The roundhouse kit of parts provided by York Modelmaking contained 13 roof trusses that were cut from 2mm mdf, but having made the decision to replace the two main girders with metal versions I decided to go the whole hog and replace the roof girders. Now I know some will think this to be foolish but I have concluded that the mdf versions are not robust enough to facilitate removal of sections of the roof for display purposes.
the mdf version of girders and trusses
This decision has not been taken lightly as it will involve fabricating 39 seperate trusses - 3 bays each of 13 - and then joining each set with longitudinal roof bracing.
I carried out the necessary research - always an enjoyable task - and produced a drawing of one roof truss. Here are a couple of photos of the interior of the roundhouse showing the best close ups of the roof truss structure I could find.
I produced the following drawing and used it to calculate the quantity of nickel silver and brass I required to make the structure. Rectangular section brass,T section brass, brass tube and nickel silver wire formed the shopping list.
The best way to produce a consistent product is to use a jig so I constructed one on a scrap piece of melamine board using pieces of track ply and made a trial truss.
Some while later I now have three completed trusses.
Each truss is held together as per the prototype using tie bars and clamps which are formed on the model using 1.5mm tube and 0.8mm wire. These dimensions were upgraded from my original choice - used on the trial truss - of 1.2mm and 0.7mm wire. Why you may ask? The 1.2mm tube has a bore of 0.6mm and required enlarging using a 0.7mm drill. I subsequently found a supply of the 1.5mm tube which makes life easier and speeds up assembly and cuts down on the number of broken drills.
Only another 36 to go......................................