Conventional wood planers generate objectionably high noise levels which can be readily associated with reverberant vibration approximately the production of the resistive part of the radiation impedance and the square of the space-time averaged transverse vibrational velocity which forms the acoustic power radiation. The radiation resistance constitutes one of the components of the acoustic efficiency of the source, the radiating area, and the properties of the reverberant workpiece. The resulting sound generation from a vibrating workpiece increases with increased workpiece width and generally increases in the magnitude of approximately six decibels upon doubling of workpiece width. This characteristic results from the sound spectra by frequency components approaching the critical frequency of the workpiece. Although it has been conventional to employ helical cutterheads for wood planers with continuous cutting blades and a low helix angle, as well as a number of knife blades, minimal attention has been directed to the generation of the high noise level until governmental standards have imposed certain restrictions. Although many types of conventional wood planar cutterheads employ replaceable cutter segments, and achieve high efficiency in cutting rates, these conventional cutterheads are extremely noisy and the noise level increases substantially with the width of the material being planed. Reduction of wood planer noise levels from workpiece vibration is not only desirable but mandatory at this time, and reduction in radiation resistance and workpiece vibrational velocity are highly desirable to achieve reduced levels of noise during cutting in cutterhead design utilizing a continuous cutting blade, high helix angle, and a relationship between the factors of helix angle, cutterhead diameter and the number of knife blades which are in continuous contact with the workpiece.
Accordingly, it is an objective of this invention to provide a helical cutterhead for wood planers which will reduce noise level by reducing radiation resistance and vibrational velocity by having more than one knife blade engage the workpiece at any instant.
Another objective of this invention is the provision of a helical cutterhead for wood planers which will effectively reduce the noise level during the cutting or planing action by providing a helical cutterhead in which the helix angle is designed by taking into consideration a continuous cutting edge, high helix angle, a relationship between helix angle, cutterhead diameter, and the number of knife blades that will insure continuous contact between the cutterhead and the workpiece whereby more than one knife blade will engage the workpiece at any instant by satisfying the minimum formula condition of L=.pi.D cot.phi./N in which L is the contact distance, D is the cutterhead diameter, N is the number of knife blades, and .phi. is the helix angle of the knife whether a continuous blade or a series of segments constituting the cutting blade along the helical blade angle, and the resulting L is less than 4 inches.
Other objectives and many of the attendant advantages of this invention will become more readily known to those skilled in the woodworking technology from the accompanying drawing and a detailed description of one preferred embodiment of this invention.