Studies on the Characteristics of Wood Cutting Force of the Whole Saw-chain Used in a Chain-saw Machine (2)

Comparison of Recent four Commercial Types of Saw-chain Tooth

Abstract

With the aid of the test stand mentioned in Part 1 and using four commercial types of saw chain, i. e. chipper type (51CP-75E), semi chisel type (72DP-81E) and chisel typer (72LP-81E & 76LP-81E), the characteristics of wood cutting force of the whole saw chains were investigated. The material tested here is spruce produced in North America with rectangular cross section of 20cm×20cm and moisture content of about 14 percent. As already mentioned in Part 1, the measured forces to cut timber were independent of the frictional resistance between the saw chain and bar rail and the reaction of the discharged saw dust in this experiment. The results obtained are as follows:
1) To carry out the cutting experiments, the velocity of the saw chain V_H was set in the range of 2.2-17.6m/s and feed speed V_V 1.7-16.1mm/s. The velocity and the feed speed were examined in various combination to obtain a wide range of velocity ratio λ. As a result, it was clarified as shown in Fig. 6-9 that the relation between the velocity ratio λ and the tangential cutting resistance force F_H and the normal cutting resistance force F_V could be expressed by following empirical formula.
F_H, F_V=c/(λ+a)+b
where a, b and c are the constant obtained from the experiment
By this formula, of the velocity ratio λ can be kept constant for timber cutting, the tangential cutting resistance force F_H and the normal cutting resistance force F_V can be determined.
2) The ratio of the normal cutting resistance force to the tangential cutting resistance force, i. e. force ratio F_V/F_H, was proved to be independent of the velocity ratio λ and remained constant except for 76 LP type saw chain. It was also clear that F_V was one half of F_H and angle of the resultant force was about 26 degree as shown in Fig. 10, This angle indicates the direction of the resultant cutting force and the amount of this can be regarded as an index of the cutter tooth biting into the timber. From this viewpoint, the biting ability of 76LP type saw chain at high speed and light load, i. e. when the velocity ratio λ is in a larger region, becomes somewhat dull compared with the other three types.
3) To compare the ease of cutting for the tested four types of saw chains, a specific cutting resistance force per one cutter tooth f_H was examined. As an undeformed chip thickness δ becomes a function of the velocity λ, the relation between δ and f_H was investigated as shown in Fig. 11. As a result, 72LP type saw chain was found to be the sharpest followed by 76 LP, 72DP and 51CP in that order.
4) Based on the facts described above, net cutting horsepower vs. engine speed and feed rate was calculated from the standpoint of effective usage for a one man gasoline engine chain saw. Furthermore, taking a few factors into consideration, a method to obtain brake cutting horsepower requi red to drive a saw chain was suggested.