johnsmachines

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.

1. 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).
2. 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.
3. 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.
4. 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.
5.  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.
6. 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.