With the pressures on our industry at this time, sawmills are using thinner saws to try and improve recovery without reducing current production levels. This has led to washboarding becoming a widespread problem in the industry. Washboarding is a wavy pattern that appears on the surface of lumber due to excessive vibration of the sawblade as it cuts through the lumber. In this study the washboarding behaviour of saws was studied at both the analytical and experimental levels to develop a much better understanding of the problem and lead to a set of guidelines for industry use.
This was a joint project between Forintek Canada Corp. and The University of British Columbia. Dr. S. G. Hutton led the analytical side of the work and Dr. J. Taylor the experimental portion of the work. This report is a portion of the overall research endeavour and presents the results of the experimental work that was conducted.
To compliment and validate the analytical portion of the work a series of cutting tests were conducted to examine the washboarding phenomenon and the factors that influence its occurrence. The effects of wheel rotation speed, strain, tooth bite, and depth of cut were examined and their effects recorded. As small changes in tooth design are known to influence a saws washboarding behaviour, but are not accurately predicted by the mathematical models, we also carried out cutting tests with saws of different thickness and tooth pitch, progressively increasing the length of the tooth face and the depth of the gullet until washboarding on the lumber surface was quite severe. In this manner we hoped to be able to develop some guidelines for the industry.
It was apparent from the initial tests that there were two types of washboarding. We have called the larger diagonal waves that often appear with industrial sized bandsaws, Type I. The narrow more vertical pattern or that on circular saws is called Type II. The results in this report are primarily associated with Type I and show the somewhat insensitive nature of the washboarding instability to changes in the operating parameters. The occurrence of washboarding is more sensitive to changes in the tooth geometry.
Manufacturing analysis using computer flow simulation has been applied successfully in pilot projects to several Alberta value-added wood products companies in the sectors of re-manufacturing and furniture manufacturing. This project continues these pilot projects examining the application and potential benefit in manufactured/prefab homes. An Alberta manufactured/prefab home manufacturer was selected for this project. The wall-line was chosen for this study. The study was accomplished through detailed observations and data collection, which identified several bottlenecks that included the framing table, squaring table and the linear configuration of the line. From observations, the squaring table was labour intensive and the material handling equipment was quite slow. At the framing table, the stud grade being used contained many twisted and bowed boards, which required additional time to align and fasten the studs. Lastly, the single-line configuration created bottlenecks during the transition from sheathed and unsheathed products. From observations and discussions with staff, potential improvement scenarios were developed. Simulation models were developed for each of these scenarios to evaluate their effectiveness and return on investment. The scenarios examined were: affect of panel sheathing ratio, improving efficiency at the squaring table, improving efficiency at the framing table, addition of a branch-line for unsheathed products and the addition of the branch-line in combination with increased efficiency at the framing table. The implementation of pre-cut OSB panels was simulated to reduce processing times at the squaring table by 30%, which increases throughput by 15%. The addition of a branch-line for unsheathed products showed a potential production increase of 10.8%. However, the simulation models also showed that the framing table could not maintain a consistent supply to the squaring table. The use of a higher stud grade was modelled showing a potential production improvement of 17.5%. As a result, the potential benefits in this particular wood products business demonstrates that computer flow simulations can be applied to Manufactured/Prefab Home manufacturers and may potentially have further implications in other similar Alberta value-added industries.
A report on the results of tests on the feasibility of using ceramics for saw blade tips. The major factors determining whether it is practical to use ceramics are the physical attachment of the tip to the blade, the inherent brittleness of the material and its wear characteristics.
In the laboratory testing two distinct washboarding patterns were obtained. They are labeled as Type I and Type II (Figure 1). For bandsaws, Type I washboarding is the one with he washboarding pattern at about 45 degrees. Type II washboarding is usually associated with small bites and the pattern slopes at 20 to 30 degrees from the path of the saw teeth. Although we obtained some data on the Type II washboarding, this report is associated only with Type I, as this is the type most often encountered in the primary sawmilling industry and is of principal concern to Forintek's members. It should be noted that the same two types of washboard exist for circular saws; however, these are not covered here.
The effect of the many variables listed above on the range of washboarding in bandsaws has been experimentally examined in some detail. The results are presented in this report along with some guidelines for the elimination of washboarding. Although much valuable data have been obtained during this study, more research is required in order to obtain a complete understanding of washboarding. The recommendations given in this document were found to be effective for 16, 17 and 18 ga. blades on a 5 ft. bandmill, but can be expected to be helpful for other sizes of bandmills also.
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.
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.
When large saws are operated at high speeds cutting accuracy deteriorates and very high levels of oscillation occur after the blade exits the cut. These high oscillation levels may adversely affect the next cut. This report describes laboratory tests that were conducted to determine if the addition of extra guides would improve the response of such blades.
Tests were carried out with four different guide configurations: a front guide; a front guide plus a pin guide; a front guide plus a pin guide plus a back guide; and a front guide plus a back guide. The results indicate that the addition of the extra guides has a marked effect upon blade response. In particular, the addition of a back guide results in a significant change in wedging of the cut boards.
The results presented indicate that extra guides could be useful in reducing cutting deviation. Further work is required to determine the appropriate location of such guides and whether the addition of such guides can be accommodated in a mill situation.
This report covers three days of testing on the primary breakdown line at the Pope and Talbot sawmill in Spearfish, South Dakota. Significant increases in production were achieved by using variable speed drives on the feed system and quadruple bandmills. By selecting rim speeds that provide the better cutting accuracies, this increase can be obtained with little or no increase in sawing deviation. In addition variable pitch sawblades alleviated washboard problems at all rim speeds tested and showed a small improvement in cutting accuracy. There appeared to be some alignment problems with the quad that were temporarily overcome by shimming the guides.