Active learning ideas
The Gib and Cotter Joint is used to connect two rods of square or rectangular cross-section. This topic focuses on the disassembly of the joint into its constituent parts: the strap end, the rod end, the cotter, and the 'gib'. The gib is a special wedge-piece that provides a parallel bearing surface for the cotter and prevents the strap ends from spreading apart. This topic requires high attention to detail in representing tapers and interlocking surfaces.
Activity 01
Students use a U-shaped cardboard 'strap' and a wedge (cotter). They observe how the strap 'arms' tend to move apart when the wedge is driven in. They then add a 'gib' (a second wedge with a hook) to see how it holds the arms together.
What is the purpose of the gib?
Activity 02
Students draw the four individual parts of the joint. Peers use a checklist to ensure the 'taper' on the gib and cotter is consistent and that the 'hook' of the gib is correctly dimensioned.
How do the gib and cotter fit together?
Activity 03
Students discuss why this joint is used for square rods instead of round ones. They explore how the flat surfaces of the gib and cotter interact better with flat rod faces than with curved ones.
What are the proportions of the strap end?
A few notes on teaching this unit
Watch Out for These Misconceptions
Drawing the gib and cotter as a single piece.
Students often confuse the two because they fit so closely. Using a 'color-coding' exercise where they color the gib and cotter differently in the assembly before drawing them separately in disassembly helps clarify their distinct roles.
Forgetting the taper on the gib.
Students often draw the gib as a simple rectangle. It's important to show that the gib has the same taper as the cotter so that their outer edges remain parallel. Peer-checking the 'parallelism' of the combined gib-cotter unit helps correct this.
Methods used in this brief