Sometimes it is more practical to weld sub-assemblies before the final assembly. Parts for a scissor lift include requirements to align parts bore to bore. Special alignment shafts to match the bores are located in the fixture with v-blocks. As an interesting aside, scissor lifts are also used with our tables to compensate for tall and short welders as well as dealing with tall and short parts.  For the longer final assembly, angles are mounted to the sides of the table as outriggers.