue to escape from
the hole. Fluted Dowels
To achieve accuracy a JIG is often used. This can be
made from metal and acts as a guide for the drill bit
Both Sides
of Corner
Comb or Finger Joint
interlocking and very strong
when glued but it does not
have the wedging action of
the Dovetail joint. It is quite
difficult to cut by hand.
Dovetail Joint
very strong and attractive joint. It has a large gluing area
and is interlocking. The wedge shape of the Dovetail
prevents the joint being pulled apart even without glue.
Housing Joint
This joint is used to form ‘T’
joints.
It is interlocking and strong when
glued.
It can be hidden by doing a
stopped housing joint
Biscuit Joint
machine cut joint.
can be used on corners on
in the middle of boards to
form ‘T’ joints.
The biscuit cutter is a small
saw blade that cuts a
groove in both sides of the
joint.
A biscuit is then glued in
between the two.
The glue makes the biscuit
swell giving a very tight
joint.
The biscuits are laid out to
mark where to cut
Both sides of the joint
have matching slots
The machine cuts the slots
The biscuits are glued in place
The Electric Router
The electric router can
be used to cut very
accurate parallel
housing joints. This is
ideal for jointing
manufactured boards
because the cutters are
available in the same
thicknesses as
manufactured boards
ie. 3,6,9,12,15,18mm
The Router can have different cutters inserted to give
different effects. These include cutting dovetails and
mouldings as shown below
KD Fittings
KD (Knock Down) Fittings are used in the industrial
production of furniture.
ideal for joining manufactured boards together.
knock down (take apart).
flat pack in boxes and assembled at home by the customer.
CNC machines are set up to drill all the holes in the
appropriate places ready for the fittings to push in.
The Modesty Block or
Corner Block is the most
basic KD Fitting.
Cam Fitting
Both parts fit into
pre-drilled holes
When pushed
together they are
locked in place by
rotating the cam
with a screwdriver.
Scan
Fitting
fittings will not decrease in strength if they are taken apart
several times because they are not gripping into the
chipboard.
A major problem with KD fitting constructions is that they
lack rigidity. An uneven floor can distort the shape of the
cabinet. This makes it difficult to use conventional hinges
because they have no adjustment. Special hinges had to be
designed
Hinges
The hinge shown above allows adjustment in 3 directions
Screws & Nails
When using screws you need to know the core and thread
diameters as shown above
The clearance hole is
the Thread Diameter
and the pilot hole is
the Core Diameter
Coach Screw
Coach screws are used for
large applications. They
are driven in using a
spanner because the force
required would be beyond
a screwdriver.
From the left these are Round Wire, Oval or lost head,
Panel Pins, Clout nail and a Staple
To increase the holding
power of nails they can be
dovetailed
This helps to prevent them
being pulled out.
Which Process?
Brazing
Welding
Yes
No
No
Yes
Yes
No
No
Aluminium
No
No
Yes but
difficult
Yes but
difficult
Steel
Yes
Yes
Yes
Yes
Stainless
Steel
No
No
Yes
Yes but
difficult
Soft
Solder
Hard
Solder
Copper
Yes
Brass
Rivets
produce fixed permanent joints or act as pivoting points
allowing two pieces to move over each other as in scissors or
shears.
Rivets must be made from a malleable metal as they need to
be shaped.
There are 4 common rivet forms that can be used which are
shown below.
An alternative to the traditional rivets is the Pop Rivet. This
is applied using a gun and is ideal if easy access is only
available from one side.
Fittings Involving Screw Threads
Thread details you need to know
Types of Fittings
BOLT
Machine
SCREW
Set
Grub
Screw
The pictures above show the 3 main fittings. A variety of
different heads are available that are driven in with a
screwdriver, spanner or allen key.
The most common nuts are hexagon nut or the wing nut that
can be done with fingers.
There are times when it is very important for the nut not to come
off eg. On a car wheel. There are 2 methods shown above, The
lock nut, the castle nut and split pin and the nyloc nut.
washers spread the load and prevent damage to the surface.
Washers can also prevent the nut coming off through
vibration. Shown below are a Plain Washer, a Spring Washer
and a Serrated Washer
Self tapping screws can join
non-ferrous metals or plastics.
They are made from hardened
steel and will cut their own
thread. A pilot hole must be
drilled first to the core diameter
Cutting Screw Threads - Taps and Dies
The Tap produces female threads
Tap Wrench
The split die allows slight
adjustment to the size of the
male thread. The Die is held
in a Die Stock shown below.
The adjustment is made by
adjusting the 3 screws
Construction Techniques Questions
Which joint would you use for a hexagonal picture frame?
Why is the joint on the left better than the joint on the right?
Which would be the best joint for the fret work cross below?
Why is the mitre joint not very strong?
Why is the dowel below not suitable for use in a dowel joint?
How can you accurately drill 10 holes all matching for a dowel
joint?
Why is a mortise & tenon joint better than a bridle joint because
they have the same gluing area?
Why is a lap dovetail used instead of a through dovetail for a
drawer front?
19-What is aesthetically unattractive with the housing joint
below?
The housing joint below would fall apart if pulled hard. Sketch how
the joint could be improved?
What does KD mean?
Why is the modesty block a poor quality fitting?
Why is the cam fitting more suited to repeated dismantling
than the modesty block?
Why do hinges on self assemble wardrobes need to have
adjustment in 3 directions?
How can you increase the holding power of nails?
Why is a coach screw driven in with a spanner instead of a
screwdriver?
Soft solder is an alloy of what?
Why is welding stronger than Brazing?
Why is welding Aluminium difficult?
Why does the metal in a rivet need to be malleable?
What is the thread pitch?
Where would you find a castle nut & split pin?
What tool cuts a female thread?
What is the main reason for using a washer?
Why are self tapping screws made from hardened steel?
When using brass screws in wood a steel one should be put in
first. Why?