Page 153 - CITS - ED - Mechanical

ENGINEERING DRAWING - CITS

Types of riveted joints

Types of riveted joints
– Lap joint
– Butt joint

When the plates are placed one above the other, the joint is called Lap joint. The distance between the centres
of adjoining rivets in the same row is called the pitch. (Fig 1)
In the lap joints only two plates are used placing one over the other and riveted. In butt joints, the plate ends are
placed face to face, single or double cover plates are used to rivet them together.
When the number of rows are two or more, rivets are arranged in chain or zig-zag formation. (Fig 2)

Fig 1 Fig 2

Types of lap joints
Single riveted lap joint: There is only one row of rivets. The plates to be joined are placed one above the other
to a lap length of 3d, d being dia of the rivet. In any riveted joint, the distance between the end of the plate to the
rivet hole is called `Margin' (m).
Riveted joints are named according to the number of rows of rivets, a single riveted lap joint has one row of rivets,
double riveted lap joint has two rows of rivets - triple riveted joint has three rows of rivets. The rows may be chain
or zig-zag. (Fig 3a & b)

Proportions of riveted joints: The diameter of rivet, pitch and margins are calculated to prevent failure of joint,
forming a safe and efficient joint. For all sizes, thickness of the plates is considered first.

– Diameter of rivet d = called Unwim's rule
– Pitch (Max.) P = 3d

– Margin M = 1.5d
– Min. Pitch = d + 30 mm
– Row pitch for chain riveting (Pr) = 0.8P
– Row pitch of zig-zag (Pr) = 0.6P

140
CITS :Engineering Drawing (Mechanical) - Exercise 8