Influence of edging practiceson cutting yields of Alaska bich lumber

David L NichoII*J.w. Funck*

C.C. Brunner*J.E. Reeb*

AbstractBirch lumber is often characterized by a high degree of knots, barkpockets, heartwood, and other features which force

sawmill owners-to decide whether to edge and trim boards to produce standard grade lumber vs. proprietary grade character- marked lumper . ln addition,the edging strategies used with irregularly shaped flitches can greatly influence cut-stock recovery. To investigate this recovery; 143 kiln dried 4/4 birch flitches were-obtained from a sawmill in south-central Alaska and eval-uated by a National Hardwood Lumber Association (NHLA) grader, forboard grade and lumbertally. Each flitch was, markedby the lumber grader; indicating where the board would.be edged to produce NHLA grade lumber in a production.setting, Theflitches were transported from Alaska to Oregon State University where they were scanned to produce digital board data. Thesedata were then processed with the computer simulation program CORY (Computerized Optimization of Recoverable Yield) toestimate the cut-stock yield for various levels of edging severity and sound feature (character mark) inclusion.

Four edging strategies were evaluated, ranging from unedged (least severe ) to-wane-free (most severe). As expected, cuttingarea recoveries and cutting yields were reduced as edging severity was increased. In many cases, however, these differenceswere minimal. Cutting yields for clear parts were 21.1, 23.7, 26.2, and 27.1 percent for wane-free, actual, light, and unedgedstrategies-respectively. Cutting yields for parts that included sound character features increased by more than double to 44.0,49,0, 52.7,.and 54.0 percent for wane-free, actual, light, and unedged strategies, respectively; These results indicate that findingvalue-added alternatives for this character-marked birch might prove profitable for some Alaskan sawmills that also producesecondary products such as cabinets and furniture or supply cuttings to these manufacturers.

The birch(Betula papyrifera Marsh) resource in Alaskais prevalent, including close to 100 million cubic feet ofyoung sawtimber growing stock on about 140,000 acres insouth-central Alaska (Campbell et, al., 2005). Despite thissubstantial resource, birch lumber production in Alaska islimited to just a few sawmills. There is generally strong in-terest in birch products among lumber producers and retailstore managers in Alaska (Nicholls 2002). But, there aremajor obstacles to its widespread use including obtainingdependable log supplies, achieving consistent moisture con-tent (MC) in kiln-dried lumber, and matching appearanceand character features to desired end products.

Lumber sawn from birch often has relatively large propor-tions of heartwood, which is considered a defect under theNational Hardwood Lumber Association (NHLA) gradingrules (NHLA 2003). Consequently, its boards provide toofew clear (i.e. defect free) cuttings of adequate size to pro-duce higher grade lumber. Further, decay is common in

FOREST PRODUCTS JOURNAL • VOL. 59, No. 1/2

Alaska birch. One study which involved dissecting 600 birchtrees grown in Alaska found that only 10 percent lacked decayand virtually all included at least some natural stain (Trummer2001). While the more valuable grades of lumber require largeproportions of clearwood, the increasing popularity of rusticstyle products may favor inclusion of character features such

The, authors are, respectively, Research Forest Products Tech-nologist. USDA Forest Serv. Pacific Northwest Research Sta.,Sitka, Alaska (dlniclolls@fs.fed.us); Manager, Lumberand WoodSci, Weyerhaeuser Company, Federal Way Washington, and for-merly Associate Professor, Dept. of Wood Sci. and Engineering,Oregon State Univ. Corvallis, Oregon (jim.funck@weyerhaeuser.com); and Associate Professors, Dept of Wood Sci. and Engineering,Oregon State Univ., Corvallis, Oregon (charles.brunner@oregonstate.edu, jim.reeb@oregonstate.edu). This paper was received for publi-cation in January 2008. Article No.10452.Forest Products Society Member.©Forest Products Society 2009.

Forest Prod. J. 59(1/2):29-34.

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as heartwood, small-sound knots and bark pockets, and stain.Among these products are birch kitchen cabinets, which werefound to have strong consumer acceptance when character fea-

.:tures such as knots and bark pockets were included (Donovanand Nicholls 2003).

