Most woodworkers know that a shear cut is far better than a straight cut. They also know that a shearing cut produces a superior finish and is much quieter during operation. The helical cutter head addresses each of these through the use of spiral staggered knives that are shear cut. Each individual cutter head is sharpened on four sides allowing for indexing. If you happen to plane a nail or staple, it is not necessary to replace knives the full length of your planer head. Replace the 2 or 3 small knives that were affected and you are ready to get back to work.