after trying one or two other techniques, ive started to model a car in 3d by extruding each of the outlines of the 3 axis, then union-ing the resulting extrusions.

the result is what i wanted visually (top pic), apart from the fact that when i try and convert to poly or sub-d, the edges then "jump out", as though all the edges are unrestrained (bottom pic). ie jagged edges extend from all the edges of the current surfaces. im new (obviously) at this so im guessing there might be several possible solutions .. im hoping i can either stitch the nurb edges together somehow to prevent them going jagged when theyre converted, or get around the whole nurbs stage by just using polys and applying a boolean to those - although ive tried the former, as well as doing booleans to polys and there is either no visible change, or the pieces involved all vanish, i presume there are issues with incomplete overlap or somesuch.

sorry if its already been covered .. half the problem is not knowing what to look for.

anyway, if someone could offer some insight into how to proceed using this sort of technique, as well as any work arounds, id very much appreciate it. im aware of course that there are other tutorials out there for making cars, ie making each piece separately, or making one big poly and tweaking, but id prefer to pursue something along these lines if possible, as i think its quite beneficial to proportions etc to define all the main outer profiles right from the beginning. maybe someone with a lot more experience than me has already come up with a way of doing just that? quite likely ..