Nah this is not a prob with smoothing groups. You have a six sided polygon because of those edges coming from the chamfer towards the top are ending abruptly. Follow them thru to the bottom of the model and you should be straight.
edit: Actually I'm an idiot and you dont really need those edges, but you do need to fix the circled area. The supporting edges that you have coming up from the + groove should continue at least to the next loop
@yamo, this is what i got when i did what you originally said, will try what you said in your edit (you mean continue it to that very next loop after the bevel right?)
use bevels man and work in all quads. It's the only way to get decent results. The idea is pretty simple. when smoothing out a lowpoly mesh, anywhere that has a quick interpolation between one angle to the other, or a hard angle into a smooth curve you need geometry to support that transition. this image isn't perfect by any means but it does illustrate the point im trying to make. if you are going to smooth an edge you need to reinforce that edge with another that is close to it. If you are going to blend between a smooth and hard surface you need to guide the geometry with extra edges that blend into the curve.
This is a video tutorial off the "how u model dem shapes?" thread, by bitmap, it's modo I think but it's the process that's the point. I found it useful, could be worth a look .
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edit: Actually I'm an idiot and you dont really need those edges, but you do need to fix the circled area. The supporting edges that you have coming up from the + groove should continue at least to the next loop
and that doesnt work either because then it hardens my circle which i was trying to keep
and as suggested use smoothing groups and\or creasing
you keep it clean and chamfer the edges you need "rounded" then turbosmooth.
here's another just for the heck of it
http://boards.polycount.net/showpost.php?p=900468&postcount=281