Mortise and Tenon Joints

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hot forged mortise and tenon joint forged steel mortise and tenon joint forged steel mortise and tenon joint riveted head

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

tenon upset

The first stage is to form a swelling near the end of the bar. This is done using very localised heating and a process called upsetting.

upset swelling forged flat

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

butchered tenon

A groove is formed all around the swelling, this is referred to by blacksmiths as "butchering" and prevents the shoulders from distorting when the tenon is forged

forged tenon

The tenon is roughly formed by drawing out (hammering) the metal in front of the groove.

squared up tenon

Then tenon is finished by squaring up its shoulders.

hot punched mortise

A mortise is made by hot punching the other piece of metal to be joined.

tenon in mortise

The tenon is heated and inserted in the mortise.

upsetting and rivetting the tenon

A sledgehammer is used to upset the tenon and rivet it over.

rivetted over tenon

This shows the tenon after being riveted over and before it is cleaned up.

finished mortise and tenon

This is the completed joint. The riveted tenon has been given a satin polish whilst the groove chiseled into it is purely decorative.

wide tenon shoulders

The wide shoulders of the tenon give the joints strength.

wedged tenon joint

An alternative to riveting over the tenon is to punch a slot in it, then drive a wedge through this slot.

tenon dome riveted

Alternatively, the tenon can be domed over to make a rounded rivet head.