If you are like me you keep an eye out for a good deal on used tools. Poorly maintained cutting tools like chisels, planes or knifes can sometimes be bought at a great value because they do not cut. After all what good is a cutting tool that does a poor job of cutting? Many times the cutting edge is rolled and/or has nicks in it. This requires a considerable amount of material to be removed and if you start with too fine of a grit you will find yourself spending a lot of time and still not getting it done.
If you have spent more than 5 min and you are not down to fresh metal across the whole line that you are sharpening then you need to move down to a coarser grit. Many cutting tools have one side flat and you should always start with that side. Resist the urge to tip that side up to shorten the amount of time needed to sharpen it, however that would be a mistake. Tools like chisels and plane irons will not function properly if you don’t keep the back flat.
You want to use something hard and flat for an abrasive. An affordable step many take is to use sandpaper. However it needs to be on something flat. A piece of marble tile that costs a couple of bucks and some spray adhesive works great. If you have a table saw you can also the cast iron part of it to sharpen on with sandpaper.
So the moral of this story is to not be afraid to move down to a courser grit when you come across a badly damaged tool edge. Maybe even down to 80 grit. Look for creating an even scratch pattern across the cutting edge, once you have accomplished that you are ready to move on to finer grits.