Joining without heat: hemming riveting and beading

Heat changes the metal — it softens, discolours and can pull workpieces skew. Therefore the sheet metal smith and coppersmith have a number of joints that do without fire entirely. The mechanical cold joints are often both stronger and more durable than a soldered joint and are the standard in roof covering, gutters and large sheet metal items where soldering would be impractical or too weak.

A seam is a joint where two metal edges are bent around each other and pressed flat so they interlock. The simple seam is used for straight joints while the double standing seam is standard on copper and zinc roofs because it is watertight and accommodates metal movement from temperature changes. Seams are made with seaming tools and hammer or with a seaming machine and require edges to be bent precisely so the joint closes tightly throughout.

A rivet is a metal pin inserted through holes in two overlapping pieces and clinched (hammered broad) at the free end so it holds the parts together. Riveting has been used for millennia and is still used where a visible robust joint is desired or where heat cannot be used. In metalworking rivets are seen both as function (handles hinges fittings) and as decoration. The rivet must fit the hole and be clinched evenly so it doesn't become skewed.

Bording (also called edge bording) is the process of rolling or turning over a sheet metal edge, often over an inserted wire, so the edge becomes stiff, safe to handle, and holds its shape. A bordered edge on a bowl or tray prevents the rim from bending and removes the sharp metal edge. Edge reinforcement with inserted wire is a classic coppersmithing technique that gives a thin workpiece stiffness without making it heavy.

Choose cold assembly when

• 01The part is too large or thin for effective soldering
• 02The joint must be able to accommodate movement (take)
• 03Heat would pull the workpiece skew or discolour it
• 04A visible, crafted joint is desired
• 05Work is done outdoors where gas burners are impractical

“The best joint is not always the one that requires fire — sometimes it is the folded edge.”