free form scan of a impeller vane

I have a question on an impeller that, I need to scan the vanes on. i recently learned how to scan not an expert! When i click on free form scan in drop down. you get a window that execution graphics and path definition in tabs. i was told to click on graphics tab... under tab controls click on select. then deselect. then select..... Then go to graphics tab and click on surface that you want to scan across the surface. Then you click on calculate button... it will generate a path and you will end up with a number of points based on the number of hits you want to take per distance traveled per mm.... I get this to work on a couple of vanes but not all of them. example I take 16 points from start area to finish and instead of scan it takes the 16 points that i selected, instead of getting a couple of hundred points scanning. i have scanned stuff before and have had success. as i said some of the vanes will generate a path and will scan. some don't .. so i s there a hole in the model?? or am i doing something incorrect.. thank you