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	Cutting a Fan Radius

On This Page... Introduction   Layout   Using a cap stone   Poor Construction   Slow Curve   Decorative examples

Related Pages Flag Paving Cutting Flagstones  - Cutting Curves  - Inboard Cuts  - Cutting Notches  - Corners & Radii    - Ring Radius    - Fan Radius    - Run-outs and      Town Corners   Paving at Corners   Cut-in Block Paving   Tools & Suitability Using Hand Tools Cutting Mitres

 

 

Introduction This page is part of a series of pages that consider cutting techniques used with flags (or slabs, if that's what you call 'em). The first page examined the basic principles of cutting-in: this page looks at how the cuts for a Ring Radius are prepared; related pages consider other cut features such as notches, curves and flagged radii. See the menu above right or the related pages listing at the foot of this page for a more comprehensive guide to what's available.

Cutting a fan radius Fan radius layouts (also known as a "Splayed Radius" or "Spoke Radius") are normally only used where the radius is less than 10 metres and the rotation is 45° or more. Fan radius layouts are wasted on very large radii unless the origin is present or is only just obstructed/occluded, and where the sweep or rotation of the radius is less than 45° it can be difficult to identify that the layout is actually a fan. The flags or paving units used within a fan radius are normally double taper cut; that is, they are cut on two edges, and so they represent at least twice as much work as would be required to construct a ring radius. Accordingly, they tend only to be used for highly decorative and/or prestige projects.
Typical detail for a double taper cut fan radius
	In the photograph opposite, a fan radius has been double taper cut, as depicted in the diagram above. Note how, on the innermost courses, where individual flag pieces would have become exceptionally narrow and in breach of the 2:1 maximum plan ration recommended for flags, a "double piece" has been used to replace two single pieces. This is labelled in the diagram in an attempt to make it clearer. It's also worth noting that the example shown in the photograph features staggered joints within each "spoke" of the fan, whereas the drawing shows aligned or "stacked" jointing. A staggered fan is shown below.
Because a well-constructed fan radius involves a huge amount of skilled work, they are often cut in advance, using simple mathematics to calculate the angle of each cut and size of pieces required. This is particularly true for fad radii constructed from stone flags, especially those radii installed to public and commercial projects. Stone flags often required a significant quantity of dressing and processing to prepare them for use as paving. It therefore makes sense to undertake the necessary taper cutting in the same factory/quarry where the dressing/processing is carried out. The whole radius is then delivered to site and installed in a jigsaw-like manner by the paving contractor.

 

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Using a Cap Stone Where the origin of the radius is to be paved, a single piece known as a "Cap Stone" is used as the first unit out from the origin, rather than continue the spokes using ever smaller pieces reducing to nothing. This eliminates the need for excessive cutting and also eliminates the small 'darts' of flagstone that would otherwise be used. Obviously, this applies to quadrant radii and those of an acute (less than 90°) angle. When the radius is greater than 90° two or more cap stones may be used. An example of a double cap stone used with a 180° radius can be seen on the Ring Radius page

 

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What not to do
Concrete flags can also be cut off-site and delivered as a 'radius kit'. This is commonly done for the more decorative concrete flags, while the 'common' pressed flags are more usually supplied to site as standard units and cut to shape by the contractor. However, unless the laying operatives have a thorough understanding of the principles behind the construction of a fan radius, this can sometimes lead to paving installations such as the one shown opposite.
This fan radius, constructed using F70 concrete flags, has no two spokes the same. It would seem that the laying operative has cut each spoke to suit the assumed sweep of the radius rather than have each aligned to the point of origin, even though said origin lies within the building and is therefore obstructed. While there is nothing structurally wrong with this installation, it is not as aesthetically pleasing as a true fan radius and can only be interpreted as being the work of a lesser skilled contractor with no true understanding of fan radius layout. Sadly, this is largely due to the lack of proper training for streetmasonry.

