to correctly model your model: import reference image as a plane. change to ortographic view (press 5 then press 7 with numeric keypad, not the numbers of text keyboard), add a plane, move to where you want to start your draw. Enter edit mode. Select and extrude edges and/or vertices to match the draw (see image, extruding and refining edge position, all faces of new object are quads - 4 edge polygon). when your are done, if will have a projection of your model on a plane, with pure quad-faces. Exit top view, select all your faces, extrude in Z-axis to give depth. Then select vertices where you want them to be at different Z-levels. Select edges to be sharp and increase de "crease" in the transform panel. Perform subdivision surface and add extra loop cuts if needed to constrain geometry. Exit edit mode, Press T, under tool, select shading to smooth.
In the following link, is a Blend file, with one of the blades retopologized by me, you see how I performed a pure quad-mesh, and I do the other blade:https://drive.google.com/file/d/0B7t43CPM6VA-RzFKYVJLSmlkQ1E/view?usp=sharing
In this tutorial, you might see a guy doing a scissor:https://www.youtube.com/watch?v=D8VmGtBebHs
here you see a guy working with reference planes, doing a pure quad-mesh: