Site Search


The devil is in the detail

In this blog, Graham Shirley, Senior Mechanical Engineer at 3P, talks about his passion for heritage engineering and how the heritage sector can play a major role in training and inspiring tomorrow’s engineers.

A blast from the past

Heritage engineering is something that grips me; we love visiting the past. Having travelled around Europe, I think I can safely say it is something we excel at in the UK. Many engineers will be familiar with the saying ‘The devil is in the detail’. Some heritage centres recreate scenes where actors play characters of the past in their heritage working and living environment. They tell you a story and you can converse with them and explore their thoughts and reasoning for doing things the way they did in the set time period. They may remind some of Eagle comic, Meccano, or a book for Christmas. Some may say their best teacher is their determination to get something done. Being an engineer, it is the detail that drives me. I love to look at old engineering photographs. There is a new invention on display, but what interests me is the tools and parts lying in the background. Why are they there? What were they used for? My visit to a heritage railway centre a few years ago triggered a meeting with a group restoring some 1950’s heritage.

Richard Heenan and Hammerley Froude formed an engineering company in Manchester in 1881. You will know of their best-known creation – Blackpool Tower 1. Before me was another creation, not so widely known, but it had been an exhibit on Heenan & Froude’s stand at the 1951 Festival of Britain exhibition on the South Bank in London, next to the Royal Festival Hall. It was a box of mechanical parts, linkages and cams with two inputs and it generated 4 outputs. An analogue computer, when computers were mechanical devices rather than digital electronic.

The group explained that the original was in the Science Museum, Kensington, London. I had probably seen it when dad took me in the 1970s although its significance did not register with me at the time. The one on display before me as a replacement that the Science Museum had partly funded. It was broken, and most of the people who made the replacement were long departed and the company in Worcester no longer existed 2.

Like clothing fashion styles, engineering products are embellished too.

One part I noticed had a military fashion style. I wondered why. I have seen many ways of clamping a ball bearing in place, usually a clamping ring with an array of bolts around the circumference. This application caught my interest as it looked like a breech lock detail I had seen on large guns. The design had been crafted by three people over a 20 year period, A Caprotti, F J Kuretschka and LT Daniels. Whilst reading an article from the 1980s, I learned people had been impressed and had striking memories of an Austrian U-boat commander Kuretschka 3.

The highly-skilled heritage centre was experienced with heavy forgings and locomotive parts. The analogue computer was a ‘different kettle of fish’, more like a car engine in fashion. It has smaller parts, with precision shapes. The problem presented in a part with a precision shape that had broken, the part being a cam – which is a like a wheel, but rather than being round, it is more pear shaped so the axle height to the road varies as the wheel rotates.

Fortunately, the progress of technology has assisted with the problem of fixing the broken part. Whilst the market for heavy forged components has decreased massively since the 1950s and the procurement of such parts is difficult and very costly today, the analogue computer was made of parts which could be produced much more easily in a modern engineering environment. The integration of digital computers into the manufacturing chain from design through to manufacture has massively reduced the cost of making the complex cam since the 1950s.

How times have changed

Older primary school children may have been exposed to a Raspberry Pi single board computer 4, and teenagers will be more so. It is important to encourage tomorrow’s engineers with STEM activities and expose them to engineering design at an early age. For £120, it is a very powerful engineering tool beyond the dreams of an analogue computer design team in the 1950s, but it in the hands of today’s children can fix the broken part. The Raspberry Pi 4 running the Ubuntu 64-bit operating system enables access to freeware software. If you have a Windows 10 computer, that can be used also and the software installation is easier.

FreeCAD 5 is a solid modelling application similar to Inventor or Solidworks that professional engineers use for design. Children are well aware you impose your creativity upon the world by making a sketch. SMath Studio 6 is powerful mathematical notebook – like word processors but for maths equations. Very handy for your Maths homework as it replaces a calculator and gives a good print layout for your teacher.

So we have the key software tools for design engineers in the hands of budding primary school engineers for free. The details of how to do engineering design with this software is not taught in schools. YouTube is a good resource to help up the learning curve with both packages. There are many examples to start you up the learning curve, creating, making, 3D printing if you like.

The maths for the cam is a little beyond the primary engineer but enjoyment with the software and a creative mind will inspire your learnings further. The shape of the cam is defined by an acceleration, and velocity profile that may be more familiar to Advanced level students. Here is the math:

The techy bit

This gives the height of the axle off the road as the wheel rotates. It shows a dwell, then rise, dwell and fall back to the starting level. This defines the shape of the pear, or cam.

Using some geometry calculations with Sin, Cos and Pythagoras theorem, this is data is wrapped in a ring to form the cam contact wheel axis curve shown in blue. The shape of the cam surface is generated by offsetting the curve by the size of the wheel in contact with the cam – and is shown as the red curve. The green curve is a plain circle to emphasise the shape change. The red curve is exported as an Excel file for transfer to FreeCAD.

The red curve is then imported into FreeCad with the WireXYZ macro 7 to generate a sketch. The pad tool 8 is then used to form a 3-dimensional model of the cam which can be used to make a new part.

What heritage engineering can do for you

If a visit to a heritage activity sparked your engineering interest, do delve into the detail behind the scenes. I often hear the young saying they are struggling to find a job because they lack the experience. Many have found a bridge over the valley of death between study and industry in heritage. The heritage sector can play a major role in training and inspiring tomorrow’s engineers as it allows engineering activities to be experienced where the usual company requirements of product confidentiality are removed.

It is often difficult to connect with the right people on your visit initially as engineers are rarely front-of-house, but if you express your interests, the skills you want to learn and develop, send a few emails and you are on the way to making the right connection. Covid has super charged video communication. Now you can join a team and be mentored by experienced people without stepping outside your front door. At 3P, we know engineers enable change in society. 

Tomorrow’s engineers have never had it so good.





3 Duke of Gloucester publication newsletter A9. Caprotti Poppet Valve Gear – Engines, People & Company Part 2. Hugh Phillips.






For Windows 10

  • Install FreeCad from website
  • Install SMath Studio Desktop from website.

For Raspberry Pi 4 with 4 or 8GB memory

Set up a new SD card with Ubuntu using the Raspberry Pi Imager to download and install ubuntu. I have used version 20.04.

Freecad Install

I have version 18.4 working. Version 19 is available but not working at time of writing on the Raspberrypi 4.

In a terminal window type :

sudo apt-get  update

sudo apt-get upgrade

sudo apt-get install freecad freecad-doc

sudo apt-get  install python3-pip

pip install GitPython


To use 3D connexion SpaceMouse Compact with raspberrypi is you have one:

sudo apt-get install spacenavd libspnav-dev

Every time you boot to enable the Spacemount working in freecad in the terminal window the lines below before using freecad.

sudo /etc/init.d/spacenavd stop

sudo spacenavd -d

some of you will be clever enough to add this to the startup.

See freecad spacemouse help and set up buttons on the tools customise menu selection in freecad. Press the spacemouse button first to see the menu options in the menu.

SMath Studio

On the Raspberry Pi, you will need to download the SMath Studio Desktop for Mono. I have used build 7610 from 1/11/20.  Extract the file, right click for the option. To run the code, simply double click on the .exe file, but before this works you will need to install the Mono. Mono is a cross platform open source.NET framework. You do this with:

sudo apt- get update

sudo apt-get install mono-complete


Sign up for blog posts