United States
Department of
Agriculture
Forest Service
Forest
Products
Laboratory
Research
Paper
FPL-RP-480
Producing Studs
from Paper Birch
by Saw-Dry-Rip
Robert W. Erickson
Harlan D. Petersen
Timothy D. Larson
and
Robert Maeglin
Abstract
Paper birch, the second most abundant hardwood species
in the Great Lakes region, is greatly underutilized. The
major obstacle to the commercial use of paper birch is
warp. In this study, we compared the effect of two
methods of sawing (conventional and Saw-Dry-Rip (SDR))
and two methods of drying (conventional and high
temperature) on warp of paper birch studs. Effects of air
and dehumidification drying were evaluated only for SDR
sawing and for comparison of mean values with the other
four treatments. The SDR process significantly reduced
warp, particularly in 2 by 4 studs compared to 2 by 2 and
2 by 3 studs. The effect of SDR on warp was independent
of drying temperature; crook values obtained with
conventional temperature and dehumidification drying
were equal to those obtained with high temperature
drying. In general, there was a statistically significant
increase in warp, especially crook, during a l-month
storage period at laboratory conditions. However,
dimensionally stable studs were obtained from SDR
flitches kiln-dried at high temperature and maximum
venting to a uniform 5 to 6 percent moisture content. SDR
was most effective in reducing warp of studs from upper
logs. Problems encountered included dark wood (which
resulted in honeycomb and collapse) and excessive
thickness shrinkage. Darkwood can be minimized by
sorting logs, before processing, to eliminate darkwood.
Excess thickness shrinkage can be counteracted by
increasing target thickness from 1-3/4 inches to 1-7/8
inches. Our results indicate that the SDR process could
be used to minimize the amount of crook in both
structural and nonstructural lumber sawn from paper
birch, resulting in increased recovery and greater
utilization of this hardwood resource.
Keywords: Paper birch, Saw-Dry-Rip, SDR, Warp
November 1986
Erickson, Robert W.; Petersen, Harlan D.; Larson, Timothy D.;
Maeglin, Robert. Producing studs from paper birch by Saw-Dry-Rip. Res.
Pap. FPL-RP-480. Madison, WI: U.S. Department of Agriculture, Forest
Service, Forest Products Laboratory; 1986. 8 p.
A limited number of free copies of this publication are available to the
public from the Forest Products Laboratory, One Gifford Pinchot Drive,
Madison, WI 53705-2398. Laboratory publications are sent to over 1,000
libraries in the United States.
The Laboratory is maintained in cooperation with the University of
Wisconsin.
Producing Studs
from Paper Birch
1
by Saw-Dry-Rip
Robert W. Erickson
Harlan D. Petersen
Timothy D. Larson
College of Forestry, University of Minnesota,
St. Paul, MN
Robert Maeglin,
Supervisory Research Forest Products Technologist
Forest Products Laboratory, Madison, WI
Introduction
Demand on softwood species to meet structural lumber
needs in North America is increasing. However, supplies
of softwood timber have not increased to meet this
demand. In fact, many areas of the softwood forest in
northern Minnesota have become inaccessible for
commercial use because of the Boundary Waters Canoe
Wilderness Act (PL95-495). This shortage could be
partially alleviated by greater use of underutilized species,
such as paper birch (Betula papyrifera), which is the
second most abundant hardwood species in Minnesota
and other parts of the Great Lakes region and Canada
(Martodam 1983). In addition, the commercial use of
paper birch could obviate the ever-increasing cost of
transporting lumber from the southern and western
lumber-producing regions to midwestern markets.
Paper birch is a medium-density hardwood species with
an average specific gravity of 0.48 based on green
volume, which is about the same specific gravity as that
of southern yellow pine (Forest Products Laboratory
1974). The major obstacle to its commercial use is warp,
particularly crook. When studs are produced by
conventional methods, growth stresses cause crook to
occur at the headrig. Furthermore, additional crook can
develop in drying because of non- uniform longitudinal
shrinkage and the inherent low resistance of studs to
shrinkage forces. The Saw-Dry-Rip (SDR) process can
greatly reduce or eliminate crook that results from growth
stresses in the log. SDR originated at the USDA Forest
Service, Forest Products Laboratory (FPL) for the purpose
of increasing the utilization of low- to medium-density
‘This paper was supported in part by Mclntire-Stennis funds and is
entered as Paper No. 14019 in the scientific journal series of the
Agricultural Experiment Station, University of Minnesota, St. Paul.
hardwood species for structural lumber. It employs the
live sawing of logs into nominal P-inch-thick flitches,
drying the flitches, and then ripping them into studs.
