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A guide to specifying bespoke aluminium

Aluminium is a highly versatile, lightweight and strong material and can be worked using a variety of metalworking techniques.

An increasing number of architectural projects involve the specification of worked aluminium. To assist with this process and to ensure the product realisation meets your expectation we would like to share with you some important design considerations.

Bespoke working involves making items to specifier requirement on a one-off type basis. Job specific – quantities, sizes, shapes, radii, fixing details etc., are all incorporated into the finished item.

With each unique specification there is a first time for everything. It is always possible that unexpected developments can arise.

Practical consideration in terms of material performance and / or machine capabilities can therefore cause some variation to the originally specified requirements. Tolerances with specially made items are generally looser than those for manufactured parts.

Component size can have a critical bearing on overall job cost effectiveness. Closely compare preferred size requirements to standard stock configurations. Small dimensional adjustments are often possible and can achieve significant financial savings.

Corner radii on bent / formed items are determined by a combination of material thickness and alloy grade. A radius on the outside corner, of up to twice the metal thickness, is possible.

Countersunk holes cannot be provided on material thinner than 1.2mm.

Crazing of anodic coatings will occur due to mechanical influences such as forming or bending. Anodic crazing by cold deformations of all kinds can be avoided by ensuring that these precede the anodising process.

Dimensional tolerances apply to all bespoke products.

Grain structure on brushed surfaces is best designed to run vertically, this minimises dirt entrapment and eases cleaning. Mill and anodised surface finishes can clearly show the metal grain and it is therefore preferable to avoid adjacent component surfaces with conflicting grain direction.

Insulate at connections with other metals, for maximum durability.

Jig/clamp marks can ruin the decorative appearance of a finished component. When items are to be surface finished, please indicate the preferred area for clamping. If no suitable jig/clamp points are available it is sometimes necessary to specify ‘clamping tabs’ these can subsequently be cut away before installation.

Manufacturing (by others) is the mass productionof identical piece parts, same size, shape etc. Production tolerances and variations can be minimised by virtue of repeated processing, and therefore making the necessary adjustments to the next batch. However these production techniques are not generally appropriate for anything other than very large scale architectural projects.

Material flatness can only be subject to standard tolerances. Various stresses are released during the fabricating and shearing processes, these are sometimes impossible to completely alleviate.

Material loss will occur on saw cut items. Each saw cut removes material equal to blade width, normally 4 to 6mm.

Minimum thickness is not always the most economical life cycle option. Insufficient material thickness is a common cause of component failure or under performance.

One good side is normally supplied. Two good sides are only provided when technically feasible and by special written agreement.

Pattern matching on adjacently positioned textured and patterned sheets will often require additional material usage. Please state if this requirement applies.

Polythene film is usually applied to one side of sheet material to help protect the metal’s surface during workshop operations. Occasionally, depending on the process involved, the protective film may be accidentally ruptured, or might need to be removed in specific instances eg welding operations, subsequent surface finishing is therefore always advisable if aesthetic considerations apply.

Quantity tolerances do not apply on bespoke items supplied by GA, we produce to the exact number every time.

Surface finish is a subject which provides considerable scope for misunderstanding. During the metalworking process, materials inevitably suffer various forms of surface abrasion. Best practice usually requires the specification of surface finishing, if aesthetic considerations apply. These processes could include various applied finishes or mechanical surface treatments.

Weld-beads should be cleaned-off flush to the metal’s surface if decorative considerations are paramount, and can then be covered satisfactorily with a powder coat finish. If left uncoated, a cleaned weld can only be ‘blended in’ by mechanical treatments to the complete surface.

Welding is not compatible with the requirement for a decorative anodised finish. Various impurities in the metal are brought to the surface by the heat produced during the welding process and this often results in surface discolouration after anodising. Pre-anodised aluminium cannot be welded satisfactorily.

Gooding Aluminium are a national and international supplier of a wide range of high quality aluminium sheets, aluminium profiles and aluminium extrusions that are available in a variety of finishes.

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