Kelvin's Circular Arch

The Bulls Eye was completed in June '10.
Here's a photo of Carl video-recording Kelvin...

Photo taken 18th June '10

...and here's the videos...

Video taken 18th June '10

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A bull’s-eye consists of two identical semi-circular arches, but the method of constructing the lower half is quite different from turning the upper half.

Photo taken 16th April '10

The brickwork is built up to the horizontal centre line of the bull’s-eye, racking back from the extrados of the invert arch

The extrados is the outside edge of the arch and inverted means up-side-down

Image from BDA

The wall should be sufficiently high to support the timber beam from which the trammel will swing

The brickwork must be accurately lined through and plumb so that the entire circumference of the bull’s-eye will align with the completed wall

Image from Nash

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Image from Cartwright

As can be seen, the trammel can be attached to anything as long as it is secure, although these Austrialian methods tend to lack Health & Safety

Image from BDA

Photo taken 29th April '10

Photo taken 29th April '10

Image from Kreh

Wedge-shaped joints between uncut bricks in a rough-ring bull’s eye are generally considered unsightly

Image from brick stockist

Most bull’s-eyes are of axed brickwork formed by wedge-shaped bricks called voussoirs with parallel joints between.

It is possible for a skilled bricklayer to set out an axed bull’s-eye, make a cutting template and produce voussoirs by hand using a hammer, bolster and comb hammer

Bench-mounted masonry saws would be required to cut both hard and perforated bricks cleanly.

Image from Crawley bricks

However, most brickmakers can readily supply purpose-made tapered arch bricks provided they are ordered in advance

The majority of manufacturers have computer-aided design (CAD) facilities to determine the sizes of arch bricks

Photo taken 30th April '10