CURVE SAWING. Larry Guenther Plum Creek Timber Company Colville, WA

Transcription

1 CURE SAWING Larry Guenther Plum Creek Timber Company Colville, WA Curve sawing is not a new technology. There are, and have been numerous systems developed to saw on the contour or sweep of the log. Sawing on the curve dates back to the early 900's when it was developed to make chair and wheel parts. There have been a number of patents issued for curve sawing. Generally these were based on the premise of a curve linebar, roll system, or a combination of rolls and linebars. The system Plum Creek's Arden operation is using was developed by U.S.N.R. and uses both rolls and a linebar on a linear positioner. The U.S.N.R. System has a scanner, a canter and two gang saws, an 8" and a 2" double arbor. This does two things, it scans the log to recover the most wood fiber and determines the best continuous arc for that log. The system cants, or opens the log on a continuous (tangent) arc to minimize bending the saw while in the cut. The scanner also determines which gang to route the cant to and positions the positioning pins at the infeed of the gangs. Why go to Curve Sawing? What are the advantages and disadvantages? With the available log supply decreasing and the logs that are available becoming smaller, it is necessary to manufacture the log so as to recover all available fiber. Being able to saw logs on the curve allows recovering more of the log into longer useable lengths. It also allows for sawing more closely to the grain of the log which reduces warpage when drying plus the moisture content is more consistent the full length of the board. Without curve sawing, the log needed to be bucked in shorter pieces to reduce the sweep, or the log had to be squared up by sawing off the "horns" on one side and the "belly" on the other side to be able to get a piece of lumber with enough length. Once the log was squared up, the board now had heartwood on both ends if sawn from the "belly" side (Figure ). By following the contour or closely to the contour of the log, the moisture content is more consistent the length of the board. By sawing the same log as in Figure, on the curve or arc of the log, we not only get longer and more lumber, but we get lumber that is cut more consistently along the same moisture content of the log. There will still be some difference in moisture between the edge and middle of the piece (Figure 2). You will notice on Figure, when the log was straight sawn, the volume of lumber recovered was.3 board feet, but when the log was sawed on the curve (Figure 2) the volume of lumber increased to 6.5 board feet; a 2.6% (text continued on page 28) WDKA 23 May, 995

2 , Top Face, A = 8ot. Face, > = Left Side < = Ri ght5i de I = Sublet LenCel Is Plot Si ze = 3.9 by 8.9 (in). Width = I /. Length = / 2..7 a " Pi ece Nb: 6 ' ^ - - I / CUTrentTinne 7. II-APR ,6 5:59: A Yi vvl ti Time Of Soon 37. APR-/ :07: vv: Nb Description Length 63. /x 5.3 6' 2 /x6 8.0 I6' /x ' 75.6 /x6 6.0 I6' 6, /x6 '7.0 ' /, ' /0.33 CP ,6 33,9. rav AN AO AO ( in) 6 " r r t ro v Avv! = Top Face, A = Not. Face, > = Left Si de < = Ri ghtsi de I = Sublet LenCel Is Plot Size = 3,9 by 8.9 (in). Width = I /. Length = I / Y" " Pi ece Nb: 9 v e-, I. T;; k. A rw-rhy A :i, GUrrantTirre 7,- \ ilyi:;,c\. I -APR-995 6:0: , 't's \ k ( in) Deflection =.8 Ti rre Of Scan -APR-995 : Nb Descri pti on Length li. I /,3.0 6' 2 /,6 8.o 6' 3 /x ' AAll /x ' it% ': m IQ 5 X It 5/x ' IrAll, 6 /x6.0 ' t+ 7 / x3 3.5 ' fv! a : - It - i`f?,, - A I 6.:: (;/.:, ; ; Jv I ^f I - gr. fv t f,./t. cd F FIGURE. Log sawed conventionally..3 board feet FIGURE 2. Same log sawed on the curve. 6.5 board feet of of lumber were recovered. lumber were recovered, a 2.6% increase from Figure,

3 Top Face, ^ rr, Sot. Face, > Left Side < R'ghtSide I = SubSet lencells Plot Size = 3.9 by 8.9 (in). Width = /. Length = I / , I 2. iy I ^ 3 t ^ 5 L ao I- 6 IY : I; IN l Piece Nb: 25 0NrrentTirre 26-APR-I 995 5:0: APR-995 0:3:30.0 Nb Description Length /x3. 6' 2 /x 6' 3 /x3 3.5 ' /x3 a.r> 2' 5 /x3 2:3 0' 6 /x3.5 6' /9. ed. Ft- - Top Face, ^ Bat. Face, > Left Side <R'ghtSide I = SubSet LenCells Plot Size, 3.9 by 8.9 (in). IMdth = I /. Length I / , , , > 9 Piece Nb: 22 Current Ti me 26-APR-I 995 :5: APR-995 0:3:30.0 Nb Description Length /x3.o 6' /x b.9 6' /x 5.3 6' /x 5.9 6' /x.7 ' /x.3.9 0' ;:9 ed. Ft ( in) (I in) Deflection = 3.00 FIGURE 3. Smaller log sawed conventionally. 9.7 board FIGURE. Same log sawed on the curve board feet of board feet of lumber were recovered. lumber were recovered, a.6% increase from Figure 3.

4 ' = Top Face, 0 - But. Face, > = Left Side < = Right Si de - Sublet LenCells y our = Uut. race, > = Left Si de < = Ri gill St de = Sublet LenCel I s Plot Si te. 3.9 by 8,9 (In). Width = I / 3. Length = I / 25. Plot Si ze by 8.9 (in). N dth = I / 3. Le igth = I / Piece Nb: 5 2. Pi ece Nb: 9 ^ < ev en 6.9?"" - Wulf. )) :: -- iv " Cu. CurrtntTinvz 7. " J 30-APR APR '^ " : 3:53: I 5: 8: " I 29.9 q". $ al '. I 3-APR-I 995 I3-APR "I., : 27: :27: ,6 Ypi Nb Descri pti on Length Nb Description Lengt 6' I /x3 6' 63. n :: /23 6' 2 /x 6' 69. / 2 /x 75.6, t :s. 3 /x 6' 3 /x 6' 8.9-6' /x 6' 3 /x " A 5 /x3 2' 5 /x3 6' 89, - e '' 95. AA,7'.O Ød r,3.. a :":v i t 'lc i ^ 5. - i' yli','' 2. l ^ii 27.6 ; v; Y j<'.:. -? : 7. '-.. /f,, :: ; : ::,r: 59.9 :: ' i et "7, ' y -.Ai,7i ;, " J ',,', > < W ( in) FIGURE 5. Log with only 0,5" of curve, sawed conventionally. ( in) Deflection = 0.52 FIGURE 6. Same log sawed on the curve. There was only a.%i ncrease from Figure 5 due to the small amount of sweep.

5 = Sot. Face, > = Left Si de < - Ri ght Si de I = SubSet LenCel s Plot Si ze by 8.9 (in). NI dth = / 3. Length i= I / 2.. Pi ece Nb: 6 v y A "- tli. J* c9 i. 3 q - Io. r2` t y yin S.f 9.6, A N i :". A Y,, ) v >.. :.., , I 73. r> ' A r. ( in). Current Ti rre,,,. 30-APR-995 :A 8:0:30.80 A i ^ 'i 28-MAR-995. I A. '. 0 AI :28: ".. i Nb Descri pti on Length L /3 6' t, liv 2 /x6 6' ; 3 /6 6' /x6 6' '''''.: 5 /6 6' 6 /x6 6' ifsi 7 /6 6' 8 /x3 ' /. 7 I` f Figc FIGURE 7. Log with only 0.37" of curve, sawed conventionally. = Top Plot Si ze Face, A But. Face, > Left Si de < 3.9 by 8.9 (in). Width = / 3. = 2 * ghtsi de I = SubSet Length / 2. LenCel Is. Piece Nb: 5 A -.F Y^ <, "'ttpre7;*5tt7 ;. v 30-APR vi AA :36:53.2 ry " I AA 29.9 A., r., AR :20:7.77 I tl.9. 6 Nb Descri pti on Length "A / 6' : If /x6 6' I. u., I' 3 /x6 6' v:' 75.6 /x6 6' <; 8/.9 I '2 5 /x6 6' 89. ;' 6 7 I! vv;.) 6 /x6 "... 6' P y 95, - 7 /x6 6' ',/ 'A 8 Inn ' /x6 0' ''''. I II 8. II 5. - > Y 2. - IY v fl v = vy..,. u 7.,. v " i ;';',' 53.6 I. Y A. f. le 59.9 I U i :;7:; A.. i A A.. varil-, I I ) $ ate ft I f A, h I if v : ilvd < in) Deflection = 0.37 FIGURE 8. Same log sawed on the curve. There was only a.% increase from Figure 7 due to the small amount of sweep.

6 increase. This log had a curve or deflection of.8 inches over 6 feet. Figures 3 and show a smaller diameter log with a curve of 3 inches over 6 feet. The board footage on the straight sawn log was 9.7 versus 27.9 board feet when sawed on the curve. An increase of.6%. Keep in mind that not every log has this much sweep in it. Figures 5 and 6 are a " cant, 6.5" wide with a.5 curve and the increase is.%. Likewise, figures 7 and 8 are a 6" cant, 0" wide with.37 inches of curve and the increase is 5%. Of the logs we process, 5% have no sweep; 26% less than inch; 3% from inch to 2 inches and 7% over 2 inches (Figure 9). As far as disadvantages, there have been very few. The life of the saws are shortened some because of some bending. There can be problems with the boards loading on lugs downstream if there is much curve. This has been a very minor problem. Even though the log is sawn on the curve, the lumber has a tendency to lay flat. By the time the lumber is dried and surfaced, there is no indication that is was sawn on the curve. FIGURE 9. Percent of logs in mix (vertical axis) having sweep a given amount of sweep (horizontal axis). WDKA 28 May, 995