A case for bolted-together fire trucks
Bolted construction may have had a bad rap in years past, but precision technology has made it a viable way to build fire trucks
Fire apparatus designers and manufacturers are constantly in pursuit of several goals when constructing vehicles for the fire service. There are five basic goals.
Manufacturers want to keep them lightweight so the truck can carry the necessary equipment and get the best fuel mileage possible. They want to make it durable so that the customer gets the maximum lifecycle out of the vehicle.
They also want to make it cost-effective, easy to repair, and easy to modify so that it can fill several roles over its lifecycle.
Increasingly, fire apparatus manufacturers and their customers are using bolted construction to better achieve those goals.
Bolted construction for fire apparatus is not new; manufacturers like American La France began bolting or riveting vehicle components on fire apparatus in the 1920s.
Through the ensuing years, many criticized this construction method for lacking accuracy and exactness of the parts used.
Such arguments may have had merit prior to the 1970s before new technologies were born that improved the fabricator's ability to measure, cut, and drill vehicle components. Bolting construction techniques have greatly expanded with the introduction of computer-aided design systems (CADS) laser cutters and computer numerical control (CNC).
What is CNC?
McGraw-Hill's Dictionary of Scientific and Technical Terms defines CNC as, "A control system in which numerical values corresponding to desired tool or control positions are generated by a computer. Also known as computational numerical control; soft-wired numerical control; stored-program numerical control."
Today, manufacturers use CADS to design fire apparatus from the ground up. As the designer uses CADS to construct the virtual fire apparatus, CADS employs CNC to create a mathematical action plan to be used throughout the construction process from cutting the materials, drilling holes, and assembling the component parts into the finished fire apparatus.
The action plan
When the action plan is completed, fabricators then feed the data into computer guided laser cutters that precisely cut each part according to very exact specifications and tolerances. The same data is used to ensure that all holes are cut in the appropriate location and that individual hole locations match up precisely with required partner components.
If you've ever assembled pre-fabricated furniture you've experienced this first-hand; it's why the hole for the number 8 screw is always in the right spot.
Whereas a dozen or more workers may have been required to work several days to measure, cut, and drill vehicle parts prior to 1970, the use of CADS, laser cutters, and CNC greatly reduces the overall construction time and the amount of staff employed in the process. Now the process may only take half the time and less than half the previous number of workers.
Bolted construction enables the designer to more efficiently and effectively use materials in the construction of fire apparatus. For example, bolted construction allows the fabricator to use a lighter-gauge metal for a non-structural component such as the back wall of a compartment where strength and rigidity is not critical. This keeps the overall vehicle weight down.
Bolted construction also provides the fabricator with the option of mixing components of differing materials — like metal components with composite components — as another means of reducing the overall weight of the finished apparatus.
Replacement parts are manufactured using the same action plan generated by CADS, so when replacements are needed they fit precisely with the original manufactured parts.
This greatly reduces the amount of time that a piece of apparatus must be out of service to replace a damaged component. It also keeps the cost of replacement parts lower because there's less cost involved in making replacement components.
Bolted construction, particularly when combined with modular construction (they're not synonymous), can provide the end-user with the option of modifying the role of a piece of fire apparatus during its lifecycle. For example, a pumper may be refurbished for second career as a heavy rescue truck.
The improvements in design and fabrication processes brought about by CADS, laser cutting, and CNC have greatly improved the ability of fire apparatus manufacturers to meet their goals and provide fire departments with apparatus that’s more durable, more fuel efficient, and cost-effective.