Maeglin and Boone (1983) have described in detail the
principles behind SDR and its successful application to
yellow-poplar.
The primary objective of the research reported here was
to compare the amount of warp of conventionally sawn
paper birch studs with that of studs produced by the SDR
method. This research was phase 2 of a three-part study:
Phase 1, investigation of the drying of nominal 2-inch
paper birch flitches by various methods; phase 2,
comparison of the amount of warp obtained in
conventionally produced and SDR-produced studs; and
phase 3, comparison of the strength of studs dried at high
temperature and conventional kiln temperature. Results of
phase 1 have been published as an FPL research paper
(Larson et al. 1986), and phase 3 research is currently
underway.
Materials and Methods
The study was designed to evaluate the effect of SDR on
the reduction of warp in studs.
Design
The principal study design was a 2 by 2 factorial with two
replications. The secondary study design was a 2 by 2 by
3 factorial for within-group factors. The principal
treatments were two sawing methods (SDR live-flitch
sawing and conventional stud sawing) and two drying
methods (conventional and high-temperature). Half of the
flitches were ripped to green stud target dimension (for
conventional sawing), and the other half were dried as
wide flitches and then ripped to dried stud target
dimension (for SDR treatment). ‘The within-group variables
measured were the effect of storage, the position of studs
in the tree (butt logs and upper logs), and stud size.
Air and dehumidification drying were evaluated in addition
to conventional and high-temperature drying, but only in
conjunction with SDR and not with conventional sawing.
Mean values of warp for air and dehumidification drying
were compared with warp means for the four principal
treatments, using the Bonferroni test (Miller 1966).
Harvesting and Allocation of Logs
Paper birch trees 8 to 12 inches in diameter at breast
height (dbh) were harvested from the Superior National
Forest near Grand Marais, MN, and bucked into logs
100 inches long, using an average of four to five logs
per tree. Trees with excessive lean, rot, or extremely poor
form, and logs with more than 3 inches of sweep per
8 feet of length were excluded. Each log was marked with
its tree and log number and then end coated. Logs for the
study had a minimum small-end diameter inside the bark
(dib) of 4.5 inches.
Two hundred and sixteen logs were used for the study.
After the small end dib was measured, the logs were
sorted into l-inch-diameter classes (4.5-5.4 through
9.5-10.4 in). Commencing with the 5-inch class, the logs
were randomly allocated to six treatment groups; each
treatment had two replications. Butt logs were allocated
separately to insure an equal distribution to treatments
because studs produced from such logs of other species
have exhibited more crook than logs from upper tree
positions (Maeglin and Boone 1983).
Machining
The logs were live sawn into nominal 2-inch flitches that
were double end trimmed to 97 inches and then rough
edged. Flitches were numbered, block piled, wrapped in
plastic, and transported to the University of Minnesota for
cold-room storage (@33 °F) to await further processing.
2
Flitches were ripped by a nearby hardwood lumber
processor on contract. Green and dried flitches were
premarked for ripping into 2 by 2, 2 by 3, and 2 by 4
studs. We attempted to achieve maximum piece yield but
gave priority to the production of 2 by 4 studs.
Rough dry studs, both SDR and conventionally sawn,
were surfaced to a thickness of 1-7/16 inch and standard
finished widths of 1-1/2, 2-1/2, and 3-1/2 inches. The
less-than-standard thickness was the result of high
thickness shrinkage combined with sawing variation.
Drying
The treatments are described in table 1. In the
abbreviations used to define the treatments, the first and
second letters of each abbreviation designate the type of
sawing and drying, respectively; e.g., SH refers to SDR
processing and high-temperature drying. Treatment 1 is
subdivided into 1A and 1B because the wet-bulb water
supply was lost in drying the first kiln charge.