Edging practices greatly influence lumber grade and prof-itabilitv because under standard NHLA rules, wane allowanceis as much a factor-in determininggrade as other features suchas knots, holes, stain, mineral streak, decay, splits, and checks(NHLA 2003). The Alaskan sawmills processing birch find itdifficult to produce the higher lumber grades in quantities suf-ficient to justify investing in optimizing edgers, machinesdesigned to maximize allowable wane and, consequently,value. Therefore, they must rely on trained operators to man-ually edge their. boards, which .is a practice that has beenshown to produce less thanmaximum value much of thetime(Flann and Lamb 1966, Bousquet 1989, Kline et al.1991,Regalado et al.1992, Schmoldt et. a1. 2001).

A larger marketsuch as trading proprietary lumber gradesdeveloped specifically to satisfy the needs of secondary man-ufacturers producing rustic style products, might justify theproduction of more birch lumber-and automated processing.Such a proprietary market exists for red alder lumber in thePacific Northwest but it takes the cooperation of both pro-ducers and sellers to be developed. Along with determiningthe type and size of sound features to include ina proprietarygrade of the issue of wane allowance is also important becauseedging practices have been shown to greatly affect cutting-stock yields(Beaudoin et. al; 1982, Brunner et al;1996). Wengertand Lamb (1990) estimated that-each additional sixteenth ofan inch reduction in edging resulted in an increase in yield of1.5 percent.

In practice, optimum edging is a complex decision-makingprocess that requires trained mill personnel to quickly eval-uate board grade, value, surface measure, and trimmingallowances. Schmoldt et al. (2001) estimated that humanoperators make optimal decisions only 62 to 78 percent ofthe time, while Regalado et a1. (1992) found that edgingand trimming operations at three hardwood mills producedonly 65 percent of the lumber value possible with optimal edg-ing practices. Kline et al. (1991) found that the greatest loss invalue occurred when non-optimal edging reduced potentialFirst and Second (FAS) boards to No.1 Common grade. Theyalso found that lumber volume increased at two hardwoodsawmills by 17 and 23 percent with optimum edging and trim-ming, respectively,

One common finding of edging optimization research hasbeen that even relatively minor changes in edging practicescan influence both volume and value recovery of lumber.Brunner et al. (1996) found that the change (vs. normal millpractice) in cut-stock volumes of red alder lumber rangedfrom.a 7-percent.decrease to a 13-percent increase depend-ing on the degree of edging. In that study, more high-value,longer cuttings were produced at the higher recovery levels.Kline et al. (1993) found that furniture parts produced fromunedged and untrimmed material resulted in volume gains ofup to 25 percent vs. actual edging as practiced by mills. Otherstudies have shown a potential for increasing hardwood lum-ber value by more than 20 percent through optimum edgingand trimming (Bousquet 1989). The financial impact ofproper edging can be substantial. In a vertically integratedhardwood mill producing 20 million board feet (MMBF)

of lumber per year, annual income could be increased anestimated $2 million through optimum edging practices(Brunner et al. 1996). .

Clement et a1. (2005) investigated alternative edging prac-tices for processing short logs as a means of increasing theutilization of the white birch (Betula papyrifera Marsh.) re-source in Quebec; Canada. While they did not investigateedging practices or overall lumber recovery, they concludedthat higher furniture part yields were obtained with conven-tional vs. short-log processing. But, differences were mini-mized by selecting appropriate cutting bills for eachprocessing alternative.

Given-the findings of past research and the challenges ofeconomically processing birch lumber in Alaska, the researchreported in this paper is an attempt to consider ways of im-proving utilization of this resource, The objective was to de-termine what degree of edging severity (based on fourscenarios), when applied to a sample of Alaska birch lumber,would result in the greatest lumber yield under NHLA gradingrules. A secondary objective was to consider the influence oncutting areas and cutting yields of allowing specific sounddefects.

Materials and methodsSample material

In this study, 143 kiln-dried, unedged birch flitches wereobtained from a sawmill in south-central Alaska. The Alaskabirch trees harvested to produce these-flitches were locatedapproximately 60 miles north of Anchorage, Alaska, and treesaveraged about 60 to 80 years of age. All of the flitches werenominally 8 feet long. Flitches were graded by an NHLAgrader into four NHLA grades, with the greatest proportionbeing No. 3A Common. The grader also marked each flitchwith edging lines indicating the board's width when edgedto obtain maximum grade. These widths ranged from 400inches to more than 9.0 inches, with a relatively uniform dis-tribution. Table 1 providcs details on volume and width dis-tribution by grade. The flitches were then transported fromWasilla, Alaska, to the Department of Wood Science andEngineering at Oregon State University, Corvallis, Oregon,where they were imaged for further study.

