Veneer cutting and drying properties

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Veneer cutting and drying properties
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Forest Products Laboratory (U.S.)
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USDA, Forest Service, Forest Products Laboratory ( Madison, Wis )
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Full Text
(J II j PV CV
SOI'" I 110 1< ~I 's( I \ A '1O I il B 1 1 'I f I (
I '. D) PAI I M I OIF A(,I( III II ll
VENEER CUTTING ANI) D)RYIN(G I'PR(,')I' I I.S
TANOAK
Tanoak or tanbark oak (Lithocarpus densiflorus (Hook. & Arn. ) Rehd.
is the most abundant hardwood species found in the coast ranges of
California and southwest Oregon (1 2). 1 Thlie tree occurs from sea
level to 5, 000 feet (3). On favorable sites, forest-grown tanoak trees
have clear, straight boles for considerable heights. Mature trees
are 70 to 90 feet tall and 2 to 4 feet in diameter (11).
The wood is hard, heavy, and strong (1). The strength of tanoak is
nearly equal to that of the best true oaks (Quercus spp. ) (9). The
heartwood is light brown tinged with red, and its formation is believed
to be due to fungal infection. On the logs cut at the Forest Prodiucts
Laboratory, the heartwood zone was small and generally confined
to the portion of the log that normally is left in the core of rotary-cut
bolts (table 1). The sapwood, which may be several inches thick,
is light reddish-brown when freshly cut (1). The color darkens with
age.
The bark of tanoak is rich in tannin, and in past years the chief user
of the species has been the leather tanning industry. Its other
uses are for fuel, mine timbers, and occasionally furniture. The
sapwood has been found easy to treat with preservatives (11).
The wood works easily with tools, but because of its hardness and
heaviness it dulls tools more rapidly and requires a greater amount
of machining power than do lighter and softer hardwoods (2).
The lumber is difficult to dry and may surface check, end check k,
collapse, and warp. Kiln-drying schedules for tanoak have been
published by the Forest Products Laboratory (14).
1
-Underlined numbers in parentheses refer to literature cited at the
end of this report.
Report No. 1766-15 October 1959
i Maintained at Madison 5, Wisconsin in cooperation with thc University of Wisc ,, in




Description of Logs Tested

Rotary veneer cutting and slicing tests were made on three lots of
tanoak logs from Humboldt and Sonoma Counties, California. 2 Many
logs were eccentric in shape. The logs from the 1947 shipment
contained little bark when received at the Laboratory. These logs
had deep end checks, and all were badly surface checked. Table 1
provides a more complete description of all test logs.
Based on the test logs described in this report, the main defects to
be avoided in the selection of tanoak veneer logs are knots, shake,
end and surface checks, tension wood (10), and pathological heartwood.
Preparing Bolts, Flitches for Veneer Cutting
Nineteen bolts for rotary cutting were sawed from the logs of the 1946
(13) and 1947 shipments. Two bolts, two flitches for flat-slicing,
and four flitches for quarter- slicing were sawed from the 1956
shipment of logs. All bolts were about 4 feet long. The flitches
were about 6-1/2 feet long.
One bolt was cut at room temperature. The other bolts were heated
in hot water at various temperatures from 120* to 210* F. Veneer
of good quality was cut from bolts heated at 150* F. Heart checks,
end checks, and ring shakes tended to open excessively in bolts that
were heated higher than 160' F.
The flitches were heated in hot water at 180* F. without incurring
any defects. Veneer of good quality was sliced from the flitches.
The approximate heating times required for conditioning 8-foot tanoak
bolts of various diameters in water at 160* F. to insure a tempera-
ture of 140* F. at a core diameter of 6 inches are as follows (4):
Log diameter Heating time
In. (Hr.
I? lz
24 54
30 81
2 The logs were obtained through the cooperation of the Pacific South-
west Forest and Range Experiment Station, Berkeley, Calif. and
the Simpson Logging Company.

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The approximate heating tinies required for (1-onditioning 8-foot flitches
of various end dimensions in water at 180 F. to insture a temperature
of' 1600 F. at the flitch center are as follows (,1)-

Average end dimension
of flitch
(In.)

Heating tiine
(Htr. )

The data in these tabulations are based on an assumed starting tempera-
ture of 70 F. If the wood is colder, additional heating time is
required.
Veneer Cutting
Rotary Cutting
The lathe settings listed in table 2. were satisfactory for cutting veneer
of good quality. The heartwood and sapwood cut equally well with
these settings.

