When the 40x40 angle iron was spot welded to the 100x5 flat iron strip, the lengths were very straight. However, after the galvanising process they had developed a slight curve (no doubt due to the heat involved and the way that the lengths (5.5m) were suspended in the liquid zinc). I tried straightening the lengths out by bending them the opposite way but this had no effect. When affixed to the top plate of the wall the curve still remained, so I used an acrow prop to set the wall straight and then fixed the roof bracing to the control room, after which I was able to release the acrow prop with the track remaining straight. This was not a problem with the roll-off section as the tracks were fixed to 100x50 RHS galvanised steel which was strong enough to hold the track straight.