for my daily maya practice i tried to model a bottle cap, which sounds very simple but has some small and interesting details in both polygon and nurbs modelling approaches.
the nurbs way: create a circle which has 8 edit points by default. quadruple the edit points by going into edit curves > insert knot > options: insert locations between selections and 2 at #knots to insert. select every second edit point and scale them to the center a bit so you the circle is now something like a star with rounded edges. select all three curves, then surfaces > loft: now they are lofted together. and now the tricky part: i checked out some ways to cap the open hole on top and most of the ways i found in forums was selecting the outmost isoparm and cap it with make planar. but this method shows a thin seam when rendering which looks very unclean. so here’s a better solution which was explained to me by maya guru greg berridge at vfs: switch to control vertex of component mode and select only (!) the vertex of border of this open hole, then scale them inwards (all axis at the same time) until they nearly come together in the center of the cap. this is best done in orthographic mode. don’t scale until the vertices go into negative values, so there will always be a very, very little hole in the center of the cap, but you won’t see it when rendering the image. check out the result:
the polygon way: create a tube with a subdivisions axis number which dividable by 3 (e.g. 21). go into component mode and select every third lower edge and scale those away from the center along all axis. now add the edge loop on top of the cap and make a small offset edge loop along both sides (to make this edge sharp when adding a subdiv proxy). do the same with the lower edge loop. select all inner faces below the cap and extrude them inwards to move the up afterwards. adjust the transformations and you’re fine by now. it’s quite simple and you even have added ‘weight’ to the model with the extrusion which would still have to be added to the mentioned nurbs model (offset surface and surface fillet the 2 isoparms). here the result for this way:
the one or the other way may be useful depending on what you want to achieve or how you want to use this model.