Most of the veneer was smooth and uniform in thickness.
checks were shallow in 1/16 inch and thinner veneer, but
knife checks appeared in the 1/8-inch-thick veneer.

The knif e
fairly deep

The surface and end checks in the bolts from the 1947 shipment
caused the veneer to split severely. The knots cut smoothly but
often nicked the lathe knife. Veneer containing tension wood (10)
was often slightly fuzzy.
Slicing
The slicer settings presented in table 3 were suitable in most cases
for cutting veneer of good quality. Many sheets of veneer contained
both sapwood and heartwood.

Report No. 1766-15




The quarter-sliced veneer was smooth. Some of the 1/8-inch veneer,
however, had fairly deep knife checks. The quarter-sliced veneer
also had fairly prominent ray ''flecks. "
The flat-sliced veneer 1/20 inch thick was usually smooth enough for
use as face veneer. Flat-sliced veneer 1/8 inch thick was moderately
rough in half of each sheet.
In general, smooth veneer was cut when the angle between the ground
face of the slicer knife and the wood rays was less than 90* (7). Rough
veneer was cut when this angle was greater than 90'. Veneer con-
taining tension wood was often slightly fuzzy.
Veneer Drying
The schedules used to dry the veneer in a mechanical roller-conveyor
type of veneer dryer are shown in table 4. Most of the veneer was
sapwood and dried satisfactorily. In general, heartwood veneer up
to 1/16 inch thick dried satisfactorily in a roller-conveyor dryer.
The sapwood and heartwood dried at about the same rate, but the
heartwood 1/8 inch thick often checked and collapsed. As a result
of these drying problems, most of the tanoak heartwood 1/8 inch or
thicker cut at the Laboratory was not suitable for use as face veneer.
Dried veneer tip to 1/16 inch thick was often slightly buckled, but not
enough so to prevent its use.
Splits present in the green veneer often widened and lengthened during
drying, but new splits did not develop. Most of the knots were inter-
grown and stayed in the veneer after it was dried. Upon being heated,
the wood darkened, especially in areas of short grain.
Surface checks developed adjacent to the rays when some of the flat-
sliced and rotary-cut veneer was dried. The checking was present in
about the same degree as in dried veneer of the true oaks.
?n
Tension wood (10) caused buckling in some of the veneer during drying.
Areas containing the gelatinotis fibers associated with tension wood
were usually darker than the typical wood, but most of the fuzziness
present in the green veneer disappeared after the wood was dry.

Report No. 1766-15




Tangential shrinkage was high, 0(Is .ij t I 5. 6 pcrc et.nt (d t i
green dim ensions, whcni th te v'll%'(l S i of 2 to 8 percent. Radial Sh11inl1, ;Igr :,'vot) 'Cd Ibout 6. <) l.( (1t (A' thc
green dimensions.
One-eighth-inch sapwoodt venecr, both rot ry- ut ,nd flt-sin :o, was
satisfactorily press-dried for use as flooring ().
Veneer Yields
Good yields of face-grade veneers were obtained from some of the bolls
that were rotary cut and from the flitches that were flat sliced. Much
veneer was degraded by surface and end checks that occurred in the logs.
Some degrade was caused by collapse that occurred during drying.
Other causes of veneer degrade were knots, holes and stains caused by
ambrosia beetles, decay, fungus stain, and tension wood.
Stains
Many of the bolts and flitches had stains associated with decay. O one
log, dark stains were present around the ambrosia-beetle holes.
The wet veneer developed a blue-black stain upon contact with iron or
steel. The stain, however, was easily removed by swabbing the wool
with oxalic acid (3). Complete removal of the acid with hot water was
necessary to prevent a pink stain from appearing where the acid haci
been applied.
The veneer sometimes turned a darker brown during drying. Tnoak
face veneers occasionally darkened during hot pressing of the plywood.
These discolorations can be kept to a minimum by using moderate
drying temperatures and cold pressing the plywood.
Gluing
Plywood panels of good quality were made with 1/20-, 1/16-, and 1/8-
inch tanoak faces and backs. Cores and crossbands consisted of t-noak

