This glossary of terms is designed to help you.
We are keeping all of this information on a single web page, so
that you don't have to load a different page for each letter of
the alphabet, etc. If you cannot find what you are looking for,
please let us know. (info@irishwoods.com).
Simply find the word you are looking for in the
table below and click on it to find out more!
Air
Drying: Also known as seasoning. Air
dried timber has been allowed to dry in the open air or under cover
until it is consistently dry throughout the piece of timber. (i.e.
not just dry on the outside, but also in the centre). The boards
are separated by "stickers" which
allow the air to circulate around all surface of each board.
In Ireland, we can air dry timber to moisture
levels of around 17 to 22% MC (moisture
content), depending on the time of year, drying conditions and
storage (in the open/under cover). For furniture making and many
other uses, timber generally needs to be kiln
dried, to reduce the moisture levels still further . (See Moisture
Content (MC) for further information)
(Also see the "What
We Do" section of our website, which gives more information
on all of the processes involved in producing timber).
Annual
Growth Ring: Every year a tree expands it's diameter with a
layer of fresh growth below the bark (see cambium).
These layers are visible when a tree is felled, as concentric rings
of alternating dark & light wood. The different colours are
caused by the difference in the nature of the cells produced during
the growing season. By counting these rings it is often possible
to count the number of years that the tree has been growing for,
and hence its age. When a log from a tree is sawn, these rings appear
longitudinally as the grain of the timber.
Angiosperm:
The botanical name for the group of trees that are broadleaved.
B
Back
Sawn: This is where timber is sawn so that the growth rings
are almost parallel to the face of the board.
Bark
Pocket: Bark that has become trapped inside the tree as it has
grown, and which can therefore appear in the timber sawn from that
tree, often as a dark coloured and relatively soft.
Beam:
A large piece of timber, usually sawn square or rectangular in cross
section. Beams are often cut from the centre of a log, to maximise
structural integrity. Beams support loads mainly by their internal
resistance to bending.
Bevel: A tool
used to make a rounded or inclined/smoothed/patterned edge along
a square edge (which is also called a bevel). Also, see Router.
Birdseye/
Bird's Eye: Circular markings on the surface of a board which
add to the decorative value (especially in sycamore and maple).
They look like small eyes.
Biscuit
Joint: A method of joining two pieces of wood together, usually
along the edges. A slot is "scooped" out of the side of
each board (about 2 to 3" wide) and a piece of beech (called
a biscuit) is glued and inserted. The two boards are then clamped
together, with glue along the edges. The biscuit holds the wood
in place while the glue dries. The water from water based glues
causes the biscuit to swell, which allows it to get a very tight
grip on the pieces of wood, creating a good strong joint. (See also
Lap Joint).
Bleeding:
If there is sap/resin in the wood - particularly air dried softwoods,
and especially through knots - it is (by it's nature) a liquid...
and it can therefore move. This can cause weeping through the surface
of the wood, including through varnishes.
Blue
Stain (Sap Stain): When timber is sawn and stacked with stickers
for air drying, the wood can have a very high moisture content.
The timber contains fungal spores that it has been gathering during
growth. Occasionally the fungal spores "activate" in the
wood while it is still damp. This can weaken the structural strength
of the timber (the start of the rotting process). As the boards
dry out the fungus cannot thrive. Once air dried (less than 22%),
this process stops. In several cases, this process can produce a
stunning effect on the look of timber, called spalting,
especially in beech. The colours produced can vary, but is usually
black with blue, red and green variants occasionally seen.
Board:
A piece of sawn timber. Boards are sawn as square
edged, waney edged or through-and-through.
Boards vary in thickness, usually from 1" to 3", although
thicker sections can be sawn for specific purposes, such as for
mantelpieces or woodturning and carving.
(Also see the "What
We Do" section of our website, which gives more information
on all of the processes involved in producing timber)
Book Match/ Bookmatch:
If a board is split in two and opened like book, the result is two
asymmetrically opposite grain patterns facing each other. At the
Lisnavagh Timber Project, all of our boards are numbered as they
come off the saw bench which means that we can reunite "neighbouring"
boards for bookmatching.
Bow:
Boards sometimes bend, usually soon after sawmilling. This can be
caused by bad stacking of the timber, or perhaps an inherent stress
in the grain of the timber which might be due to the way the tree
grew.
Boxed heart:
The central core of the tree (the "pith")
can be quite soft timber. This can be "boxed" in or concealed
by normal, harder wood. Boards like this might split
or warp more often than other boards.
Broadleaves:
Trees are grouped in several ways such as by the leaf shape (broadleaf/conifer),
timber (hardwood/softwood) or whether they loose their leaves in
winter (deciduous/evergreen.) Broadleaved trees are known botanically
as "angiosperms" and have wide
flat leaves (as opposed to conifers which have long thin needle-type
leaves. The timber is usually, but not always, hardwood timber,
and the trees are also usually, but not always, deciduous. Examples
of broadleaf trees include oak, ash, beech, elm, birch, chestnut,
cherry and lime. There are many more.
