V band problems
 

Do you have to smash v bands together the first time you clamp them? Because the v band flange I had welded onto my downpipe and the flange on the back of the turbo don't mate and lock together like the rest of my exhaust even though they are both 3in V Band flanges. Is this a production error or are they supposed to be this way?

Generally use a smear of bearing blue on v bands to see if there's even contact on the whole face post welding. If there isn't, not a good idea to force the clamp as you just end up with exhaust leaks.

I find a bit of paper on a flat surface used in a figure of 8 motion on the affected faces usually cleans them up. Suppose the only thing that would really make it impossible, is large gaps between tube and v band during welding, which would draw and distort the whole shebang.