Stone Cutting Manual Information required

["Patrick McAfee" <mcafee@xxxxxxxxxx>]

In reply to Guy Aerts recent request for information the following may help.

Granite boulders and many other stones are split using plug and feathers.
This is common practice today with a history originating in roman or
possibly even pre-roman times. Each set consists of a centre plug slightly
wedge shaped and two feathers neary semi-circular in section, all in steel.

A series of holes are drilled at say 4 to 6 inch centres (100mm to 150mm) to
a depth at least equal to the lenght of the plug and feathers. Sometimes the
holes are drilled all the way to the bottom of the stone to ensure very
accurate splitting. The plug and feathers are inserted in the hole and
struck in rotation with a sledge (with compressed air nowadays).

The diameter and length of the plug and feathers varies from about 3/4" to
1.5" (20mm to 40mm) and the length from 4" (100mm) to a number of feet.

Originally the holes were drilled using a hand held bullnosed chisel called
a 'jumper' which was continually twisted as it was hit with a sledge hammer.
Compressed air is now used with heavy hammer action drills. For small work
an electric heavy duty hammer action drill is sufficient. I use 18mm plug
and feathers 6" (150mm) long with an electric drill in order to square up
stones for corner or quoin stones in wall building. They are then pitched
and punched to accurate dimensions. These will easily split a stone 12"
(300mm) to 14" (350mm) deep.

For splitting large granite boulders compressed air must be used for
drilling and the larger sized plug and feathers. In this case it may be best
to ask a local quarry with the equipment to do the work. The holes must be
aligned if an accurate split is expected and also the drill needs to be held
plumb while drilling and not allowed to go off at an angle. I have seen
granite boulders c. 8 feet (2.4 metres) high accurately split this way.

Here in Ireland the removal of granite boulders is rightly considered
illegal in certain scenic/cultural/heritage landscapes.

Another technique for splitting or cleaving granite was the 'pick and
wedge'. A pick was used to start the hole and then the hole was 'bottomed
out' with a special chisel. An iron wedge was inserted and struck with a
hammer. This was used for smaller work and not large boulders. A series of
wedges were inserted and struck with a sledge. If the holes were not deep
enough the wedge could fly out of the hole like a bullet. The wedges were
not always struck in rotation. A skilled man would change the rotation to
produce the most accurate split. The result is a distinctive tooted edge on
the cleaved granite.

Patrick McAfee
http://homepage.eircom.net/~mcafee/