Burr: (In America
this is called "Burl") Occasionally trees have
wart-like growths up the trunk and/or branches. These are basically
where a large number of dormant budding points for twigs, or points
of epicormic growth have grown on top of
each other to cause a random looking swelling. The timber underneath
is not straight grained timber as one would see in a "normal"
board. When sawn though, the timber has swirling patterns of colour
and grain which are extremely eye-catching and interesting to the
observer. The wood has wonderful figure, and
as a result, burred timber is highly sought after by all users of
timber, especially woodturners and specialised furniture makers.
C
Cambium:This
is thin layer of cells that form between the bark and the sapwood.
Each year, new bark cells are formed on the outside of the layer
and new sapwood cells are formed on the inside. It is this growth
that creates the alternating light and dark rings, called annual
growth rings.
Case-hardening:
When timber dries it shrinks slightly, but if the centre of a piece
of timber is still wet when the outside has completely dried, it
will force the outside to stretch around the relatively swollen
centre. This causes stress between the inside and outside parts
of timber. The timber may not seem to have suffered, but when it
is planed, resawn, or machined in some way, the stress can cause
warping or splitting.
Case hardening occurs where timber is dried too rapidly.
Cat's
Paw: Small knots in the timber which have
the look of a cat's paw print. This is a feature valued highly by
furniture makers and is found in hardwood timber, especially oak
(called pippy oak) and elm. Cat's paw causes
little or no structural instability.
Cellulose:
The cells of wood are primarily made up of cellulose, which is a
very strong carbohydrate.
Check: If the
outside of the timber dries (and therefore shrinks) a lot quicker
than the inside, it can mean that small shallow cracks occur
on the outside of board, in line with the grain. Checking of timber
is not the same as splitting. Splits tends
to go right through the board and occurs singly, or in small numbers.
Check is usually a few millimetres deep, and often appears in clusters.
Collapse: If
timber is dried too much, cells can collapse, or flatten, causing
a rippled effect on the surface. The structural stability of the
timber is reduced as a result.
Compression
failure: If timber has had pressure along the grain (i.e. "end-on")
it can cause the fibres of the wood to buckle and deform. It can,
for example, occur where a tree has bent over. Compression failure
causes ripples to appear in planed timber.
Conifer: A grouping
of trees (botanically known as gymnosperms) with needle or scale-like
leaves (e.g. pine, fir, spruce, cypress). Most are evergreen trees,
and most provide softwood timber.
Cross-cut:
A cut across the grain. (i.e. sawing the end off a board
is crosscutting it).
Crotch wood:
Just below where a tree forks, the grain spreads in a fanlike pattern
which is visible when the timber is sawn. It is highly sought after
by wood turners.
Cup: Due to existing
stresses in a piece of timber it can "cup", especially
when drying. The board is slightly U-shaped when looked at end-on.
Cup shake:
Where the timber splits around a growth ring - also known as Ring
shake.
D
Decay:
The rotting or decomposition of wood initiated by fungi. The fungi
break down the (otherwise indigestible) wood into a softer, lighter
material which hundreds of species of insects are then able to make
further use of. In woodland, other animals, such as woodpeckers,
may then also become involved, searching for the insects, and causing
further injuries to the tree in the process, thus hastening the
rotting process further. Decaying wood loses strength, weight and
colour.
Decking: A timber
platform surface (for example for pedestrian/vehicular access across
a bridge, or outside a house as a raised amenity.
Dehumidifier
Kiln: A kiln which dries timber by way of
heat (perhaps 40° C) and dehumidification. Such kilns take slightly
longer than many other types of kilns to dry timber, but have the
advantage of low capital investment & running costs and can
result in less damage to the timber being dried.
(Also see the "What
We Do" section of our website, which gives more information
on all of the processes involved in producing timber).
Dowel: A round
length of wood (or, less usually, metal) used (typically) to join
two pieces of timber. A hole is drilled into each piece of timber
and the dowel inserted into both pieces, usually with glue.
Doze: A phrase
used to describe timber that has started to decay.
The timber is pale looking, light to handle and soft enough to be
indented by pressure from a thumbnail. Dozed wood is useless to
woodworkers.
Drying: The removal
of moisture from a piece of timber. See Air
Drying and Kiln Drying.
Durability:
A phrase to describe how resistant to decay
a piece of wood is.
Dutch Elm
Disease: A fungal disease (Ceratocystis ulmi) which effects
elm trees. The fungus is transmitted from tree to tree by bark beetles.
Originally discovered in Holland in 1919 - hence it's name. It was
in England by 1927, but in the 1960s a more aggressive strain took
hold (coming from N. America) and wiped out half the elms in England
by the mid-seventies. The disease is fatal and takes only a few
weeks to kill even a large tree, apparently by blocking the vessels.
