— this category includes planes, the regular knives of which are sharpened on both sides. Thus, when working, one side is used, and one is spare, and when the blade is worn on one side, it is enough to turn the knife over and the planer is ready for work again. The disadvantage of this option is the impossibility of sharpening double-sided knives (unlike single-sided ones): when the second side becomes dull, the knife will have to be changed entirely.
