Explain the general classes of joints according to the manner in which the pieces are joined.
There are two general classes of joints according to the manner in which the pieces are joined.
(i) Plain or butt joint
(ii) Lap joint
(i) Plain or Butt Joint
That is a joint in which the end or side of one piece is placed against the end of the other.
Further Classification of Plain or Butt Joints
(a) Straight (b) Corner (c) Dowel pin (d) Splice (e) Feather
a. Straight Joints
These joints may be classed as side or end according to the way the pieces are joined along with their sides of ends. This is the simplest form of joint and mainly used for flooring, boat planking etc. In furniture it is used for drawer bottoms or light cabinet work.
b. Corner Joints
There are two types in corner joints, on is square corner joint and other is mitered corner joint. If the butt and of one piece is joined against the other at right angles it is called square cornered joint. If the two pieces are joined at an angle, the joint is then called mittred joint.
c. Dowel Pin Joint
The joint can be substitute for mortised joint. This is simply a butt joint which is further reinforced with dowels Ritting tightly in holes drilled in each member.
d. Splice Joint
The joint is similar to double strap butt joint used on longitudinal seam of boiler shell. This is sometimes called fish joint.
e. Feather Joint
In this joint a groove is made in each of pieces to be joined and a tongue of feather is inserted.
(ii) Lap Joint
In these joints the pieces are joined by laping on each other, hence named as lap joints.
These are classified as,
(a) Rabbetted Joint or Housed Butt Joint
(b) Mortised and Tenon Joint
(c) Scarf Joints
(d) Dovetail Joint
(e) Tongue and Groove Joint
(f) Bridle or Open Tenon Joints
(a) Rabbetted Joint or Housed Butt Joint
It is sometimes called housed butt joint also. A rabbet is cut across the side of one piece near the end and other piece will sit in It. This joint can be made water light and hence it is used for tanks and sinks.
(b) Mortised and Tenon Joint
It is simply called Tenon Joint also the Mortise (female) and Tenon (male) must exactly correspond in size so that the tenon should accurately fit In the mortise when the tenon and mortise do not extend through the inortised part it is called a stub tenon. This type is used where the joint will not be subject to any tension. When the tenon may project into or through the timber it is called a through tenon joint.
(c) Scarf Joints
it is an endwise lap joint to form one continuous piece without increasing in thickness, when assembled. They are named according to the nature of stresses they are to resist.
(d) Dovetail Joint
it is defined as a partially house tapered mortise and tennon joint. This joint has more strength than mortise and tenon joint.
(e) Tongue and Groove Joint
It has a tongue formed in one end and a groove in the other end then both are joined. This is used in flooring or making boards.
(f) Bridle or Open Tenon Joints
The joint is used in connecting parts of flat and molded frames and where a strong framed ground work is needed.
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