Wych elm (Ireland's native elm) is apparently more resistant to
the disease.
E End Grain:
The grain that is visible at the end of a board, where it has been
cross cut.
Epicorm/Epicormic
growth: Small branches on the sides of a tree that have grown
from adventitious buds. The twigs start to grow, but die back, perhaps
due to a lack of light? This growth causes "mini" knots
to appear in the wood beneath and can result in highly figured timber
which is prized by wood workers and furniture makers. (See also
cat's paw and burr)
Equilibrium moisture
content (EMC): The moisture content
of wood which has reached a steady balance with the immediate environment
and where the relative humidity
and temperature of the air is constant.
Exotic: A description
used for non-native trees. That is, trees
which have been introduced into a country, usually by man. A tree
can only be called "exotic" in a country where it is not
native - so, for example, an exotic species in England could be
a "native" species in Ireland (e.g. the Strawberry Tree),
and vice versa (e.g. Beech).
Extraction:
This is the removal of felled trees or logs to a more accessible
area on edge of a wood where they can be collected (by a lorry,
for example). Methods of extraction include winching, mechanical
towing, towing with ponies or using a forwarder.
F
Face: The widest
surface of a piece of timber.
Fibre Saturation Point
(FSP): When timber is drying out, water evaporates from the cell
cavities first, and then the cell walls. The point at which the
free water in the cell cavities has been lost, but the bound water
in the cell walls remains is called Fibre Saturation Point, and
the moisture content (MC) of the
wood is typically between 25% & 30% at this stage. By taking
the moisture content below FSP the timber will shrink in size.
Fiddleback:
A wavy or ripple effect on the grain, typically in sycamore and
maple and often used for the backs of violins and other musical
instruments - hence the name. Also known as Tiger Stripe.
Figure: The word
used to describe the features and patterns of a piece of wood and
taking into account growth rings, medullary rays, grain, knots,
catspaw, burr, colour and anything else that affects the "look"
of the piece.
Fingerjoint:
The joining of two pieces of wood where the ends of the pieces are
cut to form wedge-shaped fingers which are then bonded with wood
glue.
Finishing: The
processes (usually sanding, polishing and perhaps oiling) that are
carried out once the basic structure of the wooden item is completed.
Fissure: A generic
term covering checks, splits, cracks, honeycomb and shakes along
the grain or rays.
Forwarder:A
forwarder (such as the one pictured) is used to extract
timber from the wood or forest to the roadside or some other suitable
point where it can be collected by a lorry. Forwarders can have
tracks or large rubber wheels, and these allow them to "roam"
in woodland, travelling over tree stumps and brash and with a greatly
reduced chance of getting bogged down in wet ground.
Fungi:
During the life of a tree, many types of fungal spores are continuously
getting into the trunk and branches, but are (for the most part)
harmless while the tree is healthy.
The spores enter though the roots, or damaged
bark, broken branches, etc. The spores generally cannot cope with
the high moisture content of the wood in a healthy tree, and only
activate when the wood partly dries out or when the tree is dead
or it's defence systems are unable to prevent activation of the
spores. Wood can dry out when there is a drought, or there is an
injury to the tree.
When the spore is activated, a mycelium is
produced which travels though the the sapwood, heartwood and/or
just under the bark (see photo of mycelium under bark of pine).The
only visible part of the fungus is generally the mushroom type growth
which appears on the outside of the tree or wood - this is the reproductive
centre of the fungus.
In some species, for example beech, the activation
of the fungal spores, and spreading of mycelium, causes discolouration
of the timber before the timber starts to soften. This is called
spalting, and the timber from spalted wood
is highly sought after by wood turners and other users of wood.
G
Glulam: Structural
timber that is made up of several smaller sections of timber that
are laminated together.
Grain: The main
fibres in wood, as arranged in the annual
growth rings, are referred to as the grain. Cuts of timber are
usually described by referring to the grain - e.g. across
the grain (cross cutting), or along the grain (as in ripping).
The density of grain is often used as a description for the appearance
of timber (e.g. wavy grained, close grained or open grained).
Green timber:
Freshly felled or sawn timber which has not yet dried out at all.
The moisture content will be in excess
of the Fibre Saturation Point (FSP), and fairly
consistent throughout.
Hardwood: This
is a botanical description of timber, rather than a specific
evaluation of hardness of timber. Generally, hardwood timber is
from broadleaved tree species. There are
some "softwoods" that are harder than "hardwoods",
but not many. (Also see our page on timber
densities)
Heartshake:
A split in the timber that runs though or from the centre of the
log towards the outside, crossing the growth rings. It can be caused
by a tree landing too hard when it comes down.
Heartwood:
This is the timber at the centre of the tree - between the pith
in the middle and the softer sapwood towards the bark. As the tree
grows & thickens, the cambium & sapwood are regenerated
towards the edge or bark of the tree, leaving behind rings of fibres
towards the centre which no longer need to carry nutrients or substances
(sap). These fibres alter to become stronger and resistant to decay
(and darken in colour). It is this hard material that gives trees
such significant structural reinforcement at their centre that they
can gain such notable heights.
