The right start makes all the difference
Here's a valuable tip for sharpening chisels and plane irons …
Most edged woodworking knives, chisels, irons and cutters have one flat surface that is met by an angled surface to form a sharpened edge. This is true of jointer/planer knives, wood chisels, plane irons, router bits, shaper cutters and more.
The first step in sharpening any of these edges is to flatten the back side before you ever touch the beveled edge. If it isn't flat, you'll never achieve the smooth-cutting edge you desire.
So, how do you know when the edge is perfectly flat ? Simple, before you get started, coat the surface of the flat side that is to be sharpened with a marker….or use tool-maker's dye….then sharpen.
You'll know your surface is flat when all of the marker or dye has been sharpened away.