I have tried a few different methods over the last few months to flatten blades. Here is my go-to method for flattening the back of a new blade.
Next comes the 220g w/d. Generally I can get away with using it dry. Again, go for a uniform scratch pattern. I typically try to rotate 90 degrees from the previous pattern, so I know when I have removed all previous scratches.
Onto 400g w/d. Again, remove all previous scratches. I will start to do random motion at this point and lighter pressure once the 220g scratches are worked out. At this point you will begin to pick up a mirror finish.
Going freehand and by this routine doesn’t give as pretty of an edge as going up through 8000g waterstones using an eclipse jig. But you know it is pretty liberating to ditch the training wheels. I have noticed no decline in cut quality or sharpness of the finished blade. This method is also fairly easy to apply to heavily cambered blades, just add a wrist roll to the regime.
At the end of the day I still need more practice. But I am looking forward to the day that I don’t feel attached to a sharpening jig.
-- Doug, woodworking in Alabama