Case clamped shut

4 min read

The humble toggle clamp has been helping engineers to meet this fixing requirements for decades. The time has come to celebrate this permanent fixture of our industry.

In the age of industrial automation, engineers are getting excited about big data, autonomous machines and the possibilities brought about by connected systems. With all of this new technology being introduced at rapid pace, it can be easy to overlook the crucial static fixtures that, quite literally, hold these production lines together.

One such component is the self-effacing toggle clamp. They may be considered less glamorous than many other components used on productive assembly lines, but you’d be hard pressed to visit an engineering shopfloor that does not utilise a toggle clamp for the temporary fastening of parts.

One firm believer in their efficacy is Paul Mulvey, business development manager, norelem UK, who regards this clamp as an “unsung hero of industry”. He points to how the classic design of these components facilitates simple operation through a system of levers and pivots. “Once the clamp’s spindle contacts the workpiece, clamping force is exerted as the linkage elements compress together. Once the centre pivot moves past the centre-line of two other pivots to force a stop, the clamp reliably locks into place. This locking mechanism is secure enough to hold almost any component in place until the assembler releases the toggle by moving the handle. For manufacturers that have to transport parts over a manned station, this functionality makes the toggle clamp one of the most reliable and effective standard components in industry.”

However, while many operators are familiar with how a toggle clamp operates, few are aware of the careful design engineering that goes into the product to successfully couple reliability and functionality with ergonomics and convenience, he adds.

Although a standard component, toggle clamps come in a wide range of designs, with different applications requiring diverse locking configurations, including push-pull, latch, can, vertical, and hook operations. “All of these applications require different sizes and clamping pressures, so it is always advisable to seek assistance from a manufacturer or supplier such as norelem prior to specifying a clamp for operation,” advises Mulvey. norelem offers 36 varieties of toggle clamp, in over 120 sizes, for the clamping of workpieces by drilling, bending, welding and sawing.

While it is virtually impossible to manually position a part without the use of a clamp, many engineers still experiment with different types of clamp to provide an important fastening mechanism on the assembly line. “Stepped clamps, swing clamps, clamping hooks, variable and pneumatic clamps are all useful components, and all satisfy different applications,” he states. “For example, a variable toggle clamp is often used when an operator has to fasten a lot of workpieces with a different height, quickly and reliably, whilst a toggle clamp is better suited to applications where continuous clamping adjustment is required, with an almost identical clamping force for different cycles. Key to the toggle clamp’s improved consistency over variable clamps is the ease at which they can be used for repeated operation, with a pivot mechanism being created as soon as the handle is actuated. This ensures simple and reliable fastening when pressure is exerted, made possible through the toggle clamp’s unique ergonomic design.”

A toggle clamp needs to be operated with very little exertion or force to allow for fast, repeated fastening, without the operator having to over-extend the force applied. Manufacturing these products with ergonomically designed handles can make attachment and re-attachment easy, but, for this ease to be repeatable, the toggle clamp needs to offer high clamping forces. To guarantee locking and self-restriction when the dead centre position of the clamp is exceeded, leading manufacturers of toggle clamps design their products according to the knee lever principle. This calculates the maximum counterforce required to create a secure hold, with very little expenditure.

“The best analogy to explain how this principle works is by analysing the force required for a person to move a heavy piece of furniture when supported against a wall,” explains Mulvey. “If the person has completely bent their knees and attempts to move the furniture with just the strength of their legs, this is associated with the expenditure of considerable force. However, if the person relaxes their legs with their knees bent only slightly, and presses on the knee joint from above, the furniture becomes much easier to move. As soon as their knees are straightened, and the furniture has been moved with maximum force, it is no longer possible for the furniture to be pressed back by a counterforce.

“This principle has become widely associated with toggle clamps, which work on the same theory. This controllable clamping force that the knee lever principle creates makes these components an optimal solution in drilling, welding, grinding and inspection fixtures. In the timber industry, in particular, extreme deformations can be avoided by using toggle clamps when bonding or building fragile sheets.”

Like many components, toggle clamps can be powered through a variety of sources, including via pneumatics, hydraulics, and electricity. But perhaps the most common is the manually actuated toggle clamp. “This is largely a consequence of the low cost of purchasing a manual toggle clamp, but these savings can cause operators to overlook the overall cost of clamp ownership,” he adds. “Often, low-cost driven companies do not consider the likelihood of downtime or the need to replace poor quality clamps. The overall lifecycle of norelem’s latest generation of toggle clamps, which come with ergonomic handles, is typically around 300,000 clamping cycles and it can be easy to see when the clamp bushes start to become worn – a sign that the entire clamp needs to be replaced.”

Assembly line operators are advised to specify toggle clamps that are manufactured with high-grade, durable materials such as steel or stainless steel. Sourcing toggle clamp replacements from a standard parts supplier such as norelem can also ensure that replacement parts are delivered instantly, reducing the risk of downtime and enabling engineers to get on with the more pressing requirements of their day-to-day duties.

“As the manufacturing industry moves closer to Industry 4.0, the focus is increasingly on automation and connection, as many engineers upgrade their systems and machinery in favour of more cutting edge designs,” Mulvey concludes. “One component that requires no upgrade, however, is the humble toggle clamp, a fixture which owes much to its simple design and functionality. The effortless fastening that toggle clamps create with minimal force has made this standard component a mainstay of industry for decades; and even as the manufacturing sector enters a new, automated era, the design brilliance of the toggle clamp means it will continue to be a permanent fixture on any assembly line.”