Hi Martin, basically you're making things more difficult by trying to use a very sparse number of points. Now while it's a generally good thing to have a light control point count using a somewhat larger number of evenly spaced points tends to make the specific job of tracing things quite a lot easier. You will still get a light enough point count that it won't be problematic and it is much easier to make the curve very close to your desired shape right from the start. Then go in and do some minimal point adjustment afterwards.

Also while drawing the curve have "Straight snap" on for only first first and last points, either turn it off in the bottom toolbar for the other points or hold down Alt to temporarily suppress it while drawing the in between points. Or leave it off entirely and true up the last 2 points on each side later on with "flat" snap by selecting them and squishing the corner of the edit frame down.

Anyway to draw the curve you follow along your shape placing down points at regular intervals with the points just slightly outside of the shape - the resulting curve will be kind of shrunken down and smoothed from the actual control points so you don't want the points themselves to be directly on the shape except at inflection areas, the points should go slightly outside the shape.

Here's how it looks - notice here how the curve that is created initially is very close to the desired result, rather than trying to start out with some totally different type of shape first:



It tends to be good to this kind of more regular spaced point placement for tracing over something - if you were more freely drawing a shape rather than trying to trace over one you can lighten the point density somewhat. But by having a somewhat higher density than what you were originally trying to do, it helps to limit the influence of an individual control point to a more local area and that tends to make it easier to guide the shape. With a very sparse control point density each point is having a much wider influence over the curve and the points will have to be more expertly placed in highly strategic areas rather than just being able to follow the shape.

The Bezier curve type process is somewhat problematic for CAD because there is a type of implicit segmentation to it - at every node where you have asymmetrical handles coming off the node, the actual shape has a break in curvature at that spot, basically the mathematical smoothness of the curve is kind of interrupted at those areas which is not the case with a NURBS control point curve.

- Michael