United States

Department of

Agriculture Industrial

Forest Service

Forest Performance of

Products

Laboratory

Research

Paper

Powered Back-up

FPL 430 Roll for Peeling

Veneer
Abstract

Veneer log spin-out has been a continuing problem in

the plywood industry, contributing to increased timber

consumption and higher costs. To alleviate this

problem, a laboratory prototype powered back-up roll

(PBR) was designed and built by the Forest Products

Laboratory.

Because of satisfactory laboratory performance, a

commercial model of the Forest Products Laboratory

(FPL) PBR was installed in Boise Cascade’s Yakima

plywood plant. Operating under actual plant conditions,

the PBR has significantly reduced spin-outs. It has not

interfered with the normal veneer peeling operation,

and has been well received by plant personnel. The

payback period is estimated as less than 1 year.

This paper is the fourth in a series of four papers

describing the FPL powered back-up roll. The other

Research Papers are:

FPL 427 Influence of Chuck Design on Spin-Out Torque

in Softwood Veneer Peeling Blocks

FPL 428 Powered Sack-Up Roll-New Technology for

Peeling Veneer

FPL 429 Laboratory Performance of a Powered Back-Up

Roll for Peeling Veneer

-The use of trade, firm or corporation names in this

publication is for the information and convenience of

the reader. Such use does not constitute an official

endorsement of approval by the U.S. Department of

Agriculture of any product or service to the exclusion

of others which may be suitable.
Photo Supplement to Research Paper FPL-430

These photographs provide a ready reference on the Powered

Back-up Roll (PBR) in commercial use. The PBR helps

prevent or reduce veneer log spin-out by providing torque

to the surface of the logs. These photos of the PBR at

work were taken at Boise Cascade’s Yakima, Wash., plywood

plant, where this commercial model has been in operation

since October 1981.

The powerhead assembly is ready to be lowered onto the log.

Its two rollers assist the chucks in rotating the log against

the lathe knife. The powerhead is mounted at the end of

4-foot long arms which extend outward from a rotating

torque tube (A). At either end of the torque tube are lever

arms (B) connecting the tube to hydraulic positioning

cylinders (C). The cylinders raise and lower the powerhead

and hold it against the log during peeling.

Closeup of a hydraulic positioning cylinder shows a position

transducer (arrow), which helps control the position of the

powerhead. Also shown are the dual lathe chucks, with outer

chuck retracted.
Here the powerhead is in operation and the log is being

peeled. The arrow points out a shock absorber on top of the

powerhead that helps produce a smooth peel by dampening

powerhead vibration.

When peeling is complete, the powerhead is lifted off the

core, the spindles retract, and the core drops out.

Photographs courtesy of Boise Cascade

Published by the Forest Products Laboratory, Madison, Wis.
United States

Department of

Agriculture

Forest Service

Industrial

Performance of

Powered Back-up

Roll for Peeling

Forest

Products

Laboratory1

Research

Paper

FPL 430

October 1982

Introduction

Veneer

By

STEPHEN P. LOEHNERTZ, Research General Engineer

Spin-out occurs when the lathe chucks spin freely in

the ends of a veneer log. Some problems causing spinout are in the log–punky wood in the center, or a

hollow core. Another problem is overheating of the log

ends, which softens the wood. The general problem is

that more torque is required to turn the log than the

chucks can provide resulting in spin-out. Once it

occurs, a log cannot be peeled further for veneer.

The powered back-up roll (PBR) goes a long way

towards solving this problem by providing torque to the

surface of a log. This means that the chucks do not

have to do all the work. It also means that smaller

chucks can be used, resulting in a smaller core

remaining. This all translates into additional veneer

recovery, and savings of the timber resource.

The laboratory performance of a prototype PBR,

designed by the Forest Products Laboratory (FPL),

generated considerable industry interest. As a result,

FPL entered into an agreement with Boise Cascade

whereby a PBR was installed at their Yakima plywood

plant (fig. 1). The intent was to reduce the spin-out rate

with white fir logs. Table 1 lists the operating statistics

for the Yakima plant.

The PBR installed at Yakima was designed and built by

Premier Gear and Machine Works, and the controls

system by Lloyd Controls. The PBR became operational

in October 1981.

1Maintained at Madison, Wis., in cooperation with the University of

Wisconsin.

System Description

The major PBR components are the powerhead

assembly, positioning assembly, hydraulic supply unit,

and control system.

The powerhead assembly consists of two rollers, each

6 inches in diameter and 24 inches long, a

30-horsepower hydraulic motor, and a gear box (fig. 2).

The powerhead is mounted on arms extending 4 feet

outward from a torque tube mounted atop the lathe (fig.

3). The powerhead is raised and lowered by rotating the

torque tube by means of a lever arm at each end to

which a hydraulic cylinder is attached (figs. 4 and 5).

One cylinder has a built-in transducer which indicates

the position of the rollers at any time. Both the

hydraulic motor and cylinders are serviced by a

hydraulic power unit located off to one side of the lathe

(fig. 6).

