The method described below is not at all suitable for everyday sharpening, which should be done with specialized equipment. But, if you find yourself in a situation when you really have to finish planing something quickly (as it happened to me today, so I was able to do this video), you can use this method to freshen up your planer’s blades.
What you need to keep in mind is:
1. Most probably you’ll fail at your first attempts, so try it with some unusable old blades. It takes time and practice to learn how to keep the grinder and to move it smoothly.
2. Don’t ever use grinding discs, they most probably will damage your knives to an extent from which they can’t be resharpened, even at a specialized shop.
3. Use good quality sanding discs. If you use dull discs, the heat generated will be higher and there is a risk of de-hardening the steel.
4. If the knife has a lot of damage, repeat several quick passes, rather than holding the grinder in one spot too much. It will take you longer, but it will reduce the risk of making the knife wavy.
5. Check regularly if the knife got too hot. I usually know it’s too hot when it becomes difficult to keep my hand on the knife. I then stop and wait for a while and move on when the blade has cooled.
6. As long as your movement from one end to the other is smooth, there is no risk of making the knife wavy. The only place where you’ll damage it is at the beginning of the blade. If you are left handed, as me, this is not good, as the damaged end is right in front of the fence of the planer, so I have to add a piece of wood to the fence to make square edges. If you are right handed, you’ll probably start at the left and move to the right, so you’ll damage the knife at the end far from the fence, so you won’t have problems with jointing boards.
7. The angle is important, but it’s not essential. As long as you maintain the angle in a +/- 5 degrees margin, there won’t be a huge difference in the planer’s performance. This is because the knives are sharpened at an angle that represents a compromise, anyway (the ideal conditions would be having a set of knives for each wood species, as they tend to splinter at different angles).
8. I don’t abuse of this method, and use it only when I can’t go to a professional sharpener, or when the knives are designed so stupid that they can’t be sharpened using their tools (as with the knives of my Metabo DH 330, which are too thin to be held in place in the sharpening jig. Anyway, they are supposed to be disposable, but I usually resharpen them using this method once or twice).
Thanks for reading!