Adam Cro discusses how he turned a hobby into a business that blends traditional and modern engineering practices – Matt Pulzer reports.
It’s not every day you meet a 25-year-old engineer with 17 years of experience under his belt. But then Adam Cro and his model engineering company Cro Fittings are neither your average engineer nor business.
Model engineering, the art and science of creating working engineering miniatures (see box below) runs in his family – both his father and grandfather were talented model engineers, as confirmed by a well-stocked, glass-fronted cabinet of beautiful locomotives, and Adam caught the bug when he was just eight.
By day he is a degree-educated design engineer for a company involved in fire hazard test systems. In his spare time, he is the owner-founder, chief mechanical engineer, sales rep and bottlewasher for Cro Fittings.
He manufactures and sells super-detailed parts for model engineers constructing coal-powered, British steam locomotive models. I met him on his factory shop floor – a small room next to his parent’s kitchen – to find out how he runs his miniature engineering company.
This article first appeared in the October issue of The Manufacturer magazine. To subscribe, please click here.
I can see an array of very small bronze components on your workbench – what are they and how are they made?
AC: You are looking at scale, mostly working, fittings of original parts for 1950s-vintage British Rail steam locomotives. That black pedestal includes items such as a fully operating vacuum-breaker blower valve.
The manufacturing is quite complicated. You could summarise my approach as a mix of ‘old fashioned’ and 21st-century engineering techniques. On the one hand, I like to use traditional lathe and mill work, and given the nature of the parts (and customer base) everything is in imperial measurements.
But on the other hand, I use CAD, additive printing and outsource via the web some aspects of fabrication to countries as far afield as New Zealand. Plus, of course, I can promote my business via social media and assorted online fora.
It’s a nice blend of old and new, which is a pretty good reflection of the product and market in which I operate.
So, talk me through your production system.
Once I’ve chosen the part I want to make I do my research. I prefer to work from original engineering drawings (for example from the National Railway Museum archive in York).
However, if I can’t find drawings then I will take measurements from an actual loco – that pedestal comes from Camelot at the nearby Bluebell heritage railway.
Next, I model the part in 3D CAD – the kind of system any modern, professional engineer uses. I start off drawing 1:1, in other words full size, attempting to make a perfect virtual replica.
In fact, I have had inquiries about manufacturing full-size parts, but for now I am happy focusing on miniatures. Next, I scale down the CAD model, typically in the ratio 11.3:1 for 5-inch gauge (the distance between rails) – one of the most popular sizes used by model engineers.
At this stage, I have to do some finessing of the part, particularly if it is designed to operate and not just look pretty. The thermodynamics and fluid flow of a system do not scale proportionally with a part’s reduction in size, so I need to keep an eye on what works and what needs tweaking.
Plus, more mundane aspects of construction such as wall thickness need to be watched carefully because a part may simply be too delicate if scaled without consideration for final dimensions, machinability and operating conditions.
Fortunately, modern CAD is very helpful here – for example, I can set minimum wall thicknesses and ensure there is enough material to produce a viable part. Then there are standard engineering matters to consider, for example leaving enough extra metal on port faces to ensure I can hold and machine them properly. It’s a long list of things that need to be right and CAD is definitely a huge help.
So, now that you’ve got your virtual piece finessed and finished; is this where additive printing comes in?
Almost. I now have to think about where to attach sprues for molten metal flow, and last, but not least – as anyone involved with casting will tell you – it is vital to take account of shrinkage as the liquid bronze cools and solidifies.
Now it’s time to print. I have a partner/supplier/colleague in New Zealand – Mike Jack who has invested in some very high-quality tools, and we cooperate on the additive printing side.
We share a Dropbox folder, so all I have to do is send him the completed CAD files and he can print them off for me on his industrial-grade 3D Systems wax printer. Next, the part is UV cured and we’re ready for casting.
By good fortune, Mike has access to several nearby precious-metal jewellery foundries. They are just the right kind of partner for understanding the kind of fine quality work we want – we simply substitute silicon bronze for gold and platinum.
They operate a vacuum lost wax process, which is how we achieve the superb resolution of the castings. If you look at some of these parts, the original maker’s text cast into the parts has been reproduced in my models, and you need a magnifying glass to read it.
That is the level of quality our combination of modern additive printing and the ancient lost wax process can achieve. And then, finally, the castings are posted to me. I should point out that New Zealand is not my only source of castings.
Depending on the size and cost of parts I also use suppliers in the Netherlands and here in the UK, but my main subcontractor is Mike.
Now that you have your castings, what happens next?
I essentially offer two kinds of products. A machined and finished part ready to be plumbed into a locomotive, or a small bag of castings, material and fixings that model engineers can complete themselves.
I advertise on Facebook, have my own website and have an active presence on model engineering forums where I get the chance to meet customers and present a human face to the company.
Most of my sales are in the UK, but I have sold parts to Australia, South Africa, New Zealand, Spain and Switzerland. Plus, I’ve just had contacts and inquiries from the US.
What’s the future for Cro Fittings?
Although I am happy with the current level of business – and in fact have just about reached the limit of what time permits me to do – there are always new parts to model. I’m also interested in taking on custom jobs outside of the hobby and expanding into other areas.
I keep an eye on the falling cost and rising quality of additive printers, so I am may well try my hand at making my own waxes. It may even be possible one day to go directly to metal additive printing, but that is certainly a good few years down the line – it’s still a very expensive process and the price would have to come down considerably – but time is on my side, we’ll see!
Engineering in miniature
Model engineering is not simply model making, where appearance is the be all and end all. For model engineers, function is just as important as form – in other words, the model has to work.
Model engineers choose a full-sized steam engine (it is usually, but not exclusively steam) and produce an operational miniature version – for example, a locomotive, traction engine or beam engine. Constructors take pride in making as many parts as possible themselves and aim to make them operate just like the full-sized version.
Everything from coal-powered boilers running at (a slightly terrifying) 100PSI to pistons, valves, injectors and steam brakes… literally, all the bells and whistles.
Most parts are machined on lathes and mills from bought-in rough castings or metal stock, and a good locomotive can take five to 20 years to finish. Quality is everything, and one constructor (a former Rolls-Royce engineer) took two years ‘just’ to paint his locomotive to a standard he felt was good enough.
Some parts are particularly fiddly and there is a flourishing market for SMEs to supply items that model engineers choose to buy in to save time or because they acknowledge that some pieces are beyond their engineering capabilities and it’s better to outsource than to struggle endlessly on a few tricky components.
This is precisely where Cro Fittings enters the picture, supplying precision miniature parts to locomotive constructors. From the broader perspective of British manufacturing, the story of model engineering has very much mirrored that of the full-sized sector.
In fact, model engineering first started in Britain at the end of the nineteenth century when it was still a world-leading metal basher, drawing in adherents from the large pool of highly trained engineers, technicians and tool makers.
As British engineering contracted, so too did the number of model engineers, and today there is a commonly heard concern within the hobby that not enough young people are involved – a worry that will sound very familiar to the rest of the engineering community.
Now, just as the manufacturing sector is recognising the importance of attracting the next generation of engineers and investing in techniques such as additive printing, model engineering is also starting to adapt itself and use more up-to date manufacturing techniques, which may well help to attract younger, more computer oriented modellers. To some extent the two rise and fall together.
Full-scale engineering supports and underpins much of what modellers achieve, but just like Adam, young people brought up in the model engineering world learn very early what a fascinating and attractive career engineering offers, and are a ready source of new entrants to manufacturing. In other words, it’s a great way to ‘catch ‘em young’.