Saturday, October 18, 2014

Never Trust a Drawing

Usually I don't tip my hand and show the 3D models I'm designing until I've got at least the first prototype print in front of me. This time though I gave the game away in my previous post so you already know that I'm working on a model of the open wagons used on the Sand Hutton Light Railway so I may as well give you the odd progress update.

As I mentioned before I'm basing the model on the drawings in the RCL Publications book on the railway. The book actually contains two sets of drawings as well as a description of the major components. The first drawing is a copy of the original P & W Maclellan Limited works drawing. While works drawings are nice they tend not to reproduce well in books, especially not when scaled down to fit a single page (all the measurements become difficult to read and obscure the details). Fortunately the second drawing is a modern set produced (I assume) for the book by Roy C Link.

What you can see here is a rendering of the model as it currently stands. There are lots of bits missing, the axle boxes being the most obvious, but it does at least allow you to get a rough idea of the shape of the wagon. If you have seen photos or drawings of these wagons before then the first thing you'll probably notice is that I've had to move the frames outwards to incorporate the larger gauge; the railway used a track gauge of just 18 inches whereas this model is designed to run on 9mm track which is a scale 2 foot 3 inches. From the side this change isn't that obvious although it clearly alters the end on view. The main body is, however, accurately sized, although it doesn't match the modern scale drawings in the book.

Given that the drawings have big copyright statements all over them I'm not going to risk reproducing them here so, unless you have a copy of the book to hand, you'll just have to take my word for what follows. The modern drawings take up the top half of one page and show three views; a side on view, an end on view, and a view from above. Together these give most of the details and those that are missing can easily be gleaned from the copy of the original works drawings. The bottom half of the page is an old photo of a single wagon. The strange thing is that the photo and the drawings don't match! Now I'm not talking about a minor detail like the placement of a bolt or something. No, the main problem is that the planks making up the end walls of the wagons are in the wrong place on the drawing. Now I must admit that it is a fairly easy mistake to make, as I misinterpreted the works drawing initially as well, but when the drawing is placed next to the photo it is obvious. There are other problems, but I think they mostly stem from the fact that all the wagons I've seen in photos so far don't fully match the works drawing.

When I design a model based on a real prototype I strive to make it as accurate as I can although clearly issues of gauge and the available materials force some changes to be made. The point to remember is that while scale drawings are really very useful there is no replacement for looking at the thing you are trying to copy. In this case no wagons remain, but there are plenty of photos that show many of the important details and it is always worth taking a long look at these to see what you might have missed.


  1. Mark, works drawings are rarely,if ever, updated after the first draught and this is as true of Avro Aircraft as the most obscure wagon builder, Ford or Marconi.. I have had to use all the above as a professional modelmaker and every time I ended up using photos far more than the drawings. The only unchanged and perfectly accurate works drawings I've seen were for the Healey 100 and Lola Mk 5 F1 car, but that may not have been a genuine works drawing. Once a product is prototyped and sent of to the toolmakers, it changes, almost inevitably, especially when you often used to see the words "radius to patternmaker", for instance. From that point on, it changes more and more and there is no time or budget or, frankly, need to update drawings that are already tucked away in the archive. I don't even use modern photos of, say, F1 cars as they are usually restored in a most inaccurate way. I have all Motor Sport mags. on disc, so can always be sure to model the piece on lovely old contrasty B&W photos of every race, every year. I therefore insist that when a client mentions a certain car, I ask what year, which race and stick to it like glue. Then, nobody can say us nay. We just flash the photos at 'em with a mental nah-nee-ar-nah.

  2. Mark, never trust works drawings. They are merely a design. The working drawings for pattern makers and machinists are better and if you are ever lucky enough to find a full set will be updated in a box in the bottom right hand or left hand corner.
    I did three years as a detail draughtsman. The worst job I ever had but it got me through Sheffield Poly.
    The views are called projections. Then elevations. Front elevation, right elevation, left elevation and here we go Plan view. I forget what looking from underneath is called. For decorative nuts and bolts you will also find the views you are familiar with, orthographic, perspective and summat else. There were two different projection systems. I will have to look them up as I can't remember. I can remember the artisans opinion of draughtsmen.
    I really enjoy your mastering this modelling.

  3. First and third degree projections, Adrian and Isometric is the other view, that hideous excuse for perspective used by architects in particular, where every view is the same, there is no perspective and tubes look bent or boxes fatter at the back because of it.
    What made me laugh was that as soon as CAD came along all the draughtsmen suddenly became known as engineers! And very few of them were, witnessed by their long winded efforts to design anything that either worked or appeared in under 2 weeks, by which time I will have designed my own version, made it and fitted it! And I ain't no engineer. I am however, a nominated inventor on VW patents. The chief engineer, under whom I notionally worked, is not.

    1. Thanks for that. I knew I couldn't remember or do it when I could. I quite like Isometric You can take sections through it.

      Odds is plan view correct? I lost the plot and joined the Merchant Navy.

  4. Thanks both the names of the views and for confirming that I shouldn't rely on the works drawings. Further work on the model will be mostly from the photos using the drawings for those details I can't find accurately represented elsewhere.

  5. My first thought when I read your post was that surely things like that get altered at the production stage. My second thought was that they probably altered from one wagon to the next. We were not, after all, talking of production lines in those days. It amazes me how many different takes it appears are possible on an essentially very simply piece of equipment. My last thought was "Why am I so fascinated by all this?" I have become strangely addicted to your posts.