It’s some time since I modelled horse drawn vehicles but recent discussion on @Mikkel's blog raised my interest in the subject again. In Janet Russell’s book: ‘Great Western Horse Power’, there is a photograph of the Britzka carriage in which Brunel travelled while surveying the route of his planned Great Western Railway.
This vehicle caught my imagination and the first question it raised was: “what on earth was a Britzka?”. The question led me to research many long-forgotten terms from a lost world of local craftsmanship. According to ‘The Carriage Foundation’ : “A britzschka has the same configuration as a barouche – but whereas a barouche has a canoe-shaped body, the body of a britzschka has a straight, or nearly straight, bottom line and the end panels are either concave or ogee shaped. The earliest britzschkas were suspended on C springs, and under springs were added soon after they were introduced.”
This technical description did not help much, as Brunel clearly had other ideas in most of his design details! A more useful description, given in terms of its function, is currently on 'Wikipedia': “It was constructed as to give space for reclining at night when used on a journey. Its size made it suitable for use as a 19th-century equivalent to a motorhome, as it could be adapted with all manner of conveniences (beds, dressing tables etc.) for the traveller.”
In other words, it served Brunel as a kind of ‘Dormobile’, which must have been very useful to him, since his chosen route for the railway ran through the sparsely populated Vale of the White Horse. I wonder if he ever regretted not following the route of the Great West Road to Bath, with its plentiful coaching inns!
Unfortunately, Brunel’s carriage has not survived, although it can be seen in the background of a photograph of the Swindon carriage shop, 1872, shown in Alan Peck’s book: ‘The Great Western at Swindon Works’. It is thought to have been scrapped during the cull of ‘old relics’, including the original ‘North Star’ and ‘Lord of the Isles’, in 1906.
Road carriages or ‘chariots’, as they were often called, were not popular in earlier years, when the few people who needed to travel preferred to do so on horseback, in view of the general state of the roads. The first carriage designs were similar to farm carts, with an unsprung undercarriage over which the body of the carriage was suspended by a combination of springs and leather straps. I found copious information on choosing and maintaining a carriage, including the costs of the various parts, in a 2-volume work: “A Treatise on Carriages” by Felton, published in 1798. The explanation of the various parts introduced me to a whole new vocabulary of craftsmen’s terms! The bar linking the front and rear axles was called the ‘perch’. - possibly related to the unit of length, which I learned at school : rod, pole, or perch = 5½ yards, although these carriages are shorter than that.
The fore-carriage, which provided the capability for the front axle to turn the carriage, introduced a great selection of terms – ‘splinter bar’ at the front, to which the harnesses of the horses are attached, ‘nunters’ are short strengthening pieces of timber, ‘futchells’ are timbers that link the ‘splinter bar’ at the front to the ‘sway bar’ behind the axle. Many of these parts can be identified in the photo of the fore-carriage of Brunel’s Britzka:
Fore-Carriage of Brunel’s Britzka
A major difference in Brunel's carriage is the absence of a ‘perch’ running the length of the carriage. In Brunel’s version, this longitudinal component terminates in a finial at the back of the fore-carriage, while the rear axle carries the carriage body by means of a pair of three-quarter elliptic springs. These modifications allowed the floor of Brunel’s carriage to be lowered between the axles.
The introduction of turnpike roads and a general improvement in surface maintenance led to very rapid advances in carriage designs during the early part of the 19th century. A major change was the introduction of full-elliptic springs between the axles and the main parts of the fore-carriage. Structural improvements included increasing the use of iron, initially to reinforce wooden parts and later to replace them in many roles. These new methods of construction included the introduction of the ‘fifth wheel’ – a horizontal wheel, which provided a bearing surface to provide much better control of the steering of the front axle.
A Britzka carriage built in 1829 by Adams & Co of London and now in the Shugborough Estate, owned by the National Trust, shows these improvements very clearly:
Fore-carriage of the Shugborough Britzka (1829)
There is a delightful video, extolling the virtues of the Britzka while deploring the depredations of the newfangled railways, on YouTube .
After a long period of research, it was time to consider a model. The complexity of the undergear cannot be represented fully in 4mm scale, so compromises had to be made but I feel it is important to know what is being simplified.
I only had the side-on photograph to work from, so many of the dimensions and details are informed guesses, on my part.
The Carriage Body
I followed my usual method of extruding a 3D ‘body from a ‘canvas’, using ‘Fusion 360’ software. For a reference dimension, I set the diameter of a hind wheel at 4 feet – see footnote.
Extruding my Model Carriage Body
At first, I only extruded half the final width of the carriage. I then added the door and other detailing onto the side before creating a mirror image, to complete the width of the carriage, with the opposite side automatically detailed.
I made the front boot as a separate extrusion to fit against the curved leading edge of the body. Similarly, I extruded the box seat for the coachman from the same ‘canvas’. I created each of these parts as a separate ‘body’, so that they could be printed individually in the optimum orientation.
Once again, I extruded these directly from the ‘canvas’ but I only extruded one spoke and then used the ‘Circular Pattern’ command to create the correct number of spokes for each wheel, in a regular pattern around the hub.