Consequently, the kiln vents were wide open rather than
closed overnight, and the intended wet-bulb temperature
of 190 °F was not maintained. A lower and more uniform
final moisture content (MC) resulted for treatment 1A
compared to 1B and to the other high-temperature runs
(Erickson et al. 1984).
We had previously discovered in phase 1 of this study
(Larson et al. 1986) that the “darkwood” of paper birch is
impermeable and subject to severe drying degrade.
Darkwood refers to tissue that is darker in color than
normal heartwood. It occurs in irregular patterns near the
heart of the tree, has higher MC than normal heartwood
and sapwood, and appears to have its origin associated
with branch stubs and possibly other tree wounds.
Darkwood may be bacterially infected “wetwood” (Ward
and Pong 1980). Some of it will develop honeycomb even
at air-drying conditions. It seemed apparent that an
extended equalization period would be required to reach
the desired goal of a final MC range of about 8 to
12 percent. Of course, only the steam-heated kiln afforded
the equalization option.
Each kiln charge contained six sample boards. Four of the
six boards contained varying amounts of darkwood,
whereas the other two were totally “whitewood.”
(Whitewood refers to all wood other than darkwood, and
consequently a given whitewood flitch could have been all
sapwood or a combination of sapwood and normal
heartwood.) There were eight samples for air drying, four
in each of two units.
Table l--Treatment description and drying conditions
Treatment
Treatment
description
Equalizing
conditionsa,b
Drying conditions
SHwbu
SDR/high temp drying/wet bulb
uncontrolled.
DB temp of 240 °F. Kiln vents wide
open for 14 h followed by 24 h at
WB temp of 190 °F.
DB temp of 200 °F and WB temp of
180 °F for 27 h.
SHwbc
DB temp of 240 °F and WB temp of
190 °F for 26 h.
DB temp of 200 °F and WB temp of
180 °F for 141 h.
SC
SDR/high temp drying/wet bulb
controlled.
SDR/conventional temp drying.
SD
SDR/dehumidification drying.
DB temp of 180 °F and WB temp of
160 °F. Approximately 24 h for each
of the two runs.
None.
SA
SDR/air drying.
Dried by FPL schedule T8C3. Average
drying time of 397 h for each of the
two runs.
1 HP unit. Average drying time of
460 h for each of the two runs.
Northern Minnesota air-drying yard
from May through November.
Stickered units were then covered
with plastic and stored outdoors at
Kaufert Laboratory during
December and January.
CH
Conventional sawing/high temp
drying.
DB temp of 240 °F and WB temp of
190 °F for 24 h.
DB temp of 200 °F and WB temp of
180 °F. About 44 h for each of the
two runs.
cc
Conventional sawing/conventional
temp drying.
Dried by FPL schedule T8C3. Average
drying time of 380 h.
DB temp of 180 °F and WB temp of
160 °F for about 90 h for each run.
None.
a
With the exception of treatment SHwbu, equalizing began when the driest sample board reached 7 to 8 percent MC and continued until the
wettest reached a MC of about 12 percent. In treatment SHwbu, the equalizing commenced when the wettest kiln sample was about
10 percent and continued until the average of all six sample boards was approximately 6 percent. There was a top load restraint of 60
lb/ft2 for all treatments except SA.
b
Total kiln residence was equal to the hours given under “Drying Conditions” plus the hours given under “Equalizing Conditions;”
DB = dry bulb, WB = wet bulb, temp = temperature.
Measurement of Moisture Content
of Dried Flitches and Studs
A resistance moisture meter was used to take readings
on about one-third of the flitches and conventionally sawn
studs soon after drying and again after machining and
storage. Readings were taken about 18 inches from each
end and at midlength. When a band of darkwood was
present, two readings were taken at each location: one
within the darkwood and another in the whitewood
adjacent to the darkwood. The insulated needles were
driven to a depth of 3/8 inch. After MC measurement the
lumber was stickered 4 feet on center, using 3/4-inchthick stickers, and stored indoors. After the lumber had
been stored for approximately 1 month, warp was
remeasured on all studs. MC was redetermined on the
same studs that were tested prior to storage.
Collection of Warp Data
Crook, bow, and twist were measured to the nearest
1/32 inch with a calibrated metal wedge. The initial
measurement was completed within 2 or 3 days after
planing, the second after storage.
