Primarily determines the rigidity and lifetime of the tooling. The bigger the angle, the longer the knife s lifetime between sharpenings. A large blade angle combined with high quality tooling steel helps in avoiding chipped edges. When the edge of a knife chips, usually caused by cutting into a foreign substance, it leaves a raised streak in the stock after planning. The larger the blade angle, the more material has to be ground off for a particular profile.
More grinding time is involved which is unfavorable for short runs.
Knives used in joint heads are ground with a small blade angle so that more joints can be done with less land left, thus increasing productivity. A dull knife makes itself pull hard, increases vibration and pounding and tends to produce fuzzy grain. Makes sure that only the lead edge of the knife is in contact with the lumber. This allows the metal behind the lead edge to run clear of the lumber. The air flow behind this lead edge on a knife keeps the blade cool while it is in operation thus preventing burn marks.