[John Webb]

Dear John,
Welcome to the forum and best wishes with your plans to build a live steam loco. You'll see that there is a section of the forum devoted to the larger scales, garden railways and live steam; it could be worth your while taking a look at some of the posts in that section.

Your driving wheels are 120mm? I query this because 4inches=100mm (1inch=25.4mm to within 0.1%)
The prototype Britannias had driving wheels 6ft 2in in diameter. So to a close approximation your 120mm wheels give a scale of 20mm to the ft. The nearest accepted scale to this is three-quarters of an inch to 1 foot. This is associated with a gauge of 3.5 inches as you thought. (The gauge is the distance between the inside faces of the rails, by the way.)

There have been a number of plans published of this loco at that scale over the years. I can remember 'Practical Mechanics' having a series on building a Britannia soon after they came out in the early 1950s. 'Britannia' herself is preserved at 'The Railway Age' at Crewe.

There are a number of books on building live steam locos - look out for titles by Martin Evens and 'LBSC', although the latter have been published for some time now. Current practice can be found in the 'Model Engineer' and one or two other monthly journals.

You will usually need access to some machine tools. If you don't have a lathe or a vertical drill of your own you will need such items and learn how to use them correctly. Again there are plenty of books available on workshop practices - look at www.camdenmin.co.uk - click on this link and it will take you to the website of Camden Minature Steam Services who publish a wide range of books that should be of interest.

If you were still in the UK I'd urge you to join your local model engineering society where you would receive much help - but I don't know if the French go in for such societies; a bit of internet searching might help.

Hope the above is of help,
Regards,
John webb

 

[John Webb]

Glad to have been of help.

Many owners and Model Engineering clubs don't bother with scale track at this gauge - they tend to use 1" by 0.25" mild steel strip or even angle to form a robust and solid track. Bolts running through tubular spacers hold the 'rails' together at the right spacing. At 3.5 inch gauge you are in the realms of passenger haulage so a raised track taking passenger-carrying cars is very popular. Martin Evan's book "Outdoor Model Railways", published in 1970 by Model and Allied Publications gives considerable detail on various forms of track. It's probably out of print but again adverts in current issues of the "Model Engineer" or the website in my previous post may lead you either to reprints or to modern books on the subject. Adverts should also steer you towards suppliers of materials etc.

I very nearly bought a partly completed 3.5 inch loco off the father of a friend of mine at school in the early 1960s, but the price asked was too high at the time. I did look again at this type of modelling several years ago when I was contemplating returning to railway modelling. Althought I live only a couple of miles from an excellent club track, in the end I went for the Hornby 00 gauge live steamer as this didn't involve the investment in machine tools I would have needed to make. It can also be run indoors all year round.

Regards,
John

 

[John Webb]

Sounds fun! Most 3.5inch locos are designed with coal-firing in mind from the driver/fireman seated behind it. Will you go for gas to give you the remote-control facility? I'll apologise now if I'm telling you something you're already aware of, but do bear in mind that, like the prototype, models of this size need careful warming-up to avoid undue stresses and strains in the boiler which can cause weeping tubes etc..

Regards,
John