Fundamental Aspects of the Wood Cutting Process

To economize research efforts, it would be useful to discover fundamental approaches to all wood machining processes. In wood cutting, a single cutter of variable shape takes a variable path through a work-piece at a variable speed, and at a variable angle to the grain. Wood itself presents important variables of mechanical properties with species and moisture content. The cutting process can be regarded as a sequence of separate actions defined by Reinke in 1950–chip severance, break-up, and removal. Since research work with normal cutting speeds is difficult and expensive, it is important to know whether results observed at conveniently low speeds can also apply to high speeds. A review of work done on the effect of cutting speed on cutting forces shows disagreement. It appears that in these studies of high-speed cutting several other influences are at work: there is an increase in cutting forces at higher speeds due to increased straining rate, which is opposed by decreases in forces due to higher temperatures and reduced friction. The shape of the cutting force curve should thus depend on the variation of these three interacting factors. However, these experiments have dealt with a percussive action affected by dynamic properties of the system of wood, tool, machine, and measuring device. To reduce the effects of impact, continuous cutting on a lathe was chosen as a process to investigate. An increase of cutting speed from 0.5 inch per minute to 28,000 feet per minute caused a small increase in cutting forces which was predictable on the basis of chip inertia, with no distinguishable change in surface quality. Observations were made of the effect on the cutting process of several variables?species properties, moisture content, cutting angle–and two failure types were distinguished–splits along the grain below the cutting plane, and splits in a plane perpendicular to the grain and parallel to the cutting plane, at a variable distance below it. This work defined what was required of an analytical model on which to base failure predictions. A model for cutting with both cutting edge and velocity vector at 90? to the grain (rip-sawing), based on the theory of a beam on an elastic foundation, proved valuable. Equations were derived to predict failure types in relation to surface quality and cutting efficiency. The model proposed still has limitations, and a more exact analysis for the problem of indentation of a cellular material by a rigid wedge is needed.

You must be logged in to download any documents. Please login (login accounts are free) or learn how to Become a Member