At the point where the 45mm and 64mm gauge part ways, this point was causing derailments. So on the bench it went for some "tender loving care".
Naturally, the coursest file I have is an excellent vehicle for tender loving care.
The culprit is the bit that the green arrow is pointing at. Undergauge 45mm wheelsets will derail when pushed into it.
After reshaping it, I also needed to make sure it's as far from the curved through rail as it can be. The brown plastic podest that holds it has too much play.
So I made a wedge from some plastic offcut of a similar colour, and secured it with epoxy.
Now every kind of wheelset runs past smoothly.
