Say you want to make 2 or more flat brackets which need to be identical, such as control arm brackets. Rough cut the brackets out of flat stock, then stack them up. Now clamp them together tightly and tack weld them together on the edges, this works best if you can line up 2 sides before welding them together. Now do your drilling and other shaping operations all at once. When completed, break the welds apart and voila! perfect matching brackets.