For crook measurement, the stud was placed on a
perfectly flat table with the concave narrow edge down.
The wedge was inserted to refusal at the point of greatest
crook, which was normally at midlength, and the crook
was read to the nearest 1/32 inch. Bow was measured
similarly, with the wide face of the stud down. For the 2
by 2’s, bow was measured perpendicular to a 1-1/2-inch
face and crook perpendicular to a 1-7/16-inch face. For
twist, three of the four corners of the stud were made to
contact the table top, and the wedge was inserted under
the raised corner.
3
Results and Discussion
The effect of SDR can best be seen in a comparison of
the results of SC and CC treatments. The two treatments,
which used conventional-temperature drying, resulted in
similar final average MC (9.9 and 9.6 pct, respectively).
The total drying times were also similar, with 397 hours
for SC and 380 hours for CC (table 1). Yet, the average
crook of SC studs both before and after storage was
about one-half that of CC studs (table 2). Because final
MC, drying schedule, and drying time of SC and CC were
equal, the crook reduction for SC was apparently directly
and totally attributable to the SDR process,
The results showed that SDR improved stud quality in
paper birch. However, some adjustment may be
necessary in drying schedules and thickness of flitches.
Warp Data
With the exception of SA, all SDR treatments resulted in
considerably lower crook and less twist than treatments
using conventional sawing (table 2). The values for
average bow were approximately the same for SDR and
conventionally sawn studs. The poor performance of SAtreated studs is believed to have been caused by the high
MC of the flitches before ripping; the average MC was
16.1 percent, with a range of 11 to 23 percent.
Both SC and SD, which were dried at comparatively low
kiln temperatures, had crook values essentially equal to
those for the more successful high-temperature SDR
treatment, SHwbu. This suggests that SDR can significantly
reduce crook in the production of 2 by 4’s from paper
birch independent of kiln-drying temperature.
Consequently, the SA treatment may have produced warp
results equivalent to those from SHwbu if drying had
produced comparably low and uniform levels of MC in the
flitches.
Crook increased in all studs during storage, but the
increase was least for the kiln-dried SDR treated studs.
Of the SDR treatments, crook-increased most in SAtreated studs. Again, this is believed to have been caused
by high MC at the time of ripping and subsequent drying
of the machined studs during storage. Average bow for
initial and after storage measurements followed the same
pattern as crook for all six treatments. With the exception
of SH-treated studs in which twist decreased, there was
generally a slight increase in average twist during storage.
Figure 1 compares the percent of 2 by 4’s rejected
because of crook, by treatment and time of measurement.
Rejection is based on warp limits for STUD grade lumber
set by the National Grading Rule for softwood structural
lumber (Northern Hardwood and Pine Manufacturers
Association 1978, U.S. Department of Commerce 1970).
The best treatment was SHwbu, with no rejects at the initial
measurement and 4 percent rejects after storage. About
20 percent of the conventionally sawn studs were rejected
at the initial measurement and about 22 percent after
storage. With the exception of SA, the rejection rates for
SDR-treated studs were far lower than for conventionally
processed studs.
CC, CH, SC, and SD studs were similar in their initial
average MC (9.6, 9.3, 9.9, and 8.9 pct, respectively). After
storage, however, crook of CC and CH studs was double
that of SC and SD studs. This illustrates that drying in the
flitch form restrains and/or removes longitudinal growth
stresses. The conventionally sawn studs, which warped at
sawing, did not receive the balanced stress reduction of
SDR. Consequently, the warp remained to interact with
longitudinal shrinkage while the pieces further dried during
storage.
Table 2–Warp and moisture content of paper birch 2 by 4 studs after initial drying and after storage of 30 or more days
Treatment
SC
SHwbu
SHwbc
CC
CH
SDc
SA c
Number
of
2 by 4’s
72
Average crook
(1/32 inch)
Initial Remeasure
Average twist
(1/32 inch)
Average bow
(1/32 inch)
Initial Remeasure
Average
moisture content
(percent)
Range of
moisture content
(percent)
Initial Remeasure
Initial Remeasure
Initial Remeasure
2.7
3.0
4.2
4.0
5.1
6.9
5.5
7.4
2.1
3.2
2.6
1.9
(
)b
(
)b
7-17
< 7-7
3.6
5.1
5.8
5.7
1.0
0.8
(
)b
(
)b
< 7-8
4.9
5.5
3.1
4.9
7.6
7.2
4.0
6.8
5.9
4.7
5.5
5.9
4.7
6.0
5.4
5.2
4.7
3.6
1.6
2.6
5.4
3.8
2.4
3.7
24
39
50
61
57
66
a
Moisture content values determined using a resistance moisture meter.
b
Meter readings were below the minimum dial reading of 7 percent.
c
Sawing methods were not compared for these drying trials; all studs were processed by SDR.
