Planning and laying track

General hints

By the time it comes to laying track, you should have a good idea of the route it will follow, either as a detailed drawing or just as a vision in your mind. In either case, it's time to fasten the track to the baseboard. If you are using pre-cut pieces, you can't really go wrong here, provided that some simple rules are followed. If you are using flexible track you need to be more careful. Suggestions follow.

Whether you are using pre-cut or flexible track, adjacent sections must meet perfectly with no kinks or sudden changes of direction. The second-best way to ensure this is to sight along the track. It should be fairly clear if there are any problems. The best way is to run your longest, most troublesome train over the joint at the highest speed you will ever use. Then do it backwards. If it can do this ten times in each direction, and not even wobble, it's probably OK.
It's easy to underestimate the significance of this problem. I have, for instance, a Hornby steam locomotive with a six-wheel tender, that ran perfectly well most of the time, but occasionally would just stop at a random place with its wheels spinning. Eventually it turned out that the middle pair of wheels -- which have no flanges and can move slightly side-to-side -- were being deflected to the side and jamming against the inside of the track. The problem was traced to a small kink in a curve where two tracks joined; on passing this kink it pushed the middle axle of the tender into its fully-sideways position, where it stayed for a while until one of the wheels dropped down and jammed on the track. The defect was hardly visible to the naked eye, and the problem did not even manifest itself at the point of the defect.
You will find as construction progresses that you need to repeat this test on sections of track that get moved by pulling on them. You really don't want to be pulling up track once a load of scenery and buildings are in place, so it's worth being really thorough here.
When using flexible track, it is easy to find gaps developing between adjacent track sections as you work. My approach to this problem is to pull the track through its sleepers with pliers, so that every track end is butted firmly up against its neighbour. Otherwise these gaps will create problems, both electrical and mechanical. A gap of a half-millimetre or so is not a problem, and may be advantageous to allow for expansion. With pre-cut track there should never be a gap of more than half a millimetre if you have assembled it properly (and it is manufactured properly).
When joining track with fishplates, it is easy for the fishplates to fail to engage properly, so that one track end is elevated a millimetre or so above the other. Be careful: this is enough to derail a coach.
Ideally you will have drawn all your curves out on the baseboard before laying any track. A piece of string, a ruler, a pen, and a pin are enough to draw a perfect curve of any radius. At the `experimental' stage you can get a rough idea of the radius of curve that will fit into a particular area by comparing it to the size of circle that would be made by joining flexible track sections. If your flexible track is in 3-foot lengths (it usually is), then a circle made of four sections of this track would have a radius of 23". Another way of looking at this is if you bend a 3-foot length around a right angle, that gives a bend radius of 23" (provided it's smooth). A 23'' radius will accomodate must locomotives and trains. It's a bigger radius than most proprietary pre-cut track systems provide. A circle made of 3 pieces of 3-foot track will have a radius of 17". This is probably as small as you want to go, if you run full-sized tains. This corresponds to making a third of a full turn with a 3-foot section.
Track cannot be layed robustly by relying on the fishplate joints between the sections. It needs to be pinned to the baseboard. You can get short pins from model shops; ordinary half-inch tin tacks may not be useful here, as they are too thick. Pre-cut track sections usually have holes drilled in strategic places for pins. Flexible track usually doesn't: you will need to push the pins through the sleepers and into the baseboard. I find it helpful to hold the pin shank in the jaws of a side cutter, and then push the body of the cutter down and the pin with it.

Working with flexible track

I have already discussed the advantages of working with flexible track: it is cheaper, can follow any curve, and can be cut to any length. However, it does take some practice to work with this stuff, and it's easy to get into a mess.
       The first problem you are likely to encounter is cutting the track. Various possibilities suggest themselves: pliers, hacksaw, bolt cropper, etc. A hacksaw produces a smooth cut surface, but it's tiresome when you have hundreds of cuts to make. Moreover, it's fiddly to keep both rails still while cutting (someone makes a jig for this, which might help). I use a stout pair of side cutters, which cut cleanly but leave a slight burr. Although slight, this burr is large enough to stop the fishplates fitting properly, which is bad. You can file the burr off or, as I do, simply trim the burred area with a smaller cutter. Be warned that even a slight distortion of the cut end will result in the track segments not butting correctly, which will cause problems when running trains later. Another popular method of cutting, which I have not tried, is to use a miniature high speed disc cutter (Dremel make one). This, I am told, cuts quickly and without burring.
       The next problem to overcome is to ensure that the joined track segments make perfect, smooth joins (as described above). I find the best way is to pin the sleepers on each side of the join as soon as possible, then add pins working away from the join. I suggest testing each section with a train as soon as it is connected.
       Don't forget that with flexible track, there's no guarantee that the lengths provided will allow points, etc., to lie in the correct places with respect to one another. Where you have points that work together (e.g., `slips' between parallel tracks) you'll need to mount the points first, then join them with track.

Ballasting

Real track is secured by a heavy layer of gravel ballast. This lies between the sleepers and reduces the tendecy of the track to move when trains pass over it. You can get this effect in a model railway using fine crushed gravel, avaliable from model shops. To simulate sandy areas you can use... er... sand.
There are various well-established techniques for sticking the ballast to the trackbed. One method, which I confess I have not found very effective, is to drip glue onto the area to be ballasted, and then sprinkle the ballast. The problem with this technique is that if you don't get perfectly even coverage first time, it's difficult to adjust, because the glue prevents the ballast being smoothed out. The approach I favour is too poor the ballast all over the required area, smooth it with a small brush, and then poor thinned glue over the top. Hint: about three parts water to one part glue, with a few drops of detergent. The detergent reduces the water surface tension, so the mixture can flow into all the gaps. The photos below show a section of track before and after ballasting. In the `after' photo the glue is still partly wet.

Wiring

If you aren't planning to use DCC for controlling your trains, you will need to take the wiring requirements into account when planning and laying track. Remember that traditional DC control systems work by controlling the track, not the trains. If you have points controlling access to separate sections of track, the normal rule is to apply power to the `feed' end of the points (that's the end that both tracks run to) only. This allows the position of the points to control which track section is live. Beyond this I haven't much to say on the topic: wiring track for DC control is a specialist skill that I haven't had to learn. With DCC control, we simply wire all the track together. The only caveat is to ensure that all the `right hand' rails in the layout are connected to all the other `right hand' rails, and all the `left hands' to the other `left hands'. Otherwise there will be a short circuit across the power unit.
There is one place where this strategy won't work, and that's in a `reversing loop' arrangement. This is one that looks like this:

    /-----\
---/       \
   \       /
    \-----/

and allows a train to enter it and come out facing the other way. If you think about the wiring, the left track on the entry to the loop joins up with the right track on exit, and vice versa. It's an inevitable short circuit. There is an (ugly) way to deal with this in traditional wiring, involve two-way reversing switches. With DCC it goes against the spirit of digital control to use manual switches; happily you can get a gadget that takes care of it automatically. The procedure is to isolate both limbs of the loop from the main track, so that it is electrically separate from it. Then the reversing gadget sits between the main track power and the reversing loop. The gadget switches the polarity of the loop by detecting the brief short-circuit that occurs and the train wheels bridge the isolating links. The gadget is quite expensive (Ł50-100), so you don't want to have too many loops on your layout.