Cutting a Return HeadIntroduction for Stonemasons

When a stone has no plane (or flat) sides it is referred to as a random block. Random blocks are generally supplied direct from the quarry and range in shape, size and weight. You can refer to a

stone data sheet to establish the maximum size of random available. Large random blocks are normally placed on a primary saw to be cut into manageable slabs (a process known as

slabbing). Smaller randoms can have a plane surface applied by the stonemason.

Random Block

Sedimentary rock is formed by the deposition of multiple layers of sediment in a process known as lithification. Once deposited, the weight of new layers compacts previous layers with such a

force that they fuse together. Over millions of years the layers continuously build up before geological processes leave them exposed and accessible for quarrying operations. Common

sedimentary rocks include sandstone which is formed by the lithifaction of sand sized minerals and rock grains such as quartz and limestone which is formed from the remains of dead marine

organisms containing calcium carbonate.

Sandstone Limestone

Sedimentary Rock

Metamorphic rock is formed when rocks and minerals are subjected to a combination of heat and pressure. Slate is formed from the metamorphisis of shale and tends to retain a heavy

lithification which makes it easy to split. Due to its low porosity, slate is often used as a roofing material. Marble is metamorphisised limestone which has been crystallised. This type of stone is

commonly used for ornamental stonework such as statues and intricate carving work. When sandstone is metamorphisised it forms a rock known as quartzite.

Marble Slate

Metamorphic Rock

Igneous rock is formed by molten rock (magma) which has cooled and solidified or by ash produced by a volcanic eruption. There are various forms of igneous rock some of which are very hard and durable (granite and basalt) whilst others are lightweight and brittle (pumice). The rock can be formed due to volcanic eruptions or less visible forms of volcanic activity (in underground

magma chambers). Granite is a material commonly used in the stonemasonry industry in Scotland and is known for its high compressive strength and low water absorption.

Granite

Igneous Rock

When cutting a return head on a block of stone it is important to consider both how the stone has been formed and where it is to be positioned on a building. If for example, you are forming a

return head for an ashlar quoin, you must ensure that you cut the stone to the correct dimensions and to the correct (natural) bedding plane.

Bedding Planes

A key skill used by the stonemason when producing a return head is that of being able to accurately check a stone for square. It is recommended that you use a non-adjustable square for

this task. In the images above you can see the difference between a stone that is square and a stone that is not square. It is also common for the return head to be “twisted” which means that

you need to check for both square and plane.

Checking for Square

There are three common types of square used by the stonemason; the steel square, the sinking square and the stock square. Each square is used for different activities and offer different

functions. For example, the sinking square is adjustable so is excellent for checking the accuracy of checks and fillets but should not be used when squaring a stone as it can be less accurate that

a non-adjustable square.

Large steel square

Stock squareSinking square

Types of Square

A return head can be defined as a plane surface that has been formed at pre-defined angle to an existing face or

surface. It is normally cut at 90 degrees to the adjacent faces. The procedures for cutting a return head are similar to those used to produce a plane surface.

The significant difference is that the return head is cut plane and square to an existing face. This makes it slightly more challenging to get right and it is therefore important to continuously measure and monitor your work for

accuracy.

In the image shown the plane surface is indicated in red and the return head is indicated in green. Return heads are

most commonly cut on stones that are seen on more than one face such as

rybats and quions.

Stone Recognition

Stage 1: If working from a sawn six sides (S6S) block the stone will be measured and marked to the correct height using a scriber. If working from a random block the stonemason will have to produce a plane surface before moving to stage 2.

Cutting a Return Head

Stage 2: Once a plane surface has been established and the desired height of the stone (or length or width depending on which face the return head is being cut) is set, a square is used to mark lines at right angles to the plane surface.

Cutting a Return Head

Stage 3: Using the squared scribe lines as a guide, the stonemason sets in all four corners using the mallet-point, teeth tool and chisel. The sinkings adjacent to the face are checked for square. The sinkings opposite the plane surface are often left slightly high to allow for adjustments at the next stage.

Cutting a Return Head

Stage 4: A marginal draft is run between the sinkings to establish a square return head. It is essential that both drafts (at each side of the return head) are square and aligned. A square is used repeatedly to ensure accuracy.

Cutting a Return Head

Stage 5: Marginal drafts are then used to join either side of the return head. These drafts run from point to point and will be square provided the sides have been set in accurately.

Cutting a Return Head

Stage 6: The wastage in the centre is removed using a mallet-point, teeth tool and chisel. This process is identical to the process used to produce a plane surface so should be familiar to you. Once complete, the stone is either polished or applied with a surface finish.

Cutting a Return Head