Report No. 1766-15




or yellow-poplar. Hot-pre'ssedI panels were made with a liquid phenolic
glue, a phenolic film glue, and with an extended urea glue. On the
other hand, a straight urea glue and a casein glue were used in making
cold-pressed panels.
Tanoak does not present unusual gluing problems (8), and good joints
can be expected with any of the conventional wFoodworking glues used
with good control of gluing conditions.
Interior Plywood Exposure Test
Some three-ply panels were made with 1/16-inch rotary-cut face veneers
and 1/8-inch rotary-cut cores. Several panels were hot pressed with
a urea glue, while the others were cold pressed with a casein glue.
All were finished with two coats of sealer and one coat of wax. These
panels were exposed for 1 month in a room at 80 F. and 30 percent
relative humidity, followed by a month in a room at 80 F7. and 80 per-
cent relative humidity. The cycle was repeated four times. After
this exposure, most of the panels were free of face checks or grain
raising. A few panels had incons-picuous hairline checks.
Tanoak Veneer and Plywood Flooring
Tanoak veneer 1/8 inch thick was press-dried (6) and installed over
a concrete office floor at the Laboratory. After several months of
use, this floor is still in good condition.
Plywood flooring blocks faced with 1/8-inch rotary-cut tanoak veneer
have been in service at the Laboratory since 1948, and have shown
excellent wearing properties.
The veneer flooring and the faces of the plywood flooring blocks were of
sapwood. The I1/8-inch heartwood was not suitable for faces because
of defects that occurred during drying.
Finishing
The plywood made with thin tanoak face veneers needed little sanding.
The press-dried flooring strips made from I/8-inch veneer required

Report No. 1766-15

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moderate sanding to rem~-ovc the renighne..s irregular shrinking in thickniess Some of the panels were finished[ with a gloss, while other panels were covered with two coats of sealer and
then waxed. The press-dried flooring strips were finished with filler,
two coats of floor seal, and wax.
Tanoak is a diffuse-porous wood, and has pores smaller than those in
the true oaks. The pores in tanoak, however, are larger than those
in birch, and consequently the wood should be filled if a continuous
smooth film finish is desired.
Appearance and Potential Use of the Veneer
Tanoak has the necessary properties for use as face veneer when it
is cut 1/16 inch or thinner. It has attractive color, and some of the
sliced veneer has good figure. Rotary-cut tanoak veneer is sorne-
what similar in appearance to rift-cut white oak. Sapwood veneer
1/8 inch thick appears suitable for use as veneer strip flooring or
for plywood block flooring. Small quantities of tanoak veneer have
been cut commercially for face veneers. The species is probably
best adapted to rotary veneer cutting.

Report No. 1766-15




Litcrature Cited

(1) Brown, H. P. Panshin, A. J. and Forsaith, C. C.
1949. Text. Book of Wood Technology, Vol. 1, McGraw-Hill Book
Co., Inc., N. Y.
(2) Davis, Edward M.
1947. Machining of Madrone, California Laurel, Tanbark Oak, and
Chinquapin. Forest Products Laboratory Report No. R1727.
(3) Downs, L. E.
1950. Bleaching Wood. Forest Products Laboratory Report
No. 1705.
(4) Fleischer, H. 0.
1959. Heating Ra)tes for Logs, Bolts, and Flitches To Be Cut into
Veneer. Forest Products Laboratory Report No. 21 49.
(5) Harlow, William M. and Harrar, Ellwood S.
1941. Textbook of Dendrology, 2nd Ed. McGraw-Hill Book Co.,
Inc. N. Y.
(6) Heebink, Bruce G.
1952. Veneer Flooring. Journal of the Forest Products Research
Society, Vol. 2, No. 3.
(7) Lutz, John F.
1956. Effect of Wood Structure Orientation on Smoothness of
Knife-Cut Veneers. Forest Products Journal, Vol. VI (11).
(8) 01lson, W. Z.
1955. Gluing Characteristics of Chinquapin, Tanoak, California
Laurel, Madrone. Forest Products Laboratory Report
No. 2030.
(9) Paul, Benson H., Dohr, Alfred W. and Drow, John T.
1955. Specific Gravity, Shrinkage, and Strength of Tanoak. Forest
Products Laboratory Report No. 2041.
(10) Pillow, Maxon Y.
1953. Effects of Tension Wood in Hardwood Lumber and Veneer,
Forest Products Laboratory Report No. R1943.