High speed steel (HSS):
This is about 6 times harder than (normal) carbon steel. HSS tools
should be ground on a 'white' (aluminium oxide grinding wheel).
Honeycomb:
This is a serious problem, particularly in oak. Honeycombing is
caused when the inside of a board has a relatively high moisture
content, while the outside is being dried too rapidly. The result
is that the outside "sets". At this stage the outside
of the board will not shrink any further. The core of the board
then starts to dry, but, because the outside is set (or case
hardened), the inside starts to split apart as it tries to shrink.
Gaps open up in the wood inside the board and they tend to follow
the medullary rays, rather than the grain of
the wood. The result is a board that looks fine... at first. However,
when the timber is planed to below the case hardened surface, the
cracks/cavities inside the board become visible. It is said that
if the moisture gradient exceeds
6%, then honeycombing is more likely to occur.
I
Irregular grain:
Refers to grain that is not straight - for example, grain that bends
around knots or twists.
J
Jamb: The piece
of wood that runs up the side of an opening for a door or window.
Joinery: A term
to describe the creation of fixtures, or the fixtures them selves,
in buildings including doors, windows, cupboards, etc.
Joist: A beam
of timber that is used to support (usually) a floor or a ceiling
and which rests on a loadbearing wall's wall plate or some other
support. Sometimes joists are incorporated into the design of a
house so that they are visible and form a feature of the design.
K
Kerf: The cut made
by a saw.
Kiln: A chamber
used for drying timber down to a required Moisture
Content (MC). There are several different types of kiln, but
they all work on the principle of artificially controlling the temperature
and humidity in a way that reduces the moisture content as consistently
as possible throughout each piece of timber. See Dehumidifier
kiln
(Also see the "What
We Do" section of our website, which gives more information
on all of the processes involved in producing timber).
Kiln Drying:
Artificially drying timber in a kiln using controlled levels of
heat and humidity in order to reduce the Moisture
Content (MC) to a required level.
(Also see the "Practices"
section of our website, which gives more information on all of the
processes involved in producing timber).
Knot: An area of
wood which was originally part of a branch growing from the tree,
but which has subsequently become incorporated into the main stem
as it has grown and enlarged. In a board, most knots are seen in
cross-section. Whilst knots can be regarded as features, depending
on their nature, they are areas of irregular
grain which can reduce the strength of the timber. Knots are
usually darker in colour than the surrounding wood. An Open Knot
is a knot where the substance of the wood has either opened up as
a crack or dropped out completely. A Closed Knot is a knot
where the substance of the wood is contiguous with, and fixed to,
the surrounding material. (Also called a Sound Knot or Tight Knot).
See also Cat's Paw.
L
Laminated wood:
Several pieces of wood glued or fixed together to form a larger,
stronger piece.
Lap
Joint: A method of joining two pieces of timber by partially
overlapping them. This is done either by literally overlapping the
two pieces and fixing them together (with glue, screws, etc.), or
more neatly by cutting a rebate along each piece to be joined and
then fixing them together. (Also see Biscuit
Joint and mortise and tenon and
Tongue& Groove).
Lignin:
The "mortar" between the cells in wood. Lignin is the
second most abundant constituent of wood.
Lumber:
Another word for timber, principally used in North America.
Medullary rays:
These are groups of storage cells that run from the centre of the
tree to the cambium (under the bark). In oak, for example, they
can be very pronounced, especially in quarter-sawn
material, and are considered a feature.
Moisture
content (MC): The percentage of the weight of a piece of wood
that is water.
The original (and possibly still the most
reliable) method used to determine MC is to weigh a sample of the
wood before and after drying it out thoroughly in an oven. The difference
in the weight measurements is the water that has evaporated off
during drying. Simply by dividing the weight of the water by the
weight of the wood before drying, the percentage of water in the
original sample (i.e. the moisture content) is determined. More
usually moisture meters are used, and the best results are achieved
using meters with a hammer probe, where the needles of the meter
penetrate the wood to get readings at the centre of the piece.
The MC of timber is usually very important.
Many uses of timber require the timber to be sufficiently dry throughout,
and this is measured as %MC. For example (in Ireland at least) construction
timbers usually need to be dried down to 20%MC, wood for furniture
to 10-12%MC and floorboards, where under-floor heating is installed,
down to 6%MC.
When a tree is initially felled, alive, it
can have an MC reading of perhaps 100%. Most construction timbers
are kiln dried immediately as big sawmills have a very large turnover
and cannot wait for the timber to air dry. By air
drying timber under cover, MCs of 17 to 22% are easily achieved
in Ireland (being lower in summer than winter). The rule of thumb
is that it takes 1 year for 1" hardwood timber and 2 years
for 2" hardwood timber, although this depends on species, weather
conditions and storage conditions. To dry timber further than this
requires a kiln.
