Preferred sources for model design –
1. Works general arrangement drawing.
2. Period photographs.
3. Detailed photo survey of a preserved example.
4. Books covering the subject in detail.
The works drawing gives the basic dimensions plus a lot of detail that cannot be easily seen or measured. I like my drawings to be comprehensive – adding the unseen details often gives clues to external detail missing from the works drawings.
Works drawings often have many problems – missing detail, missing structures, inaccuracies, unreadable dimensions, wobbly lines and rather faint are amongst the most obvious. Hence the need for photographs. Often period photos are few and far between.
Sometimes the works drawings are just not available.
In this case a published drawing is the starting point. Even the better published drawings have errors (errors and omissions even manage to creep into the ones I do), and some are just notoriously inaccurate. Most do not provide sufficient detail.
I try to do a full photo survey of preserved examples wherever possible. Sometimes there are no preserved examples – a particular problem with some carriages. Some exist (in various states) but are inaccessible. The photos fill in the detail often missing from the drawings, explain the detail or provide confirmation (or otherwise) that the original drawings were correct. But beware later modifications.
Preserved examples can lay traps for the unwary – the Adams Radial Tank on the Bluebell Railway is one such (see here).
A lot of time and effort goes into researching each prototype when doing the drawings.
Most of the (better) books and drawing sources used to create each model are listed under “References” on the model pages.
Links are also provided there to the relevant Wikipedia page and web pages for any preserved examples.
Generally building an accurate model is no more difficult than building an inaccurate one – it just takes a lot longer to do the initial research.
It also takes some thought and careful design to get everything to fit within the limitations of 1/32 scale – something that some competitors seem to blithely ignore and hope to get away with. If you are looking for a truly accurate model – be careful!