Sawmill Operation

Report
FW1035
Lecture 13
Bowyer et al, Chapter 13
Lumber Grades
Grading is typically by:
1. Strength
1. Visual Estimation
2. Measured
2. Appearance
3. Specialty product needs
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Hardwood Lumber Grading
Factory Lumber
Lengths from 4 to 16 feet in one foot increments, random widths.
Graded according to the size and number of small clear “cuttings”
that can be cut from board.
Dimension and Component Parts
Small board or part machined to a size for a particular application.
Finished as specified by customer. May be partially or completely
machined to final shape
Finished Market Commodity Products
E.g. strip flooring, railway ties, stair threads, etc.
Typically graded according to relevant trade association rules.
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Hardwood Factory Lumber Grading
• Hardwood lumber grading scheme is set by
the NHLA (National Hardwood Lumber
Association).
• Factory lumber is typically sold by sawmill to
a furniture or cabinet manufacturing plant
• Grade is proportional to board size and the
amount of clear surface area
• a higher grade board is long and wide, with a large
percentage of its area being defect-free
• the clear lumber can be removed in a few relatively large
cuttings
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Furniture is typically an assembly
of small pieces of wood, hence
the grading rules for hardwoods.
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Hardwood grades are determined on poorer side of board,
except for FIF and Selects.
NHLA – National Hardwood Lumber Association
FAS – Firsts and Seconds
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FIF – FAS on one face
Example of Specialty Market Product Grading
Maple Flooring Manufacturers Association
First Grade – one face practically free of all imperfections;
variations in natural color of wood allowed.
Second Grade – tight, sound knots (except on edges or
ends) and other slight imperfections allowed; must be
possible to lay flooring without waste.
Third Grade – may contain all visual features common to
maple; will not admit voids on edges or ends, or holes over
3/8 inch in diameter; must permit proper laying of floor and
provide a serviceable floor.
Fourth Grade – may contain all visual features, but must be
possible to lay a serviceable floor, with some cutting.
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Examples of Maple Flooring Grades
First Grade
Second Grade
Third Grade
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Softwoods – Graded in Two Major
Categories
1. Construction
•
•
•
Intended for use as it comes from lumber mill
Strength properties are most important
Two subcategories
•
•
Visually graded Lumber
Machine graded lumber
2. Appearance
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•
•
•
•
Intended for remanufacture
Grade is based on appearance
Also called “shop lumber”
Uses: pencil stock, ladder parts, boxes, mouldings, siding,
flooring
Also includes specialty species lumber products – e.g. redwood
Softwood lumber in the United States is most commonly graded
according to the guidelines of the American Softwood Lumber Standard
PS 20-70, established by the U. S. Department of Commerce.
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Visually Graded Construction Lumber
Defects are allowed to become larger and more frequent
as the grade drops. Commonly considered defects:
1. Location, size and placement of knots
2. Slope of grain
3. manufacturing defects (splits from drying
4. Wane
5. Warp
It is assumed that as the defects become larger and more
frequent, strength properties drop.
Lengths in 2 foot increments (6 to 18 feet)
Common widths – 2, 3, 4, 6, 8, 10, and 12 inches nominal
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National Softwood Construction Lumber Grades
Lumber Class
(Nominal Dimensions)
Grade Name
Bending
Strength (%)
Light Framing
(2 to 4 inches thick, 4 inches wide)
Construction
Standard
Utility
34
19
9
Structural Light Framing
(2 to 4 inches thick, 2 to 4 inches wide)
Select Structural
1
2
3
67
55
45
26
Studs
(2 to 4 inches thick, 2 to 4 inches wide)
Stud
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Structural Joists and Planks
(2 to 4 inches thick, 6 inches and wider)
Select Structural
1
2
3
65
55
45
26
Appearance Framing
(2 to 4 inches thick, 2 to 4 inches wide)
Appearance
55
“Bending Strength” is percentage of properties of clear (defect-free) wood.
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Common Visual Lumber Grades
No. 1 - Moderate-sized tight knots. Paints well. Used for siding,
cornice, shelving, paneling, some furniture.
No. 2 - Knots larger and more numerous. Paints fair. Similar uses as
No. 1.
No. 3 - Splits and knotholes present. Does not take paint well. Used
for crates, pallets, sheathing, subflooring, small furniture parts.
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No. 1
No. 2
No. 3
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Appearance Softwood Lumber Grades
Two primary grades – “Finish” and “Select”
- Finish grades are higher than Select grades
- Subgrades are usually letters – A, B, C, D
To simplify grading at the mill, grades are often
combined.
- E.g. A and B combined to “B&BTR”
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Appearance Lumber “Select” Grades
A Select - No knots, splits, or other visible defects. Used for
fine furniture, exposed cabinetry, trim, flooring
B Select - A few, small defects but nearly perfect. Used for
fine furniture, exposed cabinetry, trim, flooring.
C Select - Small tight knots. May be nearly perfect on one
side. Used for most furniture, shelving, some trim and
flooring.
D Select - More numerous "pin" knots and other small
blemishes. May be used for some furniture, shelving, some
trim and flooring.
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Moisture Content Marking on Grade
Stamp
S-GRN – Surfaced in green condition.
S-Dry – Surfaced dry. MC is less than 19% after manufacture.
MC15/KD15 – MC was less than 15% at time of manufacture.
KDHT – Kiln-dried and heat-treated. Dried to <19% MC with core
brought to 56° C for 30 minutes. HT kills insects and decay fungi
spores. Done to meet global shipping requirements.
The stamp only shows the MC of the lumber at time of manufacture.
Subsequent history (rain, sitting in mud or puddles) may have raised
the MC.
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Softwood Grading Certification
Agencies
RIS – Redwood Inspection Agency. Grades redwood lumber only.
NELMA – Northeastern Lumber Manufacturers Association. New
England and the Middle Atlantic states.
NHPMA – Northern Hardwood and Pine Manufacturers Association.
Lake States.
SPIB – Southern Pine Inspection Bureau. Grades southern pine lumber
only.
WCLB – West Coast Lumber Inspection Bureau. Pacific coast states.
WWPA – Western Wood Products Association. Thirteen western states.
There is a similar set-up in Canada with similar grades.
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Example of Softwood Specialty Grading
California Redwood Association, “Architectural Grades”
Clear All Heart Free of defects one
face, reverse face may have slight
imperfections. Uses - Siding,
paneling, trim, cabinetry, molding,
fascia, soffits, millwork. Also fine
decks, hot tubs, garden structures,
industrial storage and processing
tanks.
Heart B Heartwood grade
containing limited knots and
other characteristics not
permitted in Clear All Heart and
Heart Clear. Uses - Siding,
paneling, trim, fascia, molding
and other architectural uses.
Quality decking, garden shelters
and other outdoor uses in contact
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with the ground.
Clear Same general quality as
Clear All Heart except contains
sapwood in varying amounts.
Uses - Siding, paneling, trim,
cabinetry, molding, fascia, soffits.
Also quality decking, garden
shelters and other above-ground
applications.
B Grade Grade containing
sapwood, limited knots and other
characteristics not permitted in
Clear. Uses - Siding, paneling,
trim, fascia, molding and other
architectural uses; quality
decking, garden shelters and
other above-ground outdoor
applications.
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Machine Graded Lumber
MSR – Machine Stress Rated
- Based on measured MOE in bending
MEL – Machine Evaluated Lumber
- Based on estimated density (using x-rays)
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Grade Stamp
OLMA – Ontario Lumber Manufacturers Association
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