Controls

Two types of controls are built into the system. The

first is the position control which holds the powerhead

against the log with sufficient force to provide traction

for the rollers. The position control circuit determines

the radius of the log by monitoring the knife position,

which indicates the location of the log surface. The

control unit then commands the hydraulic cylinders to

move the rollers to an imaginary point just inside the

log surface, the so-called “interference” position. This

creates a force between the rollers and the log. As the

log is peeled this force is reduced in order to avoid

pushing the smaller, more flexible core into the knife.

The second control matches the speed of the rollers to

that of the log, and maximizes the torque transmitted
Figure 1.–Boise Cascade Yakima Plywood Plant.

(M 150 896-28)

Figure 4.–View of powerhead (a) and one end

of torque tube (b). Notice lever arm

(c) and hydraulic positioning

cylinder (d).

(M 150 896-26)

Table 1.– Boise Cascade Corporation Yakima Plywood Plant

Annual Capacity: 125 MMSF (3/8 in.)

Production: 75% CDX, 15% Underlayment, 10% Misc. Ext.

Logs: Average Blocksize – 16 in.

Species – Douglas-fir (50%), White fir (50%)

Block Conditioning: Type – Hot Water

Soak Time – 10 to 14 hours

Temperature – 140° to 160° F

Additives – Wetting Agent Used

Peel: Douglas-fir – 1/8 in.

White fir – 1/8 in, 3/16 in.

Figure 2.–PBR powerhead assembly.

(M 150 896-17)

Figure 3.–View of powerhead (a) and mounting

arms (b).

(M 150 896-20)

from the rollers to the log. The speed-matching circuit

determines the surface speed of the log by combining

the knife position (radius) signal with the spindle rpm

signal. It also determines the roller surface speed from

the roller rpm signal. The two speeds are compared and

a difference indicates that the rollers are slipping. This

causes an error signal to be generated which

commands a servo-valve to adjust the flow to the

hydraulic motor, causing the rollers to speed up or slow

down as necessary. When the roller speed again

matches the log speed, the roller torque is maximized

as follows: The control unit monitors the knife position

and from that determines log size and the acceptable

roller torque. It then commands the servo-valve to

adjust the hydraulic pressure to the motor as needed in

order to achieve the correct torque.

Operation

The general sequence of events in the operation of the

PBR is as follows: First, the log is rounded up the

usual way without the PBR. Then, before the outer

chucks retract, the PBR is lowered onto the log with

the rollers already turning. The control system

maintains correct position, speed and torque output.

When peeling is complete, the powerhead is lifted off

the core, the spindles retract, and the core drops out

(fig. 7). The PBR in no way hinders normal operation of

2
Figure 5.–Closeup of hydraulic positioning

cylinder showing transducer

location.

(M 150 896-33)

Figure 6.–Hydraulic power unit.

(M 150 896-22)

the lathe. The operator still has a good view of the log

as it is being peeled, due to the compact design of the

PBR.

Installation and Startup

The PBR was installed in a Yakima plant in October

1981. It replaced the conventional nonpowered rollers

on the 8-foot Premier lathe. The installation did not

require modification to the lathe frame, and was

accomplished over one weekend.

Several problems occurred with the initial startup but

were quickly solved. First, there was a contaminant in

the hydraulic oil which caused a servo-valve to fail.

Second, one of the gears in the roller drive failed, and

was replaced. Neither problem has reoccurred.

Figure 7.–Lift-off of powerhead (a), and core

drop out (b).

(M 150 896-16)

After 1 week of running, a roller shaft failed where the

diameter was stepped down to form a shoulder for a

bearing. The step created a stress concentration which

led to the failure. A redesign eliminated this problem.

After 7 weeks of running, part of the coating on one

roller started to come off. It did not affect the operation

of the unit, but shortly thereafter, both rollers were

replaced. The new rollers have a different type of

coating which is reinforced with a cord material, as in

automotive tires. These rollers were still in service after

6 months, with no signs of trouble.

Test Program

A test program was jointly developed and conducted by

personnel from the Forest Products Laboratory, Boise

Cascade, and Lloyd Controls.

3
Yakima plant personnel documented the overall impact

of the PBR on the peeling process, such as spin-out

rate, veneer yield and core to stud yield. At this plant,

spin-outs cannot be cut into studs because they are

oversized for the stud mill.

Forest Products Laboratory personnel were on hand for

1 week of intensive data gathering to determine the

system-operating characteristics. These included rollertorque output, control functions, roller-coating

performance, and veneer quality. Data were recorded by

means of a 3-channel Esterline-Angus chart recorder,

and a Hewlett-Packard XY plotter. Similar

determinations had been made in the Laboratory for

the prototype.

Results-Yields

The PBR has proved very effective in reducing spin-out.

This is noted in table 2 which shows the change in

percent of logs which are peeled down to the core

without spin-out. The biggest increase is for the white

fir 3/16-inch peel. Improvements are also shown for

Douglas-fir, and white fir 1/8-inch peel, although these

are less prone to spin-out. Table 3 shows reduction in

the spin-out volume as a percent of total block scale.