3D-Printed Wheels on Printer Bed
The complete set of wheels took just 4 minutes to print. I also made a spare set of wheels, to replace the very skinny and weak set on my ‘Scale Link’ Horse Bus.
I felt sure that this part was going to be difficult and spent some time planning my way forward.
In order to prepare a plan-view drawing of the fore-carriage, I took a screen-shot of the 3D model of the carriage body and used this to prepare outline sketches in Photoshop. I designed the fore-carriage in two parts – the lower swivelling carriage, carrying springs and wheels, while the upper fixed part is attached to the carriage body. A central pin allows the lower part to rotate about a vertical axis.
Sketch Plan of Fore-Carriage
I imported the above sketch as a ‘canvas’ into ‘Fusion 360’ and used my usual extrusion method to create the upper and lower fore-carriage parts as two separate ‘bodies’, ready to place in the correct alignment with the Carriage body.
My 3D Model Fore-Carriage
For a 4mm scale model, I decided not to attempt to replicate all the complex curves in the prototype but used simple rectangular transoms and other parts. I made an exception for the ‘horn bar’, since the curvature is the reason for its name.
Springs and Axles
I created these as a series of separate components, extruded with reference to the original ‘canvas’ shown above and then manoeuvred into their correct places within the ‘Fusion 360’ model.
The 3D-printed axle trees are a pair of hollow tubes to hold each pair of wheels at the correct distance apart. The wheel bearings will be provided by 1 mm diameter metal rods, passing through the wheel hubs,
The front springs are full-elliptic and were drawn using the ‘3-point arc’ tool, then extruded. They fit between the front axle and the main transom.
The hind springs are three-quarter elliptic, with one end attached to the side of the carriage and the other to a block carried on a bracket attached to the rear of the carriage. A bar links the brackets on the two sides. These parts were drawn with reference to the original ‘canvas’ and then extruded.
On the prototype, the fore carriage was attached to the underside of the front boot by means of an array of iron tubes. I considered using metal wires for my model but then, after making a few modifications, decided to create these supports as an integral part of the 3D-printed fore-carriage.
I extruded a support bar across the width of the underside of the front boot and then made two curved bars between the horn bar and this new bar. I extruded another straight bar from the ‘perch’ at the back of the fore-carriage up to the same support bar.
For the diagonal struts, I used the ‘Sweep’ tool in 'Fusion 360' to extrude from a circular pattern, drawn on the top of the horn bar, then following a diagonal path to the support bar below the boot. For drawing the path, I enabled the ‘3D Sketch’ capability of ‘Fusion 360’ (in the Sketch Palette), which can be rather confusing when viewed on a flat computer screen. I found it best to draw the path approximately first and then make small ‘Move’ adjustments to the end points, while viewing from a couple of orthogonal directions.
My 3D Model of the Front Frame with Struts
As I have mentioned several times, I have kept many of the parts as separate ‘bodies’ so that they can be printed individually, in the optimum orientation for each component. To ensure that all the parts will fit closely, I have moved them together within 'Fusion 360'. The result of this ‘general assembly’ is shown below:
General Assembly of my Model in Fusion 360
The real work when making a 3D-printed model lies in the research, followed by the design of the model within the chosen Computer Aided Design software. In my own case, I have been reading about horse-drawn carriage design since the beginning of this year. Apart from the ‘Treatise on Carriages’ mentioned above, I also learned a lot from a ‘A History of Coaches’ by G.A.Thrupp, 1877, and ‘The Development of Center-Pivoted Fore-Carriages’ bv Dr. Gordon S. Cantle in The Carriage Journal: Vol 26 No 1, Summer 1988. See also 'Carriages and Coaches' by Ralph Straus, 1912.
Since I only had a single photograph of Brunel’s Britzka, I spent a considerable amount of time deciding what details were appropriate for a carriage that was presumably built around 1830.
I then had to break my overall design down into parts that could be printed on my 'Geeetech' E180 FDM printer, with minimal need for additional support structures.
After going through this lengthy period of research and design, the actual printing was simply a matter of loading the files onto a memory card, inserting the card into the printer, and pressing the start button!
For the record, the print times (estimated by the ‘Cura’ slicing software) were:
- Carriage Body: 29 minutes
- Front Boot: 8 minutes
- Box Seat: 7 minutes
- Fore-carriage: (2 parts, printed together): 5 minutes
- Wheels: (4, printed together): 4 minutes
- Springs: (5 parts, printed together): 5 minutes
Once all the parts had been printed, I took the ‘group photo’ shown below:
My Britzka Model Components, as printed.
I am especially pleased with the appearance of the fore-carriage, which I had anticipated might have proved too delicate to print in 4 mm scale:
My 3D-Printed Fore-carriage (2 parts)
I shall pause for breath here. There’s a fair amount of fettling and fitting together of the various parts, then the painting and the addition of details such as carriage lamps. I plan to cover these in a future post
Footnote: since my initial estimate, I have realised that the photo shows the carriage straddling some broad gauge track. Scaling from this track yields a hind wheel diameter of 4' 2" - close to my original estimate.
Edited by MikeOxon