Board data collectionA computer-controlled imaging system, consisting of

a Hitachi HY-C20 CCD color camera mounted on a lineartrack and connected to a Truevision TARGA + image captureboard was used to create coordinated image data forboth sidesof the boards. The imaging system's spatial resolution was 15

pixels per inch across the flitch width and 11.25 pixels per inchalong the flitch length. Software developed at Oregon StateUniversity was used to extract feature data from the boardssuch as board shape and defect size, type, and location.

The data set was then used as input to a simulation programto estimate cut-stock yields for various edging practice and

cut-stock quality combinations.

Cut.stock simulationA three-stage, rip-first, fixed-width, random-length version

of the CORY (Computerized Optimization of RecoverableYield) board cut-up program (Brunner et.al. 1989, Anderson

et. al. 1992) was used to determine the volume of cut-stockparts that could be produced from the imaged flitches. Thecutting bill included fixed widths of 1.5, 2.0, 2.5, and 3.0inches, while the random lengths ranged from a minimumof 6 inches to a maximum of 38 inches. Lengths longer than38 inches were sawn into two parts to reach an acceptable size.

Four different edging strategies were evaluated usingCORY simulations. The unedged strategy retained the entireflitch as imaged. Light edging produced edges that were atleast one-third of a flitch's length, which given the nominallength of the flitches created the potential to have a contiguous

. clear edge matching the maximum clear cutting length 38inches. The actual edging strategy used the area inside theNHLA grader's marks: the wane-free strategy removed allwane,

The.birch lumber from this part of Alaska contains signif-icant amounts of sound natural features, such as heartwood,tight knots, sound rot, and sound insect damage. With the mar-·ket for rustic-style material increasing, several scenariosthat take advantage of this material's natural character were

created to estimate the added yield from producing rustic cut-stock instead of the typical clear cut-stock. The clear cuttingscenario consisted of normal clear, two-face parts with bothfaces completely free of defects. Three rustic grade scenarioswere designed to produce cut-stock with increasing amountsof sound defects. The first scenario accepted tight knots, thesecond accepted heartwood, and tbe third accepted tight knots,heartwood, and sound incipient decay and insect damage.

The edging strategies and cut-stock scenarios resulted in 16simulated production runs, one for each possible combina-tion. Results were-compiled for each grade, and theindividualand average cutting yields were calculated.

Results and discussionAverage cut-stock yields

Figure 1 shows the percent area yields averaged across allof the grades for the 16 combinations of'.simulated edgingstrategies and cut-stock qualities, Table 2 lists these sameyields for each edging strategy. The yield is not identical tothat used in industry because the calculations in Table 2 arebased on the edged board's bounding box area (the-board'smaximum width times its maximum length) and nota grader's estimated surface measure. The yields for thewane-free and actual edging strategies probably approximatethose based on a grader's calculations, but the light and un-edged would not. While not a true measure of availableboard area, the bounding box provides a relative measureof the board area that must be processed and is a very goodindicator of th board volume occupying a dry kiln, Becausethe base area becomes smaller as edging severity increases,percent yields increase as more non-usable wane is removed.This can be viewed as improvingboard conversion effi-ciency but at the same time wane is removed so is usablewood, resulting in a loss of cut-stock. Figure 2 shows howedging strategy and cut-stock quality affect the amount ofcut-stock that can be produced from the same board resource.Both views give useful insight into rough mill processing andproduction but from very differeiit perspectives.

Relative cut-stock productionand edging strategies

Perhaps a more understandableapproach is to compare cut-stockproduction against a constant base.The most obvious choice is touse the 'grader's edging marks, oractnal edging strategy, because itmore closely represents typical in-dustry practice. Figure 3 showshow much of each edging strategy'smarginal board area is convertedto cut-stock. Marginal area is cal-culated by subtracting the actualedging strategy's bounding areafrom an alternative edging strat-egy's bounding area. Then, thisnumber is divided into the gainor loss in cut-stock from the ac-tual edging's cut-stock productionand converted into a conversion ef-ficiency percentage. Table 2 liststhe conversion efficiency for every

31FOREST PRODUCTS JOURNAL VOL. 59, NO.1 12

combination iof edging strategy and cut-stock quality.It also shows the percent gain or loss in cut-stockcompared to the amount produced by the actual edgingstrategy.

Relative cut-stock production and cut-stock qualityFigures 1 through 3 and Table 2 show that cut-stock

quality had an even greater effect on production than theedging strategies. Adding allowable features obviouslytranslated into more usable wood to be converted into cut-stock. With the actual edging strategy, accepting tight, redknots resulted in only a small increase in recovery, which is

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not surprising given that they oc-cupy only 1 or 2 percent of boardarea. Accepting heartwood intoa rustic cut-stock resulted in almosta doubling in production, and ac-cepting all sound features producedmore than twice the amount of cut-stock as the clear category. Theeffect of the unedged strategy oncut-stock production had similarpatterns, regardless of the qualityof the cut-stock, but the light andwane-free edging strategies exag-gerated results even more as addi-tional sound features were allowed.When all of the sound defects werealJowed, light edging resulted inalmost half of a square foot ofcut-stock for every added squarefoot of bounding area, whilewane-free edging lost two-thirdsof a square foot. These results arenot surprising given that heartwoodaccounted for 3 to 30 percent ofboard area depending on lumbergrade. Therefore, once it was al-

lowed, most wood left or removed from a board was likelyto become cut-stock.

Relative cut-stock production and board gradeThe pattern of changing cut-stock production with board

grade and edging strategy is fairly consistent across the fourcut-stock categories. The change in production for No. 1Common increased more with unedged strategy than the othergrades, while No.2 Common increased the least. The No.3Common grades were usually somewhere between No. 1 andNo.2. This is most likely due to the distribution of widths bygrade as well as the specific grading rules regarding wane.

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Cut-stock production and board widthBoard width played a role in cutting yield, but it was not

consistent (Figs. 4 and 5). This was especially true for thecase where only clear, two-face parts were allowed and maybe due to the fact that the fixed-width version of the CORYprogram was used, This created the potential for various boardwidths to have a greater opportunity for allowing differentcombinations of fixed widths to fit. When all of the soundfeatures were allowed, however, the trend was clearer thatwider boards produced higher cutting yields for each edgingstrategy. Edging strategy also had an effect for each boardwidth, but the benefit was reduced as board width increased.

ConclusionsProducing cut-stock parts from birch lumber from south-

central Alaska represents a viable option for creating high-value wood products from clear cuttings. Due to the high pro-portion of features found in birch however, edging strategiesthat optimize the tradeoffs between defect features and lum-ber value should be considered. Key considerations forAlaska wood products firms often include how much charac-ter and what types of features to include in birch lumber fordifferent products. This study found that heartwood and wanewere, by a wide margin, the two most important features af-fecting the recovery of cut-stock parts from this sample of

birch lumber. Cut-stock yields were

FOREST PRODUCTS JOURNAL VOL. 59, NO. 1/2. 33

substantially higher when sounddefects such as heartwood, soundrot, tight knots, and sound insectdamage were allowed,

This study also found that edgingpractices, ranging from unedged towane-free strategy, had a great in-fluence on this material's cuttingyields, It appears that a light edgingstrategy could substantially increasecut-stock production over actual orwane-free edging strategies. But,the secondary wood products in-dustry in Alaska has raw materialrequirements and processing equip-ment that may differ Significantlyfrom that of larger hardwood saw-mills, Most hardwood producers inAlaska do not currently sell lumberbased on NHLA grading rules butrather rely on customer preferences(without any formal grading system),

Further, most producers edge lumber based on criteria otherthan maximizing volume. For example, a common practiceis to remove all wane for use in products such as paneling,flooring, and mouldings. This practice should be reconsideredwhen producing cut-stock parts where some wane may beadvantageous in terms of yield. The development of newgrading rules for Alaska birch lumber could actually benefit

cut-stock production and value, particularly if rustic gradeswere established. This scenario would be similar to the highlysuccessful path followed by red alder lumber markets in thePacific Northwest Sawmill expansion to the scale needed forcut-stock part production in Alaska could allow sawmills toproduce a variety of cuttings for products such as furniture,panels, and flooring.

AcknowledgmentsThe authors would like to express their appreciation to Pop-

pelt Milling, Inc., Wasilla, Alaska, for its valuable assistance.This project was partially funded by USDA Grant AwardNumber: PNW 04-JV-11261975-175.

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