Historic Model Compromised?
I was attempting to model the Trevithick Dredger Engine as true as possible to the original. But, I also wanted it to run, so the flywheel would spin and the crosshead move up and down and the unusual valve control lever flick up and down.
There are several problems with this approach.
- The 1 in 8 scale. This is the biggest problem with making a model. Since the scale applies only to linear dimensions (e.g. the boiler is 6″ diameter compared to 48″ for the original), surface areas are at a scale of 1 in 8×8 (1:64) and volumes and weights are at a scale of 1 in 8x8x8 (1:512). So my little model weighs a few kilograms (not actually weighed it yet) compared to 4 -6 tons for the original. It does mean that there is a safety advantage in scaling down, in terms of boiler explosion risk, despite the fact that the model will be run at roughly the same boiler pressure as the original (50 psi).
- Some components do not scale well. For example, the square nuts. To my eye, they look too big. If I was to make another of this model, I would make the fasteners smaller.
- The requirement of the model actually running. The original was fired with coal, or in some situations wood, and even dried animal dung (in Peru, look it up. There was no coal and no trees in the silver mines area). I have made my model so that it could run on coal, but to be honest, that is unlikely to happen. So I have made a gas burner. And that involves gas pipes and regulator valve, which are impossible to conceal, and detract, IMO, from the appearance.
- Boiler regulations. I want to run the model at club exhibitions, which means that the boiler must be certified. The boiler certification regulations make no special allowance for historic models, so several compromises have been made. For example a pressure gauge has been installed, and the water level taps must be replaced by a glass sight tube. Not a biggie I guess, but it all adds up. I will keep a separate set of parts which can be used when it is displayed as a static model, which will be most of the time.
- Is this a model dredger engine or a model factory or mine engine? I still have not decided. Hence the rather ambiguous base. I do not intend to build a dredger or section of a dredger, or a factory or mine or parts thereof. But I have to admit that the base which is appearing in the photos so far does not look “right”. Still pondering that one.
- And finally the colours. Although Trevithick was a brilliant engineer, he was no artist. I doubt that beauty, or attractiveness of line, ever entered his thoughts when he was designing. If his engines were painted, the colour was probably utilitarian black. Not that we know. I can find no reference to colour in any of the works about Trevithick and his engines. And there is not a skerrick of original paint on the original engine in the London Science Museum, as far as I know. Later engines, in the Victorian era, were painted in gorgeous colours, and I am tempted to paint my model as if it were a Trevithick engine which was being used in the Victorian era. That is not so silly. It is known that Watt engines, and even Newcomen engines were still being made in the 19th century, and Francis Trevithick records that many of his father’s engines were in use in the mid 19th century. That little subterfuge could also explain why my model has a pressure gauge and sight glass!
I had a full day in the workshop yesterday, so I had better front up and straighten those steps for SWMBO. Actually, it will an interesting job. I will use a 4WD high lift jack(s) under the house to free the steps, then use the Landcruiser winch with a snatch block to pull the concrete steps into position. Might be worth a photo. How the steps ended up out of position is a mystery.
I think you worry unduly about the compromises. You models will, I imagine, be viewed by two types of spectators, the uninformed who will be impressed anyway and won’t even notice any variations, and other hobbyists who will understand them.
Since nobody knows the original colours just paint it whatever looks prettiest, who will be able to prove you wrong? 🙂
Thanks Ron. that is what I intend
Only you and Joe Pedant will notice fasteners et al.
What the rest of us will see is a fascinating and historic Trevithic engine running on steam!! What a thrill.
These don’t grow on trees. It warrants a celebration never an apology.
FWIW I’ve changed to my second option re the base.
Instead of #2 (bricks), I’m back to a simple wooden block ( not too dark) eg Tasty oak or even Huon pine so that the star of the show shines. ( full of opinions today)
With that I’ll have lunch, good luck with the steps.
Good on you Tim. That is very encouraging!
1 I’m interested in how much energy is needed to drive the model and how it scales up/down from the original. Does a 1/8 scale model use 1/8 as much power to run?
2 Are hexagonal nuts out of the question? Or octagonal?
3 If you fed the gas from below it would be unobtrusive, hidden by the wooden base for the most part or incorporated into it.
4 Pressure gauge and water sight tube make it all the more interesting, safe and useful in teaching about steam power.
5 You’ve always called it a dredger engine; oak framing is appropriate but it needs some finessing.
6 Black, brass, copper, steel, oak look pretty good on a working engine. I don’t think it need be pimped out in a Victorian color scheme.
Hi Richard, I am pleased that at least one person read and thought about my musings on the subject of scale. As for scaling energy, I really do not know. I do know that model engineers usually do not concern themselves with energy efficiency. An interesting question. I will give it some thought.
2. Nuts and threads were hand made in 1803. I believe that they were all square. Cannot give a date when they went hex.
3. I would liked to have fed the gas from below, to hide the tubing, valves etc. but that would have made the conversion to coal firing more problematic and difficult.
6. still thinking about this one!
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