For more than six decades, Boro Foundry Ltd. has specialized in ferrous castings from 0.5 to 6.5 tonnes, offering full in-house machining for complex, short-run projects across sectors such as steam locomotive restoration, waste-to-energy, and heritage components.
When tasked with producing a new cylinder casting for a historic steam locomotive, the team faced typical legacy challenges: complex geometry, one-off production, and no existing tooling. The right-hand cylinder had already failed in service—making a precise, durable replacement essential.
Powering the heart of the locomotive
In a steam locomotive, the cylinder is the beating heart of the engine. It’s here that steam from the boiler expands, driving the pistons and converting thermal energy into mechanical motion that powers the wheels. Each locomotive typically features left and right-hand cylinders, which must be manufactured to exact tolerances to ensure synchronized operation and long-term reliability.
“The cylinder is the component that produces all the power,” explains Sam Edwards, Director for Sales and Business Development at Boro Foundry. “It distributes steam between chambers, forcing the connecting rods to drive the wheels. Precision is everything – any defect can affect the performance of the entire locomotive.”
Why 3D printing was the obvious choice
Creating a traditional wooden or polystyrene pattern for such a complex one-off cylinder would have been prohibitively expensive and time-consuming. Its intricate internal geometry with multiple cavities and thin wall sections added risk of distortion and assembly errors. Instead, Boro Foundry turned to 3D sand printing using voxeljet’s binder jetting technology, a process they had used successfully for smaller cores for over a decade.
The parts were produced through voxeljet’s On Demand Printing Service in Germany, ensuring precision and significant time and cost savings. Employing FDB (Furan Direct Binding), seven silica sand parts ranging from 650 × 380 × 340 mm to 1424 × 1150 × 530 mm, which combined into a single 1424 × 1150 × 919 mm mold were produced and delivered ready for casting.
3D printing gave us confidence in accuracy and repeatability that would be very hard to achieve with manual pattern making.
Sam EdwardsDirector for Sales and Business Development at Boro Foundry
Simplifying complexity through digital manufacturing
Through close collaboration between Boro Foundry’s engineering team and voxeljet’s experts, the mold assembly was optimized digitally before printing began. This enabled clear visualization of how each section would fit and how cores would align—reducing the risk of mismatch or deformation during casting.
“Through CAD design, we were able to discuss and plan mold assembly in advance of production,” says Edwards. “That ensured a smooth workflow and minimized risks. 3D printing gave us confidence in accuracy and repeatability that would be very hard to achieve with manual pattern making.”
Using their induction melting process, Boro Foundry poured cast iron with a small addition of phosphorus at the precise temperature needed to achieve the right balance of strength and machinability. The finished castings were shot-blasted and machined directly at Boro’s facility to ensure perfect fit and finish.
Overcoming casting challenges
One of the biggest technical hurdles was the thin wall sections, just 38 mm thick, which were prone to veining—a surface defect caused by sand expansion during casting. To address this, Boro Foundry developed a special coating technique that prevented the formation of veins in the internal cavities, preserving the part’s dimensional accuracy and surface quality.
“The internal sections were particularly challenging,” notes Edwards. “But by adjusting our coating process, we managed to eliminate veining almost completely. It was a learning experience that improved our overall foundry know-how.”
The results: precision, cost savings, and flexibility
Thanks to voxeljet’s 3D printing, Boro Foundry achieved remarkable results:
- 100% cost savings compared to traditional pattern-making methods
- 50% reduction in lead time from concept to finished casting
- Significant accuracy improvements that minimized post-processing and rework
“The savings are substantial, but the biggest benefit is flexibility,” says Edwards. “We can take on complex, one-off heritage projects without the burden of pattern costs or long lead times. It gives us and our customers real freedom.”
For heritage railway operators, this speed and precision mean less downtime and more reliable preservation of historic assets.
A future shaped by 3D printing
For Boro Foundry, additive manufacturing has become a strategic tool for modern foundry work, offering clear advantages for bespoke and intricate castings such as those found in steam locomotive restoration. While traditional methods remain relevant, 3D printing enables the efficient production of large, complex one-off parts with exceptional accuracy. Looking ahead, the foundry hopes for larger, faster, and more sustainable printers that allow sand reuse without compromising quality. Above all, Boro Foundry values voxeljet’s consistent quality and support—proof that modern technology can help preserve historic engineering.