4
9.9
8.3
9.6
9.3
8.9
16.1
8.1
8.1
7.3
8.0
8-11
7-13
7-11.5
11-23
7-10.5
( )b
< 7-7.5
7-10
7-13
7-8
7-10
Statistical Analysis
Results of the Bonferroni test (Miller 1966) for differences
in the means showed that the kiln-dried SDR-treated
studs had significantly less crook than conventionally
sawn or SDR air-dried material (a = 0.05) both initially
and after storage.
Additional statistical comparisons were restricted to the
studs dried by conventional and high temperatures. These
were the only drying methods which were used in
conjunction with both sawing methods.
Figure l-Percent of 2 by 4’s rejected because of
crook, by treatment and time of measurement.
(ML86 5216)
The percent of rejects for all studs (2 by 4, 2 by 3, 2 by
2), by treatment and time of measurement, once again
shows the superiority of the kiln-dried SDR studs to the
conventionally sawn studs (table 3). All three forms of
warp, i.e. crook, bow, and twist, were represented in the
percent of rejects. For further clarity, table 4 shows the
number of studs rejected by warp type. At the initial
measurement, a total of 72 studs were rejected for the
6 treatments; 2 studs were rejected because of bow, 4
because of twist, and the remainder because of crook.
After storage, the total number rejected was 115: 4
because of bow, 13 because of twist, and the remainder
because of crook. It is apparent that crook was the major
form of warp and that the kiln-dried SDR treatments were
quite effective in reducing crook. This is especially true for
the SHwbu treatment, which dried the material to a uniform
5 to 6 percent MC. As a consequence, only one SHwbu­
treated stud was rejected after storage because of warp,
and that for twist. The other drying methods could
probably produce equally good results if drying times
were sufficiently extended to produce comparable
uniformity of MC. This certainly suggests that the current
practice of drying studs to a maximum MC of 19 percent
is grossly inadequate because of the potential for drying
and warp during storage.
The failure to make STUD grade because of warping can
mean significant dollar losses. These data show the ability
of SDR to greatly increase the recovery of STUD grade
material. The warp reduction demonstrated for paper
birch may be important not only for the production of
studs but also for non-structural use such as furniture,
paneling, etc.
In the analysis of variance, the effect of sawing type on
crook was highly significant; there was no significant
effect on bow or twist (table 5). This was expected, for
SDR is designed to minimize crook, whereas bow and
twist are affected by uniform sawing, proper stacking, and
stress balance in flitches (Maeglin and Boone 1983).
Drying method did not have a significant effect on the
three forms of warp or on the sawing/drying interaction.
The effect of stud size was significant for all three forms
of warp (a = 0.05) (table 6). This is attributable to the
greater amount of crook and bow in 2 by 2’s and the
larger values of twist in 2 by 4’s. A significant interaction
of size with sawing method existed only for crook
(a = 0.05), probably due to greater crook in 2 by 2’s.
Increases in warp during storage were significant at the
5 percent level for all three types of warp. Crook and
twist are most subject to increase during storage with
additional drying. As discussed earlier, the increase in
crook during storage of conventionally sawn 2 by 4’s was
about twice that of SDR-processed studs.
A significant interaction was observed between crook and
tree position of logs after storage. The average increase
in crook for studs from butt logs was 0.9/32 inch. For the
studs from upper logs the increase was 0.4/32 inch.
Therefore, the difference in the increase in crook for studs
sawn from butt and upper logs can probably be attributed
to the interaction of log position and storage.