Report No. 1760-15




(11) Randall, C. A.
1956. Strength and Relatedt Properties of Taoak. .Journtial of
Forestry 51 (7).
(12) Roy, D. F.
1957. Silvical Characteristics of Tanoak, Forest Service, Cali-
fornia Forest and Range Experiment Station, Tech. Paper
No. 22.
(13) Schowalter, W. E.
1946. Exploratory Tests in the Rotary Cutting of Veneer From
Certain California Hardwoods. Forest Products
Laboratory Report WP-66.
(14) Torgeson, O. W.
1956. Kiln-Drying Schedules for 1-Inch Laurel, Madrone, Tanoak,
and Chinquapin. Forest Products Laboratory Report No.
1684.

Report No. 1766-15

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Table l.--Description of tanoak test logs

Log: Date

:Average :Length :Total :Average

:Average:Average :Average:
: eccen-:moisture:specific:
: tricity: content 2: gravity 3:
:of pith:::

Remarks

:Source

No.: of :diameter:
:veneer : inside :
:cutting: bark, :
: : small :
: : end :
: : In. :

:number: width
: of : of
:rings : sapwood
: mid- :
: len gdi "

Ft.

: In.

:In. :Percent:

1946

17-1/2 : 4

8-3/4 : 2-3/4

:Sonoma
: County,
: Calif.

70 :

....... :Ring shake; end checks.

24-1/2:

3-1/4

1947

150

0.54 :Severe end and surface checks.:H1umbolt
: : County,
: : Calif.

7

2: 1947 : 17 : 16-1/2: 150
3: 1947 : 15-1/2 : 17-1/2: 150
4: 1947 : 26-1/2 : 8-3/4: 150
5: 1947 : 16 : 8-1/4: 150

: 3 : 1

71 : .58 : ............. do ............... : Do.

: 6

: 5/8 : 83

: .57 : ............. do ............... : Do.

: 7-1/2 : 1-1/2 : 87 : .57 : ............. do ............... : Do.
: 5-1/2 : 1/2 : 58 : .55 : ............. do ............... : Do.

231:

1958

: 19 -1/2

166

1/4

.56 :End checks; bark-beetle :Sonoma
: damage; fire scar, ambrosia- : County,
: beetle damage; stain; decay. : Calif.

6

97 :

232: 19 58 : 17

: 10-2/3: 171

.55 :End checks.

: Do.

: 7 : 1/2 : 110

I-Age of all

logs in the 1947 shipment is estimated.

-Based on ovendry weight.
-Based on green volume and ovendry weight.




Table 3.--Slicer settings used to cut tanoak veneer
Veneer : Knife :Knife: Nosebar settings :Nosebar
thickness : angle :bevel:-------------------: bevel
: :Vertical:Horizontal:
..---------- ---------:: ------------
In. :Deg.-Min.: Deg-: In. : In. : Deg.

Table 2.--Lat iw 1, : ; Cd LO CULtedn ta c t( l, v i(r

Venleer: Kni fe : Knife" ,setcar ft t' -'
thickness : angle bevel.-----------------.. : bey( 1
: : Vertica 1: ilor izonta :
----------:-- ---- ---------------- -:- :-
In. :Dep,-Min. De In. n. :D~

1/24
(0.042)
1/20
(0.050)
1/16
(0.063)
1/8
(0,125)

: 90 45 :
: 90 45 :
: 90 35 :
:90 0
: 90 0 :
:

0.012 :

0.037

: 15
: 15
: 15

21 :

21 : .012 :

.045
.050

.015 :
.028U:

21 :
21 :

.115 :

1/20 : 90 30 : 22 : 0.030 : 0.045
(0.050) :

: 12

1/8 : 90 20 : 22 :
(0.125) :

.030 :

.115 : 12

Report No. 1766-15




UNIVERSITY OF FLORIDA
11111111111 tl 11 Elll ll 1111111111111 E 11111111
3 1262 08924 5020
Table 4.--Veneer drying schedules used and shrinkage values
determined for tanoak veneer
Veneer :Veneer dryer:Drying: Average : Average
thickness:temperature : time : shrinkage values :moisture
: ------------------: content
:Radial :Tangential:
In.------ :- F : Min. : Percent-: Percent
In. F. :Min. :Percent: Percent :Percent

1/24 :
1/20 :
1/16 :
1/8 :

250 : 7 :.......
250 : 13 : 7.3 :
250 : 15 :.......

7.7 2
13.5 : 6

12.5
13.7
18.6

: 8
: 8
: 8

250
320

8.1
5.8

Report No. 1766-15