The Planer Knife Mark Calculator estimates the cutting pattern left on a planed surface using cutter head diameter, number of knives, head RPM and feed speed. It supports Imperial and Metric units and converts the inputs when switching between them.

• Increasing feed speed increases feed per knife and scallop depth while reducing the number of knife marks per unit of length. Increasing head RPM or the number of knives produces more closely spaced cuts and reduces the calculated scallop depth. Increasing cutter head diameter also reduces scallop depth without changing knife mark spacing.
• For example, a 14.125-inch cutter head with 24 knives operating at 3,600 RPM and a feed speed of 2,000 feet per minute produces approximately 0.00119 inches of scallop depth, 0.278 inches of feed per knife, and 3.600 knife marks per inch.
• These are theoretical results assuming evenly spaced knives cutting equally. Actual surface finish also depends on knife condition, knife projection, machine vibration and wood characteristics. Reset restores the default inputs, and Print produces a summary of the inputs and results.

The calculator provides three results:

• Scallop depth: The calculated depth of the curved surface between successive knife cuts, expressed in inches or millimetres. A smaller value indicates a shallower theoretical cutting pattern.

• Feed per knife: The distance the material advances between successive knife cuts, expressed in inches or millimetres.

• Knife marks: The calculated number of knife marks per inch or millimetre of material.