by ACourtney » Sat Apr 07, 2018 5:44 pm
Hi Graham,
Welcome to the forum. Metals always shrink after welding - they expand as the heat is applied and then shrink such that they are shorter than when you started. 6 to 7mm sounds quite a lot though as the usual allowance for steel is 1mm per metre length per weld run, but that might be the difference between hot and cold. Another effect could be if the weld is only applied to one side of a beam/channel section, then it will tend to go banana shaped as it cools (a trick used to get negative camber on live axles is to run weld along the top!).
Alistair