HAMMER IT HOME
Dave Skertchly discovers that the hot rivet was a key breakthrough in the industrial revolution, and is deserving of depiction in our models.
Bashing a piece of crude iron or steel to shape and joining it with another piece of steel bashed into shape is an ancient technique. The humble hot rivets that held together Victorian engineering from ships to locomotives, were a technological marvel of the time.
To make the hot rivet work required a new understanding of the metallurgy of steel. Steel is pure iron with a very small amount of carbon in it. In practice, carbon is not added but most of it is burnt out of crude pig iron in the showers of sparks and clouds of foul smoke, which created the Dante’s inferno that later became known as the Black Country. In effect, the remaining carbon molecules stretch, distort and compress the iron crystals, creating mixtures and alloys of
incredible complexity. These alloys vary, not only in accordance with how much carbon there is in the steel but also the way the steel has been heated and then cooled.
We imagine that Engineers such as the iconic Brunel did all this on their own, but in reality, Brunel was the creative focus of an international network of brilliant engineers and scientists who were investigating every aspect of this wonder material.
Steel is special because when it is stretched or squashed in normal use and then released, it returns to its original size; it is why you can make springs from steel whereas brass or aluminium alloy springs are rare. The springy bit is called the Young’s modulus and for steel, the number is high; very high.
A hot rivet is, in fact, a spring. The red hot rivet is bashed into a hole with two steel plates held together with clamps. A head is bashed onto both ends of the rivet, one end with a hammer and the other a bolster. As the rivet cools, it shrinks, a lot, but it cannot get shorter, so a huge tensile stress is induced in the rivet (remember the springy bit, or modulus) clamping the steel sheets. The job of the engineer is to use sums to make that boiler as light as possible. Get the sums wrong and the boiler explodes.
It is quite right that we would want to pay tribute to this wonder of Victorian engineering in our models but alas, much of what we see are not rivets at all, they are a huge range of fasteners based on the nut and bolt, which was mostly developed in the 15th century and famously manufactured in Darlaston in the Midlands, but that, as they say, is another story.
So, rivets and other fittings have become a key feature of our garden railway models, whether as part of a super scale construction or to deceive the eye into believing our models are more detailed than they really are.
The number and fine detail of these fixings have led modellers on a search for the ideal rivet, however, there is just one snag; the common rivet simulations we use as modellers are 1mm or 2mm diameter, which represents 5/8” or 1 1/4” respectively, so somewhat limiting.
One of my early attempts at rivets was to emboss them using a punch from the reverse side of a piece of tinplate, it did not work well but I understand it works better with brass and even plastic card when embossed
against a female rivet shape on the reverse side.
Authenticity isn’t always essential. For knock-ups or stock that may only appear in the background, a few stick-on twinkles applied before painting and then some more details added freehand with a marker pen may well be sufficient. Another of my efforts at reproducing rivets was to make them from cocktail sticks pressed into drilled holes. The cocktail sticks are first pushed into predrilled holes, then cut to length with side cutters and sanded to a consistent length with a Dremel. They are crude but do look the part behind an oversized diesel.
For an example of how it should be done, we need look no further than the Peter Binnie kit of a Glyn Valley Tramway granite wagon, which shows incredible attention to detail with clearly defined rivets, coach bolts and nuts and bolts all in their correct usage. Among my collection is a barn find, a Bandbright skip. It too has well-defined hot rivets moulded into the white metal parts and finer rivets etched into the brass details of the hopper.
So, how do we go about adding those elusive rivets and fastenings to our models? There are two common sources of fastenings; self-adhesive dressmaking twinkles also known as nail art that can be bought from craft suppliers such a Hobby Craft. These “twinkles” are supplied on a plastic backing and can be easily separated from the backing sheet by sliding the scalpel blade under the twinkle, which will then conveniently stick to the scalpel blade while it is positioned on the model.
Specially made moulded rivets and amazingly detailed matching nuts and bolts can be bought from Cambrian models, supplied on a sprue to be cut off and fixed with glue. As supplied, they include a huge assortment of types so best count up the number you require for your project. I counted as few as four plain bolt heads on the sprue.
Cambrian recommends separating the rivets or nuts and bolts from the sprue in a plastic bag to stop them pinging all over the place. I do this is a plastic tray and accept the occasional escapee. I did think of using a vacuum device made from a ground off syringe needle to hold the rivets, a trick learnt from the integrated circuit industry, but in practice, spiking the rivet on the end of a scalpel seems to suffice. Obviously, a significant number of fixings will be upside down in the tray so I just tap the tray and at least half will bounce and turn over ready to be spiked
There is a huge selection of adhesives to choose. For sticking plastic rivets to plastic,
MEK is best but it is hazardous and destroys the ozone layer so use it safely and sparingly. I apply MEK to the rivet/bolt with a small brush when bonding to plastic card. You might want to trim the sprue but it is only by fractions of a millimetre! Alternatively, Humbrol plastic glues use acetone mixed with gum, which is kind of OK. I found that, with patience, acetone (thinners) works well on wood surfaces that have been sealed with model aircraft sanding sealer. I prefer not to use cyanoacrylate for fear of getting it in my eyes but some prefer this especially if fitting rivets to metal.
To place the rivets, you could either research the original or take the practical approach. I fix a rivet at each end of the run, then one in the middle, then one in the middle of that, etc. until I get fed up with it. A light pencil line may help with alignment, but a true eye or a devil may care attitude will probably suffice.
Finishing rivets and fixings, which have been applied to plastic card require only a coat of primer and one of colour. The definition of the rivet is well maintained. For wooden structures, however, I seal the surface with model aircraft sanding sealer and bring the whole thing to a high level of finish. Once dry, the sealed surface is locally activated with thinners. The rivet or nut is then dipped on the surface of a pool of thinners held in a milk bottle top, placed onto the activated surface and held while the solvent evaporates. Wobbling the rivet a tiny bit helps the bond. I then apply a coat of sanding sealer over the rivet or nut to skin over it and help retain it. A coat of primer and two coats of colour finish the job but some definition is lost.
So, as I sit on my rustic park bench outside the Sheep Shearers Arms, I sip at my pint of fine Auld Phagbutt and I’m filled with admiration for those heroic Victorian engineers, but curse them under my breath for the hours I spend reproducing their handiwork in miniature.