Moisture
Gradient: This is the variation in moisture
content from the centre of piece of wood to the edge. For example,
a piece of wood which is 23%MC on the outside and 28%MC at the centre
has a moisture gradient of 5% (i.e. 28 minus 23). A high moisture
gradient might occur in timber that has part air dried, for example.
When kiln drying, high moisture gradients (6%+) can cause serious
problems, especially with oak, and can result in case
hardening and/or honeycombing of the
timber.
Moisture Meter:An
instrument used to determine Moisture Content (MC). In order to
measure the MC of the inside of a piece of wood, a hammer probe
is used. The two pins of the hammer probe penetrate the wood to
a required depth (usually one third of the depth of the sample being
tested).
Mortise
and Tenon joint: A method of joining two pieces of timber. In
one piece a slot is formed (the mortise/mortice), and in the the
other piece a key to fit the mortise is cut (the tenon). The tenon
should fit snugly into the mortise to make a firm joint. These joints
are usually secured using wood glue and/or other pieces of wood
such as dowels.
N
Native: A native
species is one which is indigenous to a country. In other words
it has not been introduced from abroad. However, labelling a species
as "native" can be controversial, as most of the species
in any country have been introduced from another country at some
point in time, however long ago, and not necessarily by man. Or,
to offer another argument, seeds from monkey puzzle trees have been
found in the soil under Lough Derg (from beefier the Ice Age), so
does this mean the monkey puzzle is one of our native Irish trees?!
Natural
Regeneration: This occurs when seedlings grow without any direct
assistance from humans. It can start from a seed or from the suckers
of another tree. Seeds are carried by animals, birds or the wind.
In many woodlands, natural regeneration is now encouraged, especially
where the trees themselves are of a good provenance (genetic quality)
The birch pictured above are in
one of our woodlands here at Lisnavagh.
They naturally regenerated in a wood that was planted with sitka
spruce.
The spruce were not doing well, and were thinned out to let the
birch grow on.
It was a good decision, as the wood is now regarded as one of the
finest stands of birch in Ireland
O
Olive Ash:
Older ash trees can develop a stained heartwood. Compared to the
cream colour of ash in younger trees, olive ash is a dark brown
colour.
Open Grain:
A wood that has large pores is called open grained.
Oven Dry Weight:
The weight of a piece of wood after all of the available water has
been evaporated off. This is done in an oven at 100 to 105°C.
The Oven Dry Weight can be compared to the weight before drying
to give a very accurate measurement of the Moisture
Content (MC) of the undried wood.
P
Palmate: Leaves
that have lobes shaped like the fingers of the hand, e.g., Horse
Chestnut.
Phytophthora
kernovii: In early 2004, some trees in Cornwall (UK) were
discovered to have a new disease - so new that the name has yet
to be scientifically formalised (at the time of writing). Phytophthora
are fungi - and usually harmless in their natural habitat. On the
other hand, it also from the same genus of organisms that led to
the potato blight (Phytphthora infestans) causing the famines.
The
first outbreak of the disease in the UK was discovered near Redruth
in Cornwall and was initially found to be infecting rhododendrons
and a beech tree. However, 30 beech trees and two pedunculate oaks
were subsequently found to be suffering from the disease as well,
which has caused real concern as it would be an uncomfortably close
relative of the dreaded Sudden Oak Death (seePhytophthora
ramorum, below) of America which has also found it's way
into this part of Britain. A 6-mile exclusion zone has been set
up in the area in the biggest excercise of it's type ever undertaken.
The photograph ( to the right) shows the disease
as it appears on a beech tree - source: Forestry
Commission, UK.
Rhododendenron would appear to be the main
carrier of the disease, and it succombs in just a few weeks.
It was initially hoped that native species,
such as oak, would be resistant to the disease, and some extensive
research in the UK appeared to prove this to be the case with Sudden
Oak Death. However, the infection of two peduncualte oak trees with
the new variation of the fungus is a worrying discovery.
Phytophthora
ramorum: Also known as Sudden Oak Death, the fungus has
caused widespread blight amongst American oak species. It was discovered
in Califronia in 1995. It was first found in Ireland in 2002.
The following text is from a Dail Debate
in June 2003 and a question put to the then Minister for Agriculture
& Food, Joe Walsh:
Tuesday, 10 June 2003
235. Mr. Deasy asked the Minister for
Agriculture and Food if plants can be imported without a phytosanitary
certificate; if his attention has been drawn to any cases here
of phytophthora ramorum (sudden oak death); the efforts being
made to ensure that this disease does not come here; and if he
will make a statement on the matter. [15260/03]
Minister for Agriculture and Food (Mr.
Walsh): Plants, planted or intended for planting, that arrive
in the European Union from third countries are required to be
covered by a plant health certificate issued by the plant protection
service of the country of export. Each consignment must be inspected
by the plant protection service of the member state of introduction
and found to conform to EU plant health requirements before it
can be released into free circulation in the EU.
