3D Printing to aid P2 construction

Since Christmas 2020 the project’s engineering team have been working with WMG to create a one-third scale working model of the cambox for the Lentz-Franklin valve gear. WMG’s SME Team works with companies and organisations for knowledge transfer from academia to industry. Their enthusiasm for the project is helped in no small part by the fact that Dr Paul Lansdell, Innovation Manager and the metallurgist for the metals and materials team was, in a previous role, the Chief Mechanical Engineer at the Dean Forest Railway.

With around 120 parts, the cambox is one of the most complicated assemblies within the locomotive. The Trust has been conscious that before committing to spending thousands of pounds on patterns, castings and machined components, it needed to ensure that the overall concept was functionally correct and that they could manufacture and assemble the many parts of the cambox. The team also wanted to be able to look at variations on profiles of the rollers that actuate the tappets, and in turn actuate the valves, as this was a known problem with the original class P2 No. 2001 Cock o’ the North when completed in 1934.

The parts have been 3D printed in ABS plastic, so they are sturdy enough to test out the mechanisms without the likelihood of damage. The 3D printed cambox will allow the Trust to see if any changes are required to the parts before committing to manufacture. One feature that is not on the production parts is a series of windows that enable the engineering team to see what is happening on the inside.

WMG offered to 3D print a one-third scale cambox and parts for the project. Its capability is unusual in being able to print such large components with high accuracy and robustness. A full size cambox is over three feet long, so the one-third scale part is beyond the capability of anything else the Trust has access to. Even with WMG’s state of the art 3D printers, due to the component’s size, it still took seven days to print the main cambox.

As well as the value of being able to check the functionality and assembly the engineering team has the opportunity to use the cambox model to educate sponsors and donors as well as school parties of the inner workings of Lentz Franklin valve gear. When the locomotive is complete this will be hidden away inside the cylinder cladding, so the 3D printed model will be an invaluable educational aid.  Another part of the service provided by WMG to the Trust is support for metallurgy. Materials and lubrication have progressed significantly since the original class P2 was completed in 1934, and even since the last developments of Franklin valve gear in the USA in the 1940s. The Trust has been able to access the latest thinking on material grades, surface coatings and heat treatment which will give the project an advantage in making reliable and durable valve gear. By embracing modern materials, it enables the Trust to get closer to fulfilling Sir Nigel Gresley’s vision for his ‘Mikados’.

David Elliott, Director of P2 Engineering, The A1 Steam Locomotive Trust, commented, “We are very grateful for the support WMG in helping us to finalise the design of No. 2007 Prince of Wales’ complex Lentz-Franklin valve gear – one of the most challenging aspects of our project to build a new and improved Gresley class P2 ‘Mikado’.”

Mark Allatt, Trustee, The A1 Steam Locomotive Trust, added, “We are delighted with the support the project to build Britain’s most powerful steam locomotive has received since its launch over seven years ago. With over £3.4m spent and around £3.9m donated to-date of the estimated £5m required, we remain on-track for completion within three years. However, to maintain this progress we need to raise £700,000 per year and we are still seeking to ‘P2 for the price of a pint of beer a week’ regular donors or covenantors. We will be launching a fundraising campaign specific to the design and manufacture of the valve gear once the suppliers have been appointed.”