Table 4 shows veneer and stud recovery increases that

should be expected from the spin-out reduction that

was achieved. These increases are 2 percent for veneer,

and almost 11 percent for studs.

Table 2.–Percent change of logs peeled to core without

spinout

Species peel

In.

Douglas-fir 1/8

White fir 1/8

White fir 3/16

Blocks to core size (5-3/8 in.)

W/O PBR W/PBR

. . . . . . . Pct . . . . . . .

95.9 97.4

87.1 96.3

56.9 72.8

Table 3.–Reduction in spin-out as a percent of total block

scale

Species peel

In.

Douglas-fir 1/8

White fir 1/8

White fir 3/16

Spin-out volume as pct

of total block scale

W/O PBR W/PBR

........Pct........

0.4 0.1

1.8 0.3

7.1 2.7

Table 4.– Powered back-up roll effect on product recoveries

Product W/O PBR W/PBR INCR(DECR)

_______

Veneer (msf/mbf)

Chips (bdu/mbf)

Studs (mbf/mbf logs)

2.50

0.534

0.090

2.55

0.499

0.099

Pct

2.0

(6.6)

10.9

Under normal market conditions the cost of the Yakima

PBR could be paid off in less than a year.

Results-Operating Characteristics

The data describing the operation of the PBR are

secondary in importance to the results just given, but

they do provide useful design information.

Torque Output

It was not possible to directly measure the torque

applied to the log by the PBR, so it was calculated

from measurements of motor pressure and log

diameter. The torque output of the hydraulic motor is

proportional to pressure. The torque actually applied to

the log is effectively multiplied through the PBR gear

box, and again through the ratio of the log and roller

diameters.

Representative torque curves are shown in figure 8.

They are similar for both white fir and Douglas-fir.

Comparing these data with results from the Laboratory,

it is estimated that the values shown in figure 8 are

approximately 25 percent of the total torque required to

peel these species. The remainder of the torque must

be provided by the chucks.

Controls

The normal force on the veneer log was calculated from

the measured pressure in the hydraulic-positioning

cylinders, taking into account the lever arm and adding

on the dead weight of the roller head. The value of this

force is approximately 1,400 pounds for a core diameter

of 5-3/8 inches. The magnitude is somewhat higher at

larger diameters.

Simultaneous recordings were made of roller and log

speeds to determine if roller slip was occurring. None

was detected. This means that either the control

system is doing its job of preventing slip, or that the

rollers have very good traction and are not likely to slip

with the levels of torque and the normal force involved.

Figure 8.–Torque provided by PBR forpeeling

white fir and Douglas-fir.

4
Veneer Quality

Veneer quality was determined visually by inspecting

the surface, and by measurement for uniformity of

thickness. The veneer surface did not appear to have

been affected by the powered rollers. There was no

scuffing or marking, or any indication that the rollers

had contacted the log.

The veneer thickness was fairly uniform, typically

varying by no more than 0.006 inch across the width of

an 8-foot sheet. Near the core, however, this variation

increased to as much as 0.020 inch and the surface

was considerably rougher. This is considered fairly

typical for core veneer. Overall, it was judged that the

PBR did not adversely affect veneer quality.

Roller Coating

The roller coating performed quite well during the test

program. The rollers did not slip or mark the veneer,

and stayed clean. Initially, there was concern that the

coating would load up with pitch, but this did not

happen. The rollers appeared to be self cleaning. As

mentioned earlier, one of the roller coatings began to

wear off after 7 weeks of operation, but a new material

replacement is still in service. This is very encouraging,

especially since little development effort went into

3.0-6-12/82

evaluating different coating materials. Undoubtedly,

preventing roller slip is a big factor in prolonging the

life of the coating.

Discussion

The PBR program is a good example of technology

transfer from the research laboratory to industry. It was

made possible by cooperation between the Forest

Products Laboratory, Boise Cascade, Lloyd Controls,

and Premier Gear.

The PBR has proved itself in reducing spin-out, and

increasing veneer and stud recovery at the Yakima

plant. It has not interfered with the normal veneer

peeling operation, and has been well received by plant

personnel.

There are many refinements which undoubtedly can,

and will be made to this basic design in the future as

industry becomes more familiar with it. Boise Cascade

feels it would pay for itself in less than a year in a

normal market. Indications are that this new

technology for peeling veneer will eventually be

implemented industry wide.

U.S. Forest Products Laboratory

Industrial Performance of the Powered Back-up Roll, by

Stephen P. Loehnertz, Madison, Wis., FPL 1982.

6 p. (USDA For. Serv. Research Paper FPL 430).

Describes the installation, startup, and testing program of the

powered back-up roll for peeling veneer in operation at an industrial

plywood plant.

Keywords: Powered back-up roll, veneer peeling, spin-out,

veneer yield, veneer quality, resource recovery, chucks, core size,

rollers, torque output.

5
U.S. GOVERNMENT PRINTING OFFICE: 1982-554-030/ 21