Commission Decision 2002/757/EC of 19 September
2002 on provisional emergency phytosanitary measures to prevent
the introduction into and the spread within the Community of phytophthora
ramorum Werres, De Cock & Man in 't Veld sp. Nov., was agreed
in response to the threat posed by this new organism and its measures
became operative on 1 November 2002. Phytophthora ramorum has
been found in Ireland on a number of occasions. It has also been
found in at least nine other member states, including all of our
main trading partners. All infected plants that have been found
have been destroyed.
Host plants of the disease - plants
of rhododendron and viburnum species - within two meters of infected
plants have also been destroyed as required under EU legislation.
In addition, host plants within ten meters of infected plants
are required to be quarantined for three months. A survey for
the organism is being carried out in all member states. The survey
results are to be forwarded to the Commission by 1 November 2003
and the decision must be reviewed by 31 December this year at
the latest.
Pith: This is the
central core or heart of the tree. Pith wood can be quite soft,
and therefore prone to splitting when drying. It can have a deeper
colour than the wood around it.
Planer
thicknesser: A planer thicknesser is a machine that has two
functions, both based around the same blades (usually two or three
blades mounted on a spinning cylinder).
The first function is as a planer, where
timber is passed (on the top table) over the blades to give a
flat planed surface on one face of a board, or along the edge
of a board. Where planing the edge, a fence allows the timber
to be placed either at 90 degrees (i.e. square) to the blades
or at an angle to the blade. Usually up to 3mm can be removed
in a single pass over the planer.
The second function, as a thicknesser,
allows timber to be passed underneath the blades. The timber moves
over a table whose distance from the blades can be very precisely
adjusted by the operator. When a board is put into the thicknesser,
powered rollers grip the board and pass it under the blade at
a preset speed. The board is usually passed through the thicknesser
several times, with the table being raised slightly each time
(a mm or two at most usually) and that thickness being removed
from the thickness of the board until the exact desired thickness
is aquired.
Pocket: An
area where the timber has closed in around other material such
as bark or resin/pitch.
Pollarding:
A way of cutting trees so that they sprout upward growing branches.
The trees are cut at around eight feet in height.
Polyethylene Glycol
(PEG): A chemical which replaces the water within the pores
of the wood by a process of osmosis. It is frequently used by
wood workers to stabilise green wood. It also has the advantage
of acting as a lubricant by reducing friction in coarse open grained
wood. The wood is immersed in a PEG solution and allowed to soak.
Works better with planks, than with logs. PEG is sold in solid
and liquid forms.
Pores: These
are tiny holes (occurring in hardwood timber) which are at the
end of vessels running along the grain. They
are most prominent in the end grain (where
timber is cross cut), but also appear
obliquely in the sides and faces of timber.
Preservative:
Chemicals used to protect wood from decay. (We do not use preservatives
on our timber. Air drying is enough to kill fungi and kiln drying
will kill insects present.)
Propagation:
Regeneration of new plants by means other than seeds, e.g., rooting,
cuttings. (See also Natural Regeneration)
PTFE:
(Polytetrafluoroethylene). This is a chemically inert flouroplastic
polymer that is able to withstand high temperatures and which
causes little friction. It is probably best known for it's non-stick
uses in kitchen wares, where it usually takes the form of Teflon.
It is also well known to plumbers who use the tape for sealing
joints on pipes. However, PTFE also has it's uses in woodworking
machinery, such as planer thicknessers and saw tables or wherever
there is potential for friction between the machine and the wood.
PTFE (which is available in aerosol form) allows the wood to "glide"
over metal surfaces easily. It can also prevent machines clogging
up with wood shavings and sawdust, for example planer blades).
PTFE has relatively low flammability. It is quite expensive, but
a tin goes a long way and can make a very noticeable difference
to the smoothness of an operation.
Purlin: One
of a series of horizontal framing timbers supporting the rafters
or spanning between trusses or frames and supporting the roof.
Purlins usually span at right angles to the slope of the roof.
Q
Quarter-sawn
timber (edge grain): Timber
sawn so that the annual growth rings
are at an angle less than 45° to the face
of each board. The timber is stronger as a result, but the practice
is usually carried out to enhance the presence of medullary
rays, which are a very desirable feature
in oak furniture.
The
first picture (above right) shows the easier method of quarter
sawing. (Also shown in the photographs below) The log is quartered
into four sections. Each section is then propped at an angle and
sliced through-and-though.
The second picture (left) shows True Quarter
Sawing. As above, the log is sawn into four sections, or quarters.
But this time, instead of being sawn though-and-through, the section
is placed with one face square to the blade. The section is rotated
through 90 degrees for each saw cut.
Both methods are extremely time consuming
and laborious, but especially true quarter sawing, and as a result
quarter sawn timber is rare and expensive.
