29
3.3.3 Data Analysis
In this study, we analyzed the correlation between dependent variable equilibrium contact angle and independent variables frequency of lathe check
and Ra values by using multiple linear regressions. The model was as follow Y = α + β
1
X
1
+ β
2
X
2
where, Y
= equilibrium contact angle value α
= constant β
1
, β
2
= regressions coefficient X
1
= frequency of lathe check X
2
= Ra values Analysis of varianceANOVA of multiple linear regression were calculated
by minitab16 in order to obtain the effect of frequency of lathe check and surface roughness to equilibrium contact angle at 95 confidence level p0.05.
3.4 Results and Discussion
3.4.1 Variation of veneer thickness
Uniformity of veneer thickness is a very important factor affecting the quality of glue bond strength in LVL or plywood. The results presented in Figure
14a-c show that a slight thickness variations of rotary cut sengon, jabon and
poplar cultivars veneers are observed.
Figure 14 Variation of veneer thickness from pith to bark of sengon a, jabon b and poplar cultivars c
2.5 3
3.5
2 4
6 8
T hick
ness o
f ven
ee r
m m
Segmented rings from pith to bark Unboiled sengon
Boiled sengon a
2.5 3
3.5
1 2
3 4
5 6
7 8
T hick
ness o
f ven
ee r
m m
Segmented rings from pith to bark Unboiled jabon
Boiled jabon b
2.5 3
3.5
5 10
15 20
25 30
T hick
ness o
f ven
ee r
m m
Segmented rings from pith to bark Lambro
Soligo Taro
c
30 The thickness of jabon veneer peeled from some bolts, which was intended
to be 3.0 mm, varied from the lowest 2.50 mm to the highest 3.38 mm. The veneer thickness of sengon varied from the lowest 2.50 mm to the highest 3.80
mm. Since our spindle less rotary lathe was not able to peel 3 mm veneer, so that the targeted 3 mm veneer thickness was not accomplished. However, the
uniformity of veneer thickness variation from pith to bark was reached with coefficient variation less than 6. Coefficient of variations of the veneer thickness
from pith to bark calculated was 1.02 for the jabon veneers from unboiled log and 2.17 for the jabon veneers from boiled veneers. The coefficients of
variation of veneer thickness from pith to bark of unboiled and boiled sengon were 3.65 and 3.05, respectively.
Different from sengon, the variation of veneer thickness of poplar cutivars were less varied. Poplar logs resulted satisfactory veneer thickness without
boiling treatment. The veneer thickness ranged from the lowest 2.62 mm to the highest 3.07 mm. Coefficient of variations of the veneer thickness from pith to
bark calculated were 2.20 ‘lambro’, 2.06 ‘soligo’ and 1.74 ‘taro’. By considering all the coefficient of variations was less than 6, the bolts of sengon,
jabon and poplar cultivars were correctly peeled to maintain the thickness regularity.
3.4.2 Lathe check frequency, depth and length
The average values of lathe check frequency per cm of veneer length taken from the loose side of the veneer of sengon, jabon and poplar cultivars were
presented in Figure 15a-c.
Figure 15 The progress of lathe check frequency from pith to bark of sengon a, jabon b and poplar cultivars c veneers
2 4
6 8
10 12
10 20
30 Nu
m ber
o f
lath e
ch ec
k
per cm
v en
ee r
len gth
Segmented rings from pith to bark Lambro
Soligo Taro
1 2
3 4
5 6
7
1 2
3 4
5 6
7 8
Nu m
ber o
f lath
e ch
ec k
per cm
v en
ee r
len gth
Segmented rings from pith to bark Unboiled jabon
Boiled jabon
1 2
3 4
5 6
7
1 2
3 4
5 6
7 8
Nu m
ber o
f lath
e ch
ec k
per cm
v en
ee r
len gth
Segmented rings from pith to bark Unboiled sengon
Boiled sengon a
b
c
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