Hi All, New to the forum but not new to building things out of aluminum extrusions... I'm putting together a C-beam machine from the bundle, and I'm noticing that the two 500mm C-beam extrusions are not flat... they rock when I place them on a granite flat - they are twisted along the long axis. I'm worried that when I torque them down to the frame the whole machine will be twisted. Has anyone else come across this? Thanks, Jon.