HARVESTER HEAD
DAMAGE
WHAT IS THE COST?
A GUIDE to ASSIST OPERATORS
to MINIMISE VALUE LOSS
HARVESTER HEAD DAMAGE
WHAT IS THE COST?
Prepared for
SWI LIMITED
by
Don McConchie - Wood Quality Focus
CONTENTS
PURPOSE OF THE GUIDE
2
INTRODUCTION
2
CHARACTERISTICS OF
LOG DAMAGE
3
LOG DAMAGE ASSESSMENT
TECHNIQUE
8
CHARACTERISTIC DAMAGE
IN SAWN BOARDS
11
VALUE LOSS
17
BASELINE DATA
18
HOW CAN OPERATORS MINIMISE
HARVESTER HEAD DAMAGE?
20
CONSEQUENCES
22
CONCLUSIONS
24
Further Reading
25
Acknowledgements
25
Disclaimer: This Guide is intended by SWI as an
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PURPOSE OF THE GUIDE
This guide has been produced to help raise
is presented to standardise damage assessment
INTRODUCTION
With the emphasis on safety and the increasing
training can minimise damage,
the severity of damage - logs with large
branched whorls directly above the pruned
log are more likely to be damaged to a
greater extent,
and/or less well maintained machines
and the capacity for adjustment of feed
industry to be able to readily determine the
severity of damage and establish a link to value
CHARACTERISTICS
OF LOG DAMAGE
Firstly incisions of various shapes (straight,
thumbnail, spike or pineapple) generally to a
depth up to 3 cm caused by the drive roller
teeth, and tears or gouges caused when the
stem stops moving through the harvester head
when the depth of damage is measured,
to the two faces of contact along the length of
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4
the log and are usually <1 cm deep, although at
rerun to remove a large whorl above the pruned
rollers is classed as Low
or occasionally Moderate
Low
the teeth incisions, more localised and is usually
This deeper damage can occur when the
harvester head jambs, for example and most
commonly at a large whorl at the top of the
pruned log causing the delimb knives to gouge
The stem must be passing through the harvester
measurement the knives can gouge towards
the log can also occur when a grapple grabs the
type of damage accounts for many Moderate
Severe
Moderate.
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Moderate.
Moderate.
Severe.
Damage which is generally bruising and incisions
to the surface and immediate subsurface of
log damage therefore results in the loss of high
clearwood, along with the normal level of wane
when ripping to width or docking, will reduce
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8
LOG DAMAGE
ASSESSMENT TECHNIQUE
each log is assessed for the depth of damage
<1 cm Low, 1-3 cm Moderate and >3 cm Severe
To measure the depth of damage a normal single
plane screw driver was used with coloured
into damage marks either roller teeth incisions
tape boundary), and
The split of <1 cm and >3 cm was arrived at
large data set of measured logs showed very
is the depth of damage generally allowed in
the more numerous and lesser depth of damage
harvester head damage has not previously been
number of logs may in fact be worse than
Low
be Moderate or Severe and a Moderate
Severe
The next series of photos show the high level
of bark removal and the presence of grit on
the log surface and within gouges typical of
removal is seasonal in nature with less removed
during the winter period of dormancy or
Low and Moderate
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Moderate
CHARACTERISTIC DAMAGE
IN SAWN BOARDS
For the study to develop the log assessment
face boards transferred from the mill prior to
ripping which could have removed much of
the damage along with the wane, and docking
each board was then assessed by measuring the
width if correctly ripped for wane and what the
width would need to be reduced to, to remove
to board feet using the appropriate measuring
In the studies undertaken, the percentage loss
of Clears ranged from no loss for 5 logs to a
maximum 35% loss for a log classed as Severe
A greater depth of cut occurs at the large end
due to normal log taper and hence considerable
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Boards can also show signs of damage but log
The following photographs show examples
of typical harvester head damage on boards
loss of Clears
Low
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VALUE LOSS
A number of factors contribute to loss of value
- log diameter and shape,
and within batches of logs the loss of Clears for
opening face boards could fairly be regarded
as 5%, 10% and 24% for Low, Moderate
and Severe
a 200 mm opening face cut then for every 1 cm
depth of damage over and above the normal
Clears
When a millgate price for Clearwood of $700/m3
was used, the loss in value/m3 of logs processed
Low
Moderate and
Severe
Note:
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BASELINE DATA
Applying the
this Guide, a sample of 1125 logs were assessed
at mills and logging sites in both the North and
logs, the majority of logs fall within the Low
severity class (69%) with a similar breakdown of
producing the Tenon pruned logs was unknown,
but assumed to be variable as logs from a wide
only 2-4% of logs were assessed as Severe
Where the volume of pruned logs processed by
harvester heads is known, results indicate there
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Kaituna
Nelson
Taranaki
Tenon
TOTAL
Location
69
68
78
70
62
3
2
4
4
3
29
20
26
34
28
Percentage of Logs by Severity Class
Low
Moderate
Severe
Harvester Head Damage Assessment by Log Severity Class
337
272
154
362
1125
No. of
Logs
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HOW CAN OPERATORS MINIMISE
HARVESTER HEAD DAMAGE?
In discussion with machine harvester
manufacturers and operators within the
trained on all aspects of the use of a
- carry out regular
and any other maintenance as and when it
- when replacement
or recommended by the appropriate
- only run the head down the tree
to length, every pass of the harvester head
over the stem creates damage even if only
- delimb knife pressures to be set correctly,
use the “knife pressure based on
- delimb knife edges to be correctly
sharpened, excessively worn knives should
Drive rollers - wear to be monitored, and
- drive roller close pressure to be set
- to be entered correctly
into the harvester head computer and
all sensors and encoders to be calibrated
accurately this will avoid unnecessary
reversing on the the stem to achieve
“Find End” sensors - must be used before
undertaking any form of log making or length
bucking, to avoid unnecessary “biscuit “
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- trained operators
can listen to the machines they operate and
The result of worn feed rollers is that the
physical length of the teeth decreases and the
the stem and gouging if the reason for slipping is
incidence of Moderate and Severe
Excessive pressure will cause deeper tooth
Moderate and Severe
Running dull delimb knives usually does two
This may increase the chance of Moderate
the harvester head with constant stopping
head thinks the diameter is larger than it
actually is, it will apply excessive pressure while
This also applies in reverse when the diameter
is actually larger than calibrated, lower pressure
increase in Moderate and Severe
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CONCLUSIONS
By using the suggested standardised assessment
data from across the industry to monitor
similar machines
due to harvester head damage to be more
FURTHER READING
Grapple processor
ACKNOWLEDGEMENTS
Jason Huitema at Waratah and Chris Hancock
at Woodsmanpro for their advice regarding
We also thank Bernie Schluter at the Kaituna
Mill for organising access to logs for assessment,
and Graeme Young and Derek Gwynne of Tenon
for access to logs for assessment and assistance
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