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
31 The average frequency of lathe check tended to decrease from pith to bark of
the veneers. The veneers near the pits showed larger frequency of lathe check. The average value of frequency of lathe check per cm veneer length of unboiled
and boiled sengon were 2.5 and 1.8, respectively Figure 15a. Frequency lathe check of jabon per cm veneer length were 4.1 unboiled and 3.5 boiled Figure
15b. The average values of frequency of lathe check per cm veneer length of poplar cultivars from juvenile and mature wood were 5.3 and 4.3, respectively
Figure 15c. Lathe check frequency of juvenile veneers was higher than that of mature veneers. The average frequency lathe check per cm veneer length were
5.0 ‘lambro’, 4.6 ‘soligo’ and 5.3 ‘taro’. Several researchers also observed the same trend on 2 mm jabon veneers Kabe et al. 2013 and sengon veneers
Darmawan et al. 2015. Higher lignin content of the wood near the pith could be responsible for high frequency of lathe check of the veneers taken from the inner
parts of the sengon, jabon and poplar cultivars logs. Bao et al. 2001 noted that juvenile wood is an important wood quality attribute because it can have lower
density, larger fibril angle, and high more than 10 lignin content and slightly lower cellulose content than mature wood. Higher frequency of lathe check near
the pith could be also caused by smaller radius of its natural curvature in the bolt, which imposed greater tension during the flattening.
The results in Figure 15a-b also reveal that veneers with lower average frequency of lathe checks are produced by boiled sengon and jabon bolts for 4h at
temperature of 75
°
C, compared to unboiled bolts. This result gave an indication that boiling at 75°C resulted in better surface properties of the veneers. It could
be announced that sengon and jabon bolts boiled for 4h at 75
o
C could be proposed before manufacturing veneers. The boiling of sengon and jabon bolts at the
temperatures and periods is considered to soften their bolts during the peeling process. A softening process does temporarily alter the microstructure of the
wood, making it more plastic due to thermal expansion of cellulose, and softening of lignin in the cell wall Jorgensen 1968. The softening by heat has produced a
degree of plasticity roughly 10 times than that of wood at normal temperature Peck 1957. Therefore the flattening of the veneer from its natural curvature is
more easily accommodated with less formation of lathe check.
The frequencies of lathe check per cm veneer length near pith were 5.9 and 5.0 for unboiled and boiled jabon, respectively. The lathe check frequencies near
bark were 2.0 for unboiled jabon and 2.1 for boiled jabon. According to Darmawan et al. 2015, the thicker the veneer peeled from the logs tend to
produce larger frequency of lathe check compere to thinner veneer. Kabe et al. 2013 found that the frequencies of lathe check for 2 mm jabon veneers are 2.6
for unboiled and 1.4 for boiled. The frequencies of lathe check per cm veneer length near pith were 3.9 and 2.9 for unboiled and boiled sengon, respectively.
The lathe check frequency near bark were 1.5 unboiled sengon and 0.7 boiled sengon. The results presented by Darmawan et al. 2015, the frequency of lathe
check for 2 mm sengon veneers are 2.03 for unboiled logs. Sengon veneers checked less than jabon veneers Figure 15a-b. This results was correspond to
Forbes 1997 who stated that fine pores wood tend to check less than larger pores wood. The average pores diameter of sengon is 170 µm, while jabon is 175 µm
Martawijaya et al. 2005 see Figure 1a-b
