A
hot punched hole is characterized by the swelling of the steel either side of
the hole. This can be an attractive design feature and makes the bar much stronger
than if a drilled hole were used. When a bar is drilled, material is removed and
the bar is considerably weakened. However in a punched hole, material is moved
to the sides as a punch is forced through the hot steel. The process is illustrated
below.
Steel
bars are cut to size and heated in a forge. Traditional coal
forges can be more versatile but a gas forge is more suited for production
work. The steel is heated until it is almost white hot. At this temperature it
becomes soft enough to behave like clay and can be shaped by hammering on an anvil
A
slit is made by punching a blunt chisel shaped tool through the bar which is supported
by the anvil. The length of the tool keeps the smiths hand away from the hot steel
Very
little metal is removed making this slit, maintaining the strength of the bar.
The
steel is reheated and a tapered drift is punched through the slit, opening it
up by pushing metal to one side.
The
drift is punched through the bar, over the pritchel hole on the anvil, until it
drops through the bar and hole.
Hot
punched holes find many application in contemporary metalwork. Here they are used
to join bars running side by side. The bars are separated by spacers and the overall
effect is much more attractive than a welded joint.
Here
the swelling adds interest as other bars are passed through the holes. Punched
holes follow the shape of the drift used and so can be any shape including square.
Drilled holes can only be round.
Here
the holes are used as mortises
to receive the tenons in an interpretation
of a traditional woodworking joints.
