Research into the cutting characteristics of bandsaws has shown that the average cutting path of the sawblade is biased to one side of the ideal cut path. It has also been shown that a strong correlation exists between this cutting bias and sawblade deviation. This report is the second on the topic of bandsaw cutting bias and describes the development and mill trials of a PC based, self aligning bandsaw guide system. This system uses data from the sawblade, and programmable logic controllers controlling the bandmill, to monitor bandsaw cutting behaviour and align the guides to minimize the cutting bias and sawblade deviation. The system is shown to effectively reduce sawblade deviation and unscheduled blade changes and compensate for damaged or poorly prepared blades.
The effect of bandsaw roll-tensioning and bandmill axial forces on the stresses in the blade, on the interaction of the blade with the bandmill and on the stiffness and cutting accuracy of the sawblade are examined. The stresses due to roll-tensioning are measured and their effect on frequency and stiffness determined. The effect of the blade-wheel geometry on the stresses in the cutting region are analyzed showing how the stresses, frequency and stiffness of the sawblade relate to its cutting accuracy. Empirical relationships are developed that enable the stresses due to roll-tensioning to be estimated. Analytical methods accurately predict the effect of roll-tensioning on blade torsional frequency and lateral stiffness. A model was developed that successfully predicts the effect of overhang on the stress in cutting region of the blade. Both analytical and experimental results confirm that rolling in the centre 60% of the sawblade will increase blade stiffness while rolling outside this region will reduce it. Cutting accuracy is shown to be strongly related to lateral tooth stiffness, and it is also shown that optimum increases in stiffness and improved cutting accuracy are obtained by confining the roll-tensioning to be close to the blade centre-line.
Across North America the amount of tensioning used in bandsaws varies drastically. Sawblades tensioned to fit circle gauges from 28 feet to 80 feet in diameter are in regular use and performing very well. This raises the questions as to what is the right amount of tension and what effect does it have on cutting accuracy. In this study, the cutting accuracy of five sawblades, with varying levels of tension, have been measured and compared. The results show that little change occurs in cutting accuracy once enough tension has been put into the blade for it to fit an 80-ft circle gauge.
This paper investigates the feasibility of increasing bandmill production by proportionally increasing both blade speed and lumber feed speed. A modal analysis of the bandmill and bandsaw was conducted and resonant conditions, likely to impair performance, were identified. Cutting tests were conducted to determine the effect of increased blade speed on cutting accuracy, surface finish and sawdust quality. The tests were conducted at blade speeds of 10,000 fpm, 12,500 fpm and 15,000 fpm and examined the effect of tipped and swaged blades cutting Coastal Hem/Fir and Interior SPF.
The global objective of the project is to investigate the feasibility of increasing bandmill production by proportionately increasing both the blade speed and the lumber feed speed. The objective of this phase of the project is to transfer the results of the laboratory experiments to the sawmill industry. The work described in this report covers the transfer of the technology to two sawmills. The first report has a more detailed introduction to the project and a review of the literature.
A significant percentage of rough-cut unseasoned cedar products are down-graded due to excessive roughness caused by fiber pulling. An exploratory study was carried out to reduce or eliminate this problem. It was found that inclining the feed direction in relation to the saw movement significantly reduces degrees of fiber pulling, indicating that the problem of down-grading due to fiber pulling may be at least partly solved. Boards that show no or insignificant fiber pulling did not change their surface roughness due to the fact that the roughness on the boards is solely the function of bite per tooth. Nevertheless, this type of board always makes the grade and therefore is not a problem. Further studies are needed to accurately determine the benefits of inclined feeding or sawing directions.
The primary objective of the study is to measure the effect on cutting accuracy of side grinding swaged tooth bandsaws. The effect of side grinding on surface finish is included for comparison with previous work.
Swaged tooth bandsaws tend to leave quite a rough sawn surface. Cutting with large bites or uneven teeth aggravates this problem. Previous studies have shown that side grinding could improve surface finish but it was not shown to have any effect on cutting accuracy. However, sawmills and saw manufacturers have indicated that side grinding can improve cutting accuracy. Therefore, this contradiction needs to be resolved in order to quantify any benefits from side grinding.
The results indicate significant improvements in cutting accuracy and surface finish are possible. Side grinding 17-gauge and 16-gauge bandsaws respectively improved sawing accuracy up to 22% and 44%, reduced sawblade lateral displacement up to 36% and 68% and improved the sawn surface finish up to 24% and 11%.
Extremely careful bandsaw fitting and tooth alignment was necessary in the preparation of side ground saws. This cost-time-effectiveness has to be considered when adding side grinding to swaged saw preparation.
Research into the cutting characteristics of bandsaws has shown that, in nearly every case studied, the average cutting path of the saw is biased to one side of the ideal cut path. This paper presents the results of a laboratory investigation into this off-centre cutting. The influences on the shape and cutting behaviour of bandsaws of such basic factors as bandmill strain, guides, guide alignment, and blade overhang, are measured. It is concluded that bandsaw blades are curved in the cutting region and angled slightly out of the cut. The curvature and angle of the blade are due to the interaction of the bandsaw with the bandmill wheels, in the presence of bandmill strain, overhang and wheel crown, and are relatively insensitive to bandmill strain or pressure guides. The curvature and angle of the blade in the cutting region are most likely the cause of the cutting bias.