Gradients, the curse of railways in whatever scale, how much space can we dedicate to moving a train from one level to another with an incline, scenically it's dead space, and that never appeals. The amount of space or rather track length required will depend on the answers to questions 3 and 4 from part 13 i.e. 3) What type of locomotives do we intend running? 4) How heavy will the trains be? Which in turn are influenced by :- 5) Can you clean the track? 6) How much headroom do you need between levels? 7) How thick is your wallet? So let's look at these in turn. 3) Loco Types My preferred era is British railways steam and green diesel which instantly puts me on the wrong foot for gradients. British outline steam locomotive models are rather low on wheel count when it comes to pickups and traction, maybe 4 or 6 wheels if lucky on older models. Diesels on the other hand, especially recent models may have 8 to 12 wheels powered and all with pickups. Model steam outline locos are less tolerant of gradients than diesels and is especially bad for a helix which I have already decided take up far too much space and could be a nightmare for track cleaning. 4) How heavy will the trains be? With my space constraints, although fairly generous I must admit I need to limit myself to train lengths equivalent to 6 main line coaches. This is as much about fiddle yard, storage roads and marshalling yard lengths as it is about gradients. I will be running vintage and contemporary stock mixed where couplings allow with or without converter wagons. Vintage rolling stock can vary from almost square wheel performance to the very free running British Trix/Liliput stock. Vintage locomotives vary from the heavyweights designed for square wheeled stock, plastic using magnets and light weight 1970s plastic locos using tyres. The industrial branch lines can have tighter curves and steeper gradients as the maximum length of trains will be shorter, e.g. equivalent of 2 to 3 main line coaches with bankers permissible. I need to select my mainline gradients with care. 5) Can you clean the track? Easy to overlook, which may have long term ramifications for spoiling your fun, it is not possible IMO to rely purely on various track cleaning wagons, occasionally you will need to deal with a stubborn problem, e.g. an unfortunate squashed spider or similar. Worse still if a defective point needs repair or replacement. As your faculties diminish this could be a real show stopper. The ability for easy access for maintenance sets the absolute minimum height between baseboard layers. 6) How much headroom do you need between levels? Two aspects to this, minimal for hiding half of the main line (designed as a folded over figure of 8) and maximum for scenic lower levels. So how much do I need, well this will also depend on the depth of the boards, I estimated that I needed about 5 inches to reach across maybe 4 tracks where storage loops were on a lower level. This height must include the thickness of the supporting framework for the upper level and height to install lighting, even if LED strips and for droppers. Access for wiring the droppers to the bus wires is essential during construction anyway, but access to modify later must also be considered and to ensure they are not snagged by my hand or rolling stock. For scenic lower levels more height is required and for that I have aimed as large as possible, nominally between 15 and 17 inches which once again also depends on board depth. To gain this difference I have an incline from the marshalling yard to the upper level and a fall to the lower level. 7) How thick is your wallet? As annoying as always, your wallet has the last say, so keep it happy if not a little strained, there's a long way to go yet before the trains start rolling! Testing Having estimated the heights required it's time to start testing for actual gradients, for this I simply laid some track on a still spare length of timber, placed a representative length freight train on it and a Hornby Dublo Co-Bo, on DC power. I then chocked one end of the wood to different heights and determined how the loco fared as the gradient was increased. Any Dublo enthusiast will quickly recognise that a healthy Co-Bo is maybe the strongest Hornby Dublo made with significant tractive effort available. The theory was that this would set a bench mark as many of the wagons were heavy too. Mainline coaches have far fewer axles in a 6 coach rake compared to the equivalent length of wagons and generally better bearings so it was likely passenger trains would be okay too. Current designs of wagons also run freer than Dublo wagons. After further testing I decided that a nominal 1 in 50 was feasible for the main line and 1 in 30 for the industrial branches. In practice this was modified for the main line to 1 in 48 with the track being level on the curves as much as possible. Subsequent testing on DC confirmed that the main line gradients were acceptable and could be mostly hidden and partly implemented in a cutting on the upper level. Next, the physical layout of the folded 8 main line Jim.