In this example, which is patently of a poorer standard of work, the laying operative has almost no understanding of a fan radius and does not seem to have ever been shown how one is constructed. Uncut 'spokes' are interspersed with severely cut spokes, but as the uncut spokes approach the origin, they, too, have needed to be cut at an awkward angle to allow them to fit. Unlike the previous example, this construction is structurally incorrect. The severely cut spokes feature small, acute triangular pieces that are weak and highly likely to break. Compare this to the diagrammatic example shown above, where smaller pieces are replaced by larger pieces that cover two (or more) individual pieces, with no pieces being cut to a point, and no pieces being in breach of the 2:1 plan size recommendation.

 

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Slow Curve Obviously, not all applications for a fan radius will be quadrants or semi-circles. One of the most common applications that employs the principles of a fan radius, albeit on a larger but less apparent scale, is a simple curved path. As a flagged path curves one way or t'other, having the flags maintaining alignment adds to the aesthetics but is also a good indicator of the craftsman's artisanship. The photographs below illustrate what might be considered a 'basic' level of skill, where a simple 1200mm wide path has the B50 flags cut on a single edge to effect the change of direction. Compare this to the 2400mm wide path on the right, where the flags have had both edges cut (double taper) to form a much more visually pleasing pathway. The mix of old weathered flags with newer, cleaner replacements is less than ideal, but the implementation, the way in which the flags have been precisely cut with the intention of creating a classy piece of work contrasts sharp[ly with the 'minimal possible effort' model of the newer path.

Basic fan radius curve

Craftsman fan radius curve

 

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Decorative examples Finally, a couple of photographs showing fan radii used in more decorative situations. On the left, a small radius constructed from reclaimed flagstones and installed in what is increasingly being referred to as a "Heritage Area". The workmanship is fair, and the contractor obviously understood the principles involved, although the pointing around the setts and kerbs (which may have been installed by a different tradesman) leaves something to be desired! On the right, a fan radius laid as a perimeter ring around a garden feature. It should be apparent that these concrete flags are relatively old, quite probably in excess of 50 years, as evidenced by the surface texture and the crumbling at the arrisses. At least one flag has been replaced with a more modern unit. While it may have been simpler to construct this pavement as a ring radius, it was originally laid at a time when skill and craftsmanship of a streetmason were considered with far more respect and the tradesman has used this relatively simple and unimportant project to showcase his skills.
A small, fast radius fan constructed from reclaimed yorkstone paving.	A fan radius constructed to create a ring around a garden feature
In this example, the (slightly damp) flagstones have been precision cut off-site to create a curving pathway of shotsawn yorkstone with minimal jointing (3mm sand-filled, if you must know). Careful and precise garden design allows the flagstones to be custom prepared at the quarry and delivered to site as a kind of jigsaw-puzzle, ready to be put together to form the perfect pathway.
This four-spoke fan radius formed from Caithness Slate is a perfect example of a factory-prepared pavement section, cut and prepared to specific dimensions and then fitted on site against a bush-hammered granite kerb.
If ever there was a case for using a recess tray cover...why go to all the trouble of cutting a millimetre-perfect fan radius from flamed Greenmoor Yorkstone, only to have a god-awful nasty concrete-covered telecomms access box slap bang in the middle of it?
This image from Lincoln shows how it can look when you omit the telecomms nonsense!
A superb example of the art: a granite fan radius in the centre of Lanark. At its origin around the main doorway of the building, a ring radius in darker granite has been used, which then switches to a mid-grey granite fan radius when the diameter reaches around 3 metres. Each spoke is cut to perfection and the detail is completed by switching back to the darker granite for the final piece adjacent to the matching bull-nose kerb. The oil stains detract from its inherent good looks, but even so, it remains a thing of beauty.

 

Related Pages Tools & Suitability   Cutting Flagstones - The Basics   - Cutting Curves   - Inboard Cuts   - Cutting Notches   - Corners & Radii     - Cutting a Ring Radius     - Cutting a Fan Radius     - Run-outs and Town Corners   Using Hand Tools   Cutting-in Block Paving   Cutting Mitres