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Mortise and Tenon Joints
 
 
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A mortise and tenon joint is a traditional blacksmithing method of joining metal. Not only is it inherently strong but it can be used, in a very expressive way, as a design feature. The photo essay below explains it's construction

 

The first stage is to form a swelling towards the end of a bar. This is done by very localized heating and pounding the bar down on an anvil, a process referred to as "upsetting"

This swelling is then hammered flat, pushing metal towards the sides of the bar. This helps form the wide shoulders on the tenon that give it strength.

To prevent the shoulder from distorting as the tenon is formed, it is defined by hammering a sharp groove all round the bar

The tenon is then roughly formed by drawing out (hammering) the metal in the isolated section at the end of the bar.

The tenon is finished by squaring up the shoulders.

The mortise is formed by hot punching a slot in the other bar to be joined.

The tenon is heated and inserted into the mortise.

The end of the tenon is hammered causing it to swell inside the mortise; creating a very strong joint.

The tenon is reheated and hammered flat onto the other bar.

In this case a decorative slit is punched into the flattened tenon which is then ground to a satin polish

This image shows the wide shoulders formed on the tenon; adding to it's strength.

A alternative way of finishing the joint is to punch a small slot through the tenon and driving a wedge through the slot

Or if a round tenon is used it can be hammered over to form a rounded "rivet" head.

 

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