Table 3 summarizes the rejects by treatment and log
position. All stud sizes were combined for the purpose of
these comparisons. The percentage of rejected
conventionally sawn studs was approximately four times
higher than that of kiln-dried SDR-treated studs. Of further
interest is the origin of the rejected studs. Thirty-two
percent (13 of 41) of the rejected conventionally sawn
studs came from butt logs; 75 percent (9 of 12) of the
rejected kiln-dried SDR studs came from butt logs. These
data illustrate the ability of SDR to almost totally eliminate
rejection caused by warp of studs produced from the
upper logs. The greater tendency for warp to occur in
studs from butt logs agrees with data reported by Maeglin
and Boone (1983).
5
Table 3–Rejection rates of treated studs according to log position in the treea
Treatment
Number
of studs,
all sizesb
Number of
rejects,
all sizesb
Percent
rejects,
all sizesb
SH c
SC
CH
cc
SD
SA
136
150
130
117
121
128
5
7
22
19
3
16
3.7
4.7
16.9
16.2
57
4
7.0
61
5
8.2
59
9
15.2
45
4
8.9
54
2.5
5.6
3
12.5
9
17.0
53
MEASUREMENT AFTER STORAGE
79
89
71
72
SHc
SC
CH
CC
136
150
130
117
121
128
11
13
29
25
8.1
8.7
22.3
21.4
57
61
59
45
10
27
8.3
21.1
54
53
79
89
71
72
67
75
Number
of studs,
butt logs
Number
of
rejects,
butt logs
Percent
rejects,
butt logs
Number
of
upper logs
Number of
Percent
rejects,
rejects,
upper logs upper logs
INITIAL MEASUREMENT
SD
SA
9
10
14
7
9
11
67
75
15.8
16.4
23.7
15.6
16.7
20.8
1
2
13
15
0
7
1.3
2.2
18.3
20.8
0.0
9.3
2
3
15
18
2.5
3.4
21.1
25.0
1
16
1.5
21.3
a
Based on STUD grade warp requirements (Northern Hardwood and Pine Manufacturers Association 1978).
b
Includes 2 by 2, 2 by 3, and 2 by 4 studs.
c
Combined data for SHwbu and SHwbc.
Table 4–Number of studs rejected, by warp type, before and after storagea
Treatment
Number
of studs
Crook
Initial
Remeasure
Bow
b
Initial
Remeasure
Twist
Initial
a
All sizes (2 by 2, 2 by 3, 2 by 4) combined.
b
Measurements were retaken after 30 or more days of storage.
c
Sawing methods were not compared for these drying trials. All studs were processed by SDR.
6
Remeasure
Total (all warp)
Initial
Remeasure
Problems Due to Darkwood
Darkwood for all kiln-dried treatments had a higher MC
than the whitewood. The range in final average MC for
many of the treatments was quite large, which illustrates
the difficulty of removing moisture from darkwood and the
effect of darkwood moisture on total drying time and final
uniformity of MC.
Honeycomb occurred in all treatments. It was most severe
in conventional and high-temperature drying, least severe
in air drying, and essentially restricted to the darkwood.
Darkwood also tended to collapse and surface check,
commencing in the early stages of drying. Selection of
logs to reduce the presence of darkwood is
recommended. It may even be beneficial to dry flitches
with darkwood separately under a different schedule.
Thickness Shrinkage of Flitches
The flitches for this study were sawed to 1-3/4-inch
thickness. Shrinkage was too great to dress the dried
lumber to 1-1/2-inch thickness, so the final product was
dressed to 1-7/16 inch to achieve fully dressed studs.
Thickness target size should therefore be increased to
1-7/8 inch to compensate for shrinkage.
Table 5–Analysis of variance for crook, bow, and twist in
relationship to sawing and drying method
Source
Mean
square
df
F
CROOK
Sawing (S)
Drying (D)
SXD
Error
1
1
1
4
Sawing
Drying
SXD
Error
1
1
1
4
Sawing
Drying
SXD
Error
1
1
1
4
280.61101
.52068
.24100
4.62132
a
60.72097
.11267
.05215
BOW
.03450
1.52510
6.99840
27.98451
.01233
.05450
.25008
26.62934
2.68002
4.21682
5.69397
4.68027
.47068
.74058
TWIST
a
Significant at the 1 percent level.
