Transcript Conversion of Timber - Industrial Techniques grade 8

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CONVERSION
Conversion of Timber
Grade 8
The Conversion of timber process
video clip of the conversion
process
What is conversion of timber
• The process of cutting logs into timber is
called conversion.
• There are several methods of conversion,
each of which has some special
advantage. For some timbers conversion
must take place before the log has time to
dry out and shrink.
What are some of the factors that
determine the type of cut?
The way the cuts are made will depend on
several factors ,some of which are:
• The type of sawing machine
• The condition of the log
• Economy
• The size of log
• The wood species
• The end use of resulting timber
What are the types of sawn
Lumber?
Methods of conversion of timber
There are three main methods of conversion
of timber. They are :
• Plain sawn
• Quarter sawn
• Rift sawn
Plain sawn
• Plain sawn which is sometimes called
through-and-through or slash sawing. In
plain sawing, the saw cut forms a tangent
to one of the annual rings. There are
several variations of plain sawing
Picture of plain sawn
Plain Sawn
Advantages of plain sawn
• The log is easily-manipulated and frequent
turning is not required.
• There is no waste of timber.
• It is a cheaper method
Disadvantage of plain sawn
• It has the disadvantage that shrinkage may tend
to warp and split the boards.
• They also tend to absorb more moisture from the
air which can also lead to unwanted movement
Quarter Sawn
• Quarter sawn lumber comes at a premium
due to the labor it takes to mill each plank.
To mill quarter sawn wood, each log is
sawed at a radial angle into four quarters.
Then each quarter is plain sawn. This
method of quarter sawing does leave
some waste, but much less than rift sawn
lumber.
Quarter sawn
• In quarter sawing , the saw cut is made at
right angles to the annual rings. This
method is used particularly to produce
figured oak. A quarter sawn board will
therefore expose the rays where as a plain
sawn one would cut across them.
Picture of Quarter sawn
Quarter sawn
Advantages of Quarter Sawn
• Smoother surface due to less distinct grain
• Decreased expansion and contraction on the plank’s
width
• Twisting, cupping, and warping resistance
• Ages evenly over time
• Chances of surface checking are significantly reduced
• More resistant to moisture penetration
• Enhanced paint retention
Quarter sawn
Disadvantage of Quarter Sawn
• The cutting operation is much more
complicated and involves more waste.
• The boards are rather narrow.
• It is an expensive method
Rift sawn
• Milling rift sawn lumber takes more time
and labor. It also has unique benefits over
quarter and plain sawn lumber. Furniture
makers depend on this cut of wood for the
vertical grain that is shown from all sides.
This linear grain pattern is achieved by
milled perpendicular to log's growth rings.
The log is milled carefully on an angle
between 45° to 75°.
Rift sawn
Rift sawn
Advantages of Rift Sawn
• Ideal for custom furniture makers to use for
table, chair and other straight pieces
• The most dimensionally stable cut of lumber
available
• Unique, linear appearance on both sides of the
lumber planks
• Rift sawn lumber is dimensionally superior to
both plain sawn and quarter sawn lumber.
Rift Sawn
Disadvantage of Rift Sawn
• they also produce the most waste.
• rift sawn lumber will cost more per board
foot than either quarter sawn and plain
sawn lumber.
Plain and Quarter
Sawn lumber
Plain Sawn
•Faster to produce
•More affordable
•Displays varied grain patterns & the
unique "cathedral" appearance
•Readily available
vs
Quarter Sawn
•More stable than plain sawn lumber
•Increased moisture resistance
•Less likely to cup, twist & warp
•Beautiful ribbon aka "fleck" patterns are
prevalent in species like White Oak & Red
Oak
•Less expensive than rift sawn lumber
vs
Rift Sawn
•Ideal for custom furniture makers to use
for table, chair and other straight pieces
•The most dimensionally stable cut of
lumber available
•Unique, linear appearance on both sides
of the lumber planks
Plain sawn Vs Quarter sawn
Why is it important to have allowance cut the
logs into timber?
• When sawing, an allowance is made for
shrinkage and for planing the boards to
the required finished sizes.
summary
classwork
• Write a letter to their best friend telling him
or her how logs are converted into timber .