There are so many methods for sharpening blades and chisels it can be confusing to know where to start. Sharp tools are a definite necessity when oak timber framing and we all have our own methods of sharpening our chisels, so which is the correct way?
Sharpening is a skill that once learnt, can only be improved with repetition and lots of practice but you must learn to sharpen your own tools. There are a few main principles that you should observe but mainly you are using abrasives to remove metal until you arrive at a keen edge which is where two surfaces meet. The surfaces run parallel to one another until you sharpen one side to make them meet. The abrasives are anything that will remove metal so things such as sandpaper, a grinding wheel or stone will do. The coarser an abrasive the faster it will remove the metal and therefore the finer the abrasive the slower it will remove the metal.
For well used chisels it is important to check if damage requires the metal to be ground away to expose fresh steel. So you begin by squaring the edge. This involves using a square to mark a fresh line on the chisel making sure that the base of your line is below all damaged material. Using a grinding wheel you need to arrange the tool rest so that the edge meets the wheel at roughly 90 degrees.
Have a jar of water nearby, and put the tool in it to cool it off frequently. The tool should never become hot, only warm. You then remove metal to the base of the line you have drawn. The next step is to polish the blade to remove any scratches caused by the grinder. You do this using a stone using direct downward pressure. Do a couple of strokes at a time and check your progress as you go.
Next is to flatten the back of the chisel to achieve a keen edge. Use a lapping stone or flat piece of granite for this. Using a little water and coarse wet-dry sandpaper on it. You start with a coarse paper and move up to a finer grade for final polishing.
We next establish a bevel angle. You would use a coarse stone for this step to roughly shape the edge. You can then refine this using any machine or gadget that you have to create the desired result. Manual abrasives work great here to refine the edge.
And finally you strop the chisel which means polishing the edge. You use a stropping compound with a piece of leather attached to a wooden block and pass the edge over this 40+ times until you are happy with the result.
For a general day to day sharpening you would use the stone to keep your chisels in perfect condition.