Table 6–Analysis of variance for crook, bow, and twist. The
relationship of stud size on sawing and drying
Source
df
Stud Size (Sz)
Sz X Sawing (S)
Sz X Drying (D)
Sz X D X S
2
2
2
2
Stud
Sz X
Sz X
Sz X
Size
S
D
DXS
2
2
2
2
Stud Size
Sz x S
Sz X D
Sz X D X S
2
2
2
2
Mean
square
F
CROOK
95.13058
62.83587
2.66499
.04577
a
21.19184
13.99768
.59367
.01020
a
BOW
20.59908
1.23719
5.64441
2.73649
a
5.30047
.31835
1.45239
.70414
TWIST
45.21596
5.48844
.20967
1.53033
a
23.22662
2.81725
.10770
.78610
a
Significant at the 5 percent level.
7
Literature Cited
1. The SDR process significantly reduced crook in kilndried studs. Neither SDR nor conventional sawing
significantly affected bow and twist. SDR was most
effective in reducing warp of studs from upper logs; only
1.3 percent of studs from upper logs were rejected after
treatment.
2. SDR air-dried studs were not significantly different in
warp from conventionally sawn studs regardless of drying
temperature. This was apparently due to insufficient
drying. We expect that SDR would have reduced the warp
of air-dried flitches if a lower MC had been achieved. SDR
is most effective in reducing warp when the final MC is
low and uniform.
3. The effect of SDR on warp was independent of kilndrying temperature. Crook values for SDR with either
conventional-temperature or dehumidification drying were
essentially equal to those obtained for SDR with high
temperature drying.
4. After approximately 1 month of stickered storage, the
percent of rejected studs from all but one of the
treatments increased significantly, mostly because of
increased crook. (Most of the increased warp was
attributed to postdrying of darkwood.) SDR treatments
had the fewest rejects. Dimensionally stable studs were
obtained from SDR flitches kiln-dried at high temperature
and maximum venting to a uniform 5 to 6 percent MC.
5. Darkwood caused degrade because of warp and
honeycomb. Therefore, selection of logs with clear,
whitewood ends is recommended in order to reduce the
amount of darkwood.
6. High-temperature drying of paper birch flitches caused
thickness shrinkage as high as 12 percent. This should be
taken into consideration when setting green target sizes
for paper birch. Perhaps 1-7/8-inch thickness rather than
1-3/4-inch thickness should be used.
8
Erickson, Robert W.; Petersen, Harlan D.;
Larson, Timothy D. Obtaining uniform final moisture
content in the high temperature drying of paper birch
flitches. Forest Products Journal. 34(2): 27-32; 1984.
Forest Products Laboratory. Wood handbook: Wood as
an engineering material. Agric. Handb. 72, revised.
Washington, DC: U.S. Department of Agriculture, Forest
Service: 1974.
Larson, Timothy D.; Erickson, Robert W.;
Boone, R. Sidney. Comparison of drying methods for
paper birch SDR flitches and studs. Res. Pap. FPL 465.
Madison, WI: U.S. Department of Agriculture, Forest
Service, Forest Products Laboratory; 1986. 13 p.
Maeglin, Robert R.; Boone, R. Sidney. Manufacture of
quality yellow-poplar studs using the saw-dry-rip
(S-D-R) concept. Forest Products Journal. 33(3): 11-18;
1983.
Martodam, Dave. Evaluation of Minnesota white birch for
potential use in a system 6 manufacturing processwhite birch resource analysis. Minnesota Department of
Natural Resources; 1983.
Miller, R. G. Simultaneous statistical inference. New York:
McGraw Hill Book Co. 1966. 272 p.
Northern Hardwood and Pine Manufacturers Association.
Standard grading rules. Chicago, IL: Northern
Hardwood and Pine Manufacturers Association 1978;
125 p.
Rasmussen, Edmund F. Dry kiln operator’s manual. Agric.
Handb. 188. Washington, DC: U.S. Department of
Agriculture; 1961. 197 p.
U.S. Department of Commerce. American softwood
lumber standard PS 20-70. Washington, DC: U.S.
Government Printing Office; 1970. 26 p.
Ward, James; Pong, W. V. Wetwood in trees: A timber
resource problem. Gen. Tech. Rep. PNW-112. Portland,
OR: U.S. Department of Agriculture, Forest Service,
Pacific Northwest Forest and Range Experiment
Station. 1980. 56 p.