The log is sawn into four equal quarters
or sections. Because of the amount of time it takes to quarter
saw logs, the practice is reserved for the best logs only.
It is most commonly seen in oak.
On the saw bench, the sections are
placed at an angle to keep the growth rings virtually
at right angles to the saw blade. (The blade in the picture
is a horizontal one).
The boards are sawn from the top down,
and stacked as usual. This method of sawing results in
very narrow boards from the top & bottom of the section
being sawn, with the wider ones being from the middle
of the section.
R
Radial: A line
along the radius of a log. (i.e from the centre to the outside.)
Radially
Sawn: Radially sawn timber has been sawn along the radius,
producing a wedge or triangular shaped piece of wood. The cut
is at right angles to the growth rings.
Radial
Arm Saw: A saw used for cross-cutting pieces of timber at
very specific points and angles. The angles can be sawn with horizontal
and vertical variations. The saw blade slides back and forth to
allow wide cuts and non-vertical cuts. (N.B. The word "Radial"
refers to the saw itself, rather than the the way the timber is
cut)
Rays:
Bands of soft tissue vertically aligned and radiating from the
centre of the tree; insignificant in softwoods and variable in
hardwoods - if broad can produce distinctive figure - e.g. silver
grain in oak. (See Medullary Rays)
Relative
humidity (RH): The ratio of the amount of water vapour present
in air to the amount which the air would hold if saturated at
the same temperature.
Regeneration:
The production of new trees by natural seeding. (See also Natural
Regeneration)
Ring shake:
Where the timber splits around a growth ring - also known as cup
shake.
Rip: To saw timber
along the grain.
Ripple: A wavy
or ripple effect on the grain, typically in sycamore and maple
and often used for the backs of violins - also known as fiddleback.
Rot:
Decay or decomposition of wood, initiated by fungi. See decay
or fungi.
Rough Sawn:
A description of timber that has been sawn in a sawmill. It has
not yet been sawn accurately, nor planed. The width (especially)
of rough sawn boards may vary, particularly after drying/seasoning.
Router:
A machine used to gouge out timber. For example it may be used
along the edge of an otherwise finished piece of wood to produce
a bevelled edge, or it can be used for occasional morticing work.
S
Sapwood:
This is the wood from the outer growth rings, extending from the
heartwood to the cambium. Sapwood contains living cells, with
carbohydrate food reserves, and conducts the sap up the tree.
It is generally lighter in colour and wetter than heartwood
when freshly felled, and is generally more perishable.
Sealing: A
sealer is applied to wood to stop water or other materials from
getting into the timber and staining it or increasing moisture
levels.
Seasoning
or drying: The process
of removing moisture from timber. Seasoning often refers to drying
in the atmosphere (air drying), or kiln
drying by accelerated drying under controlled conditions in
a kiln.
(Also see the "Practices"
section of our website, which gives more information on all of
the processes involved in producing timber).
Shake: A separation
or splitting of the fibres along the grain, usually between the
annual rings (see Cup shake/Ring Shake),
or radially (see Star Shake)
Shrinkage:
The reduction in size of a piece of timber as a result of the
removal of water. A 12" wide board might shrink by perhaps
1/2" during the drying process. The amount of shrinkage depends
on the moisture levels before and after drying, density of the
material, etc.
Softwood:
This is timber from (usually) conifer trees.
The term relates to the botanical grouping of the trees and not
to the hardness of the wood ( some softwoods, e.g. yew, are harder
than some hardwoods).
Spalting:
Spalted wood is sought after because of the patterns, colours
and appearance. The spalting is caused by fungal decay, representing
the early stages of the entirely natural process of "rotting"
that occurs in timber. Whilst spalted wood can have soft areas,
the ideal piece of spalted wood has been dried just before the
wood has started to soften too much and the patterns caused by
the fungal decay are at their peak. (Fungal decay stops when timber
reaches 20% MC or less.) Spalting occurs in most hardwood timbers,
but is most commonly found in beech.
Species:
This is a biological classification, below "genus".
Organisms that can interbreed with each other and produce fertile
offspring are (usually, but not always) of the same species.
Spiral grain:
Growth of fibres in a spiral direction around the trunk of the
tree. It may cause twisting of timber during drying.
Split:
If a log of timber has tension, or stress
in it (which can occur for multiple reasons), then sawmilling
or drying the timber can bring that stress to the point where
the fibres in the wood pull apart to release the tension, and
thereby cause a split (also known as shake). Drying timber can
exaggerate the stresses and sawing or planing the timber can reduce
the strength of the wood to resist splitting, so timber can split
during any of these processes. Small shallow cracks on the surface
are called checking, and occur during
drying timber. Shallow check is generally not a problem as they
are machined out during planing.
Spring: A curve
along the edge of a plank; normally due to growth stress.
Square
edged: A description of a board that has been sawn with both
sides cut square (i.e. the bark/wane has been
removed). Because of the way that timber moves during drying,
the square edges can distort. The phrase refers to the way the
timber has been cut, rather than how it will appear after drying.
