Principal Developments in Thin Circular Saw

Part 2: Reduction and Control of Saw Vibration

R.Szymani and C. l .Mote. Jr.

University of California, Forest Products Laboratory, Richmond, California

Vibration and Control Research

1. Saw design and process specification

1.1 Tapered, segmented and laminated Saws

The saw thickness tape, with radius can be beneficial for stability. Experiments by Mote and Holoyen showed that a major contribution of the saw taper is the control blade heat flux induced by the blade workpiece interaction. Friction between the blade and workpiece occurring near the hub introduces a thermal stress state favorable to blade stability similar to tension. Thermal tensioning of tapered blades during cutting has also been investigated by Berolzheimer and Best [1959] and Halleck [1968]. In the Scandanavian countries the process of inducing heat by friction is known as "'packing". Johnston [1960] studied the performance of a two-piece segmented circular saw. The lira section was riveted to a center that allowed displacement radially under thermal strains. A hard alloy tipped saw consisting of eight segments held between

two fiat discs has been discussed by Trusov and Trusova [1963]. According to these authors, segmental saws have been introduced in the Soviet Union for cutting particle and fiber boards. Johnston and St-Laurenl [1973] discussed segmented circular saws with removable cutters. Such a saw can be fitted with 2-16 evenly spaced cutters of rectangular cross section. The saw produces a good surface finish and high cutting accuracy, with the principal limitations of relatively small cutting height and large kerf. Compound or laminated saws were first discussed by Meins [1963] and Grinkov [I967]. The current laminated saw blades consist of two steel plates which are often separated by a dissipative layer. They dissipate energy by surface interaction and by doing work in this inner layer [Wikner 1975].

1.2 Slots

The usually intended purpose of slots or holes is to reduce compressive peripheral hoop stresses caused by temperature gradients. The slots allow saw expansion without development of stresses and the holes increase cooling. The geometric plate stiffness resulting from stresses m the plane of the saw increases, and the conventional or flexural stiffness of the saw decreases to a lesser extent if the slots are favorable to stiffness. As a result of these stiffness modifications, the frequency spectrum shifts tip in the important frequencies, and the critical instability speed of the saw increases. Experiences of Berolzheimer and Best [1959], Pahlitzsch and Rowinski [1967a], Mckenzie [1973] and Ratliff [1973] support tile introduction of uniformly spaced narrow radial slots or enlarged gullets [Kemov I968] for improvement of stability. On the other band, Barz [1965] and Stakhiev [1972] independently report the use of radial edge slots to be relatively ineffective, and they recommed the introduction of annular slots near the hub.

The number and length of slots have been determined by cut-and-try methods. So-calle Strob-saws are equipped with two slots extending from the rim to the saw blade clamping plate. In most cases saw blades have four or five radial slots having length up to 1|6, saw radius. Theoretical analysis of the effect of slots and holes have been conducted by Mote [1970b, 1972] and verified experimentally by Ellis [t976]. These analyses show that the slotted saw, which is geometrically unsymmetrical, does not form a standing wave at critical speed. The number of resonant frequencies of the saw is doubled because of a frequency splitting phenomenon associated with the sims, and resonance can occur at each frequency [Mote 1970a]. When the slotted saw is excited at resonance, the saw amplitude is less than that occurring in the symmetric saw (no slots) with the same excitation. The amplitude reduction occurs because the saw response energy is more distributed throughout the spectrum [Ellis 1976]. In summary, then, radial slots destroy the inherent symmetry of the circular saw and they modify the thermal stress state. Asymmetry prevents standing waves and the significance of tile thermal stress state modification depends upon the operating environment: it may be a positive effect and increase the instability speed or it may be negative. The slot questions have not been thoroughly treated and deserve further attention.