I spent quite a lot of time fiddling with my designs to inset track, and eventually realised that 3D printed items have slight differences.
Sometimes the code 100 rail slides though first time, but more often than not there is a bit of resistance, better this than it being too loose.
I recommend not trying to force the code 100 rail through, but to get hold of some code 75 rail(N gauge rail might also work), and carefully push this through .
Take care, and take it slowly.
Only when the thinner rail moves easily, try some code 100 rail. Again slow and careful.
Hopefully the result should be rail that sits properly. If if is a bit loose, then I find it tightens up when the base is painted. In fact it can be difficult to remove the rail, so best to delay painting until after the rail is fitted. If you want to spray road markings or something you donít want to get on the rail surface, remove rails, and refit them after painting. (carefully).
Think ahead, and use longer lengths of rail to avoid rail joiners (fishplates).
I have found that bending the rail slightly helps fitting the rail on curved track. The sharper the curve the more this becomes necessary.
Templates are now available to print off, so you can work out your layout design before buying.
A quick note about painting.
No need to use anything oil based, the granular nature of the nylon plastic actually absorbs liquid, so I use ordinary emulsion paint(test pots are cheap), and acrylic paint as I have it anyway. The 3D printed plastic will suck in a lot of paint, especially spray paint.
Simon Dawson (Rue dí…tropal)