Square edged timber needs to be resawn or trimmed after drying
to get a truly square edge.
Star Shake:
Where cracks radiate from the pith to the outside of the tree.
Straight grained:
Where the grain (fibres) of the piece run almost perfectly parallel
to the pith with little distortion.
Streaks: (e.g.
mineral) Staining of the wood from the take-up of minerals in
the ground surrounding the tree.
Stress:
The applied force per unit area or volume. The primary stresses
are tensile, compression and shear. A combination of all three
occurs in bending.
Stickers:
Length of wood used to aid the drying process. Stickers are placed
at regular intervals across a board of wood. Another board is
then placed on top of the stickers, this is continued to form
a stack of boards. The stickers are very important as they allow
air to circulate between the boards, thereby helping the boards
to dry evenly. It is important to use the correct size of sticker.
For difficult woods like oak the stickers should not be thicker
than 13mm. For woods such as pine, beech, etc. they should be
25mm, for 25mm boards. For thicker boards the stickers should
be 13mm (6mm for thick oak).
(Also see the "Practices"
section of our website, which gives more information on all of
the processes involved in producing timber).
Structural
timber: Timber used for specific tasks in construction where
it needs to be of a minimum strength.
Tension wood:
This occurs in hardwood trees that are leaning against other trees.
The upper side of the trunk becomes compressed, and as a result
the timber from this part of the trunk is prone to distortion.
Through-and-through:
(Also known as T&T or T/T) Where a log is sawn from top to
bottom without being squared off, so that the bark (or wane) is
showing along both sides of the board. This is a quick way to
saw a log, but if the bark or wane is not wanted for the final
end-use of the timber, then valuable storage space and and drying
costs are being applied to what is (effectively) waste material.
(Also see the "What
We Do" section of our website, which gives more information
on all of the processes involved in producing timber).
Through Check:
This is where a crack/split runs right through a board from one
face to the other.
Tie: To 'tie'
is a method of securing thin or short grain parts of a carving.
This is done by linking one part of a carving to another in such
a way that it strengthens the thin bit while not being obvious.
For example, you could link the stems of flowers by having them
criss cross each other thereby providing great support for both
stems, or having fragile leaves lie on top of one another, again
adding support. As both these happen in nature, you would provide
support whilst keeping within the context of the piece.
Timber: A term
to describe wood in the form of (for example) trees, logs, boards
or beams.
Tongue
and groove (T&G): A method of joining two boards side
by side. One board has a groove cut, or routed, along the edge
to be joined. The other board has a tongue(formed by creating
two rebates either side of it) along the matching edge. The two
boards are then slotted together. They can be glued in place,
or left free to move (to allow for expansion/contraction of the
wood). T&G boards are used for flooring where they are free
to move at the same time as forming a dust proof barrier.
Twist: This
is where one corner of a board moves out of the general plane
of the rest of the board. See warp.
U
Unseasoned
Timber: Timber that has not been dried (seasoned), and typically
with a moisture content exceeding 25%.
V
Veneer: A very
thin slice of wood. It is usually applied to another material
(chipboard, composite material, softwood, etc.) in order to give
the appearance of being a solid piece of wood of the veneer's
species.
W
Wane:
The original rounded surface of a tree that remains (with or without
bark) on a board after sawmilling.
Waney
Edged: A description of a board where (usually) one side of
a board is sawn square , and the other side is not sawn at all,
thus retaining the edge of the tree, or wane.
This type of board might be used, for example, by a furniture
maker who wants to give a rustic and uneven appearance to furniture
along an edge.
(Also see the "What
We Do" section of our website, which gives more information
on all of the processes involved in producing timber).
Warp: A twist
in a board resulting from movement of the timber caused by the
release of tension and stresses in the wood fibres. These stresses
can be released by sawmilling, drying or planing the wood. With
the stresses released, the wood fibres "relax" and can
cause considerable movement in a piece of timber.
The material which is produced by a
tree, and of which that tree substantially comprises. Wood is
made up of fibres (small vessels) through which nutrients are
supplied to the growing parts of the tree by capillary action.
The active fibres are in the sapwood. See also Sapwood,
Heartwood, Cambium
and Pith.
An area of ground in which several trees
are growing - i.e. Woodland, forest.
Workability:
The ease with which wood can be worked.
Page Updated:
Friday, 14 December, 2007
The
first outbreak of the disease in the UK was discovered near Redruth
in Cornwall and was initially found to be infecting rhododendrons
and a beech tree. However, 30 beech trees and two pedunculate oaks
were subsequently found to be suffering from the disease as well,
which has caused real concern as it would be an uncomfortably close
relative of the dreaded Sudden Oak Death (see 
The
first picture (above right) shows the easier method of quarter
sawing. (Also shown in the photographs below) The log is quartered
into four sections. Each section is then propped at an angle and
sliced through-and-though.
