Due to the COVID-19 outbreak, the KSEL team have been quarantined and are working from their home offices, resulting in no travel time and more time available to work on the carriage.
So, instead of chilling on the sun loungers in the garden, armed with endless food and drink (like most people), the Pulborough team took to utilising the extra time by putting on the overalls and plunging back into the carriage restoration.
Although the carriage looks great so far (see previous blog posts for reference) there are a couple of missing details that, once finished, will bring the carriage back to life. With the time we have during this pandemic, we look to complete a series of different projects to finish the railway carriage, so stay tuned for updates on our ongoing projects!
In its current state, the carriage is missing a number of bespoke copper components which would have been included in the original design. These are namely a set of “catches”, loop-shaped internal handles and T-shaped external handles. Fortunately, the carriage already contained one of each of these components from which new parts could be reverse engineered. For this purpose, we have chosen to collaborate with an engineering design duo from Nottingham who go under the title of ‘Tall & Small Designs’.
Our first project is to reverse engineer the copper ‘catches’ which would originally have been used to hold the leather strap, which held open the railway carriage windows. In 1875, the small catch device was screwed into the door frame of the carriage, as shown in Figure 1. An accompanying leather strap with punched holes provided the support for the window. The catch would have fitted through the punched holes in the leather strap and the window could be lowered.
Traditionally these catches would have been made by a skilled engineer who would have turned a copper bar to size before being screwed into the door frame of the carriage. Due to the fact that copper oxidizes rapidly, thus degrading over time, it is extremely rare to own one of these ‘catches’ – especially in as good of a condition as ours. However, the carriage requires 10 catches and we only had 1 original.
Turning a copper bar not only requires a lot of skill and access to a lathe, but working in copper is extremely expensive – especially if you get it wrong! Instead, we opted to employ modern techniques to re-create the copper catches. Using a home-built 3D printer (yes, home built) and a material comprising of a renewable plastic (Poly(lactic acid) or PLA) filled with ~80% fine copper particles, we were able to 3D print replicas – which was much harder than it sounds (trust me).
When selecting the printing material we had 3 choices:
- print from conventional PLA and then paint the components using sprayable paint
- print directly using a copper-coloured PLA
- print using copper filled PLA then sand and polish the parts
In the end we went with option 3, as the copper powder provides some real physical properties of copper metal whilst being more authentic in appearance and weight. It also gave the ability to polish components to a high level of shine, the copper particles also undergo oxidation and hence, a patina effect can be created. This latter feature is not of importance for this project in particular as the catches remain dry and un-weathered inside the carriage, however will come in handy in future work for the exterior handles… so watch this space!
Before we could go about printing the catches, we first had to reverse engineer the design from the one remaining original copper ‘catch’. Using a ruler and a collection of photographs we were able to replicate them as a 3D model in CAE software. The model file was then exported to an open-source 3D printing software called ‘Repetier Host’ where it was converted into G-Code… which is a fancy way of saying 3D printer language.
A number of prototype iterations, as shown in Figure 3, were created from unfilled PLA until we had the perfect dimensions before moving onto the copper-filled PLA. Following a few failed attempts, we eventually got the print parameters and temperatures just right, then it was time to print the final product.
The image below shows the raw 3D printed pieces. As you can see, these are by no means ready to put on display! The 3D printed layers are visible, there are some rough edges and the dull, matte, clay-like finish is not ideal. In order to make these raw pieces carriage-worthy, we needed to sand and polish the them.
Sanding and polishing 9 of these catches would have taken hours if not days and, whilst we may have the time, we certainly did not have the inclination… so instead, being the engineers that we are, we decided to make our lives much easier by designing a jig to attach the printed catches to an electric drill. The jig, shown in Figure 5, enabled the pieces to be spun by the drill, making sanding and polishing a far more efficient process.
With the new jig piece and hand-held drill, the sanding and polishing only took 20 minutes per part! After they were sanded and polished, they were removed from the jig and ready to be fitted using screws and as you can see, they look great!
Life has a really weird way of giving you silver linings – or in our case, copper ones! We hope that all reading this blog are staying safe and healthy during the pandemic, and we look forward to updating you with the next instalment of projects very soon!
