It took me a long time to figure out the best way to stop derailment issues on my layouts. Because I use N gauge trains and track which is quite small and tricky the problem may be exaggerated but these rules apply to all gauges. I would fix one section of the track one day and the very next day I would get a derailment on a different section. This is frustrating because it make you nervous about the rest of the layout.
When trains run smoothly on the rails you feel really good about the layout. When a model train derails it can be a nightmare but it is actually quite easy to put right with a little attention to detail.
So my 8 ways to curing your model train derailments are:
1 - Ensure every joint on your track is level, aligned and properly fitted.
This is the most common fault and often is difficult to spot but it is a critical issue.
Keep the gap between rails to an absolute minimum, if you can feel the joint when you run your finger over it you have probably found the problem. If you are seeking security solder the joints because this stops any problems with opening and closing of the joints caused by temperature change or layout flexing. Clean up the soldered joint with a needle file. Just like the real thing, this creates a continuous track.
2 - Check your track gauge on joints, turnouts and frog assemblies.
Constant use and wear to the track components has the effect of either squeezing or opening the gauge. This is common but more pronounced on small gauge layouts. If you install the moving track sections accurately and securely you should have no problems.
3 - Check the rail end at the switch points.
Some new switch points can be fairly blunt on the movable section where it strikes up against the stock rails. This can grab on the wheels and cause a model train derailment. A needle file should be used to smooth the moveable part of the points to allow a smooth transition. Make sure the gauge is identical in the open and closed positions.