The joint: a design telltale

In the engineering of any object, the joint between discrete materials and parts is a fundamental source of functioning but also a fundamental problem: a point of weakness and wear. Therefore, the integrity, aesthetics and ergonomics of joints are key criteria on which to judge the entire design philosophy informing the object.

Joints are static or dynamic. Static joints effect the transition between discrete materials in components such as frames, chassis members, panels and fairings. They are distinguished by having things done to them: rain strikes window glass and its frame; grass and debris are directed through the rotor fairing of a lawnmower. Dynamic joints allow work to be done in the interaction of their own parts. The typical example is a hinge. Dynamic joints are distinguished by what they do: they open a door; they actuate a steering system in an automobile; they make an office chair change its seat height or roll across the floor.

The structural possibilities for static and dynamic joints are defined as  mechanical, electromagnetic and chemical.

Mechanical joints include joints operating by friction alone or by interactions of parts relying on frictional, tensile and compressive forces such as hinges, staples, nails, cork stoppers, cams, catches, latches, gaskets, springs, washers and parts joined by threaded screws and bolts.

Electromagnetic joints use attractive and repulsive electromagnetic forces. They include solenoids, magnetic ball-and-socket joints, maglev bearings and magnetic connectors such as the Apple MagSafe power connector.

Chemical joints are a wide range of joints relying on chemical reactions which may be achieved by curing or interactions with reactants and a substrate. Examples of chemical joints are solder, welds, lubricants, fibreglass, resin-bonded carbon fibre, adhesives, and gap sealant such as Neoprene.

Design of joints should give first priority to fitness to purpose. Prefer solutions that have the best tactile feedback; do not interrupt flow in its ‘Zen’ sense; and are minimally vulnerable to fatigue, perishing and failure.

The failure of all joints is inevitable. Therefore modular design is preferable so that joints permit their own and other failed parts to be replaced by the user without specialised tools or knowledge.

Joints immediately signal design errors and virtues of all the types explained in this blog. The joints shown below are interesting means to study design trade-offs and compromises.

The black locking clip is not part of the hinge design

Above: Sleeve and bolt hinge in a wheeled rubbish bin. Durable engineering redeems degraded materials. Modularity is poor. Priority in the design is given to fitness to purpose.

Above: An ingenious combination hook-and-eye and cam latch. The fidelity to materials is high and the design has evident structure and good modularity. The element most vulnerable to wear, the rubber gasket, can be replaced easily and cheaply. Tactile feedback is poor because of the open wire construction of the latch, leaving little surface area for grip. It wobbles in use and the cam has no feedback until in or near the fully engaged position.

Above: The Sarpaneva pot by Iittala uses a very simple, hybrid mechanical-static joint, like furniture and tents which are designed to be collapsed or deconstructed repeatedly. Welds and/or rivets are the usual solution here. The natural materials have high integrity and good tactile feedback. The insulating properties of wood are functionally convergent.  Modularity is obviously good.

Basic design and performance criteria for watches

Above: Citizen Promaster PMX56-2811 in titanium
Below: Sinn UX with quartz movement in oil-filled case of tegimented steel

The wristwatch presents severe design and performance constraints due to its complexity and its form factor. Timekeeping accuracy, durability, legibility and affordability are the key criteria for a well-designed timepiece.

Automatic movements of any kind are ruled out immediately by their inaccuracy and bulk, particularly case thickness. Cases of more than 11-mm thickness are awkward on the wrist and damaging to shirt-cuffs. The best-made and most costly automatic movements in the world will lose or gain 4 to 15 seconds per day. If they are not regularly subjected to moderate physical force they will stop running within days. Thermo-compensated quartz movements may not show such variance in one year.

The most suitable material for watch cases and bracelets is titanium. It is best to leave aside soft,  precious metals such as platinum and gold which are fragile, kitsch liabilities in any watchmaking application. Steel also is easily damaged unless subjected to costly and complex hardening processes, is reactive to acid and is heavy on the wrist. Titanium, though vulnerable to marking and scratching  has about half the density and mass of steel for equivalent strength and has other properties functionally convergent to watchmaking such as low acid reactivity and hypoallergenic properties.

The most legible watch face achieves maximum contrast between white markings reversed from a black background. All mission-critical or ‘tool’ watches conform to this convention. Watches with chronograph and date complications are less legible than those with a rotating bezel. A bezel suffices for count-down and most other duties for which a chronograph is designed in daily use. Watches lacking hour numbering are less legible than those that are numbered.


To my knowledge the illustrated watches are first among the very few that satisfy most of these criteria. All have drawbacks: The Tudor Pelagos has an inaccurate automatic movement and has sacrificed hour numbering to minimalism. The Sinn UX is over 11 mm thick, is too large in all dimensions for everyday wear, has no hour numbering and requires special servicing at the manufacturer, albeit at long service intervals. The Citizen Promaster makes some concessions in build quality (eg, it has no ceramic bezel); the IWC Chrono Alarm suffers legibility compromises because of its chronograph displays, is no longer manufactured and its complex hybrid movement may be increasingly difficult to service at the recommended intervals.

The strengths of these designs are complementary to the weaknesses. The Tudor’s aesthetic presentation, bracelet clasp design and build quality are the most finely resolved. The Citizen’s solar-cell power source and monocoque case comprise the most technologically elegant design solution here. The Sinn is the most robust and, due to the oil-filled case, pressure-resistant and legible underwater. The IWC is suitably sized for everyday wear, and its extremely accurate hybrid, battery-powered movement behind its imposing case and face aesthetics would be one of only two in the list still operating after the watches had spent a month in a desk drawer.

Above: Tudor Pelagos in titanium
Below: IWC Chrono Alarm (now discontinued) in stainless steel with ‘Meca-Quartz’ calibre 631 hybrid quartz-mechanical movement

Sawaya’s kitsch abuse of Lego blocks

Artist Nathan Sawaya has appeared in the news recently for his kitsch abuse of Lego bricks. This is a perverse use of Lego as a building material. As a picture element the Lego brick functions poorly: it has extremely poor resolution, resisting Sawaya’s preferred use for it at every turn.

Shown below is a more appropriate use of Lego bricks. However, the exhaust manifold is non-functional and kitsch in the same way as a Sawaya sculpture is kitsch. It should be removed.