chapter 2 lumber. manufacture of lumber logs arrive at a sawmill and the bark is removed. a bandsaw...

Chapter 2

Lumber

Manufacture of Lumber

• Logs arrive at a sawmill and the bark is removed.

• A bandsaw cuts the log into planks.• A series of saws are used to slice, edge

and trim.• The wood is cut to various dimensions.• Wood is stacked with stickers to dry.

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Manufacture of Lumber (cont.)

• Lumber is standardized and shipped.

• Measuring termsEdge – long, narrow surface of board

Side – long, wide surface of board

Ends – the cross sectional extremes of board

Thickness – narrow distance across the end

Width – distance across the side

Length – distance from end to end

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Plain-Sawed Lumber

• Common way of cutting lumber.• Log is cut tangent to annular rings.• This produces a distinctive grain.• Least expensive, producing greater widths.• Shrinks and swells unevenly, tends to warp.• Sometimes called slash-sawed.

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Plain Sawn

Quarter-Sawed Lumber

• Produces pieces with annular rings at right angles.

• Shrinks evenly, warps less easily.• High durability.• Frequently used for flooring.• Also called vertical-grain or edge-grain.

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Quarter Sawn

Combination Sawing

• Process of varying the cutting styles to produce a mixture of plain and quarter sawn lumber.

• More efficient use of materials.

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Moisture Content and Shrinkage

• Green Lumber– Water fills the wood cell tubes.– Newly cut wood that hasn’t dried and will

shrink.– As it shrinks, it usually changes shape.– Subject to decay due to its moisture content.

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Moisture Content and Shrinkage

• Seasoned Lumber – Lumber that has been dried.– Should be protected from moisture.

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Moisture Content (MC)• Expressed as a percentage.• Determined by the weight of water

removed by oven drying and dividing that number by the dry weight.• Example – if a wood sample is 16 ounces

wet and 13 ounces dry, then

%2310013

1316

MC

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Drying Lumber

• Lumber is air dried by stacking in piles with stickers between layers.

• Later it is moved into huge ovens called kilns that provide controlled temperatures, humidity and air circulation.

• Kiln drying speeds up the drying time but is more costly.

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Drying Lumber (cont.)

• Recommended MC • Framing lumber less than 19%• Exterior finish lumber – 12%• Interior trim and cabinet work – 8-10%

• Moisture meters are used to measure moisture content.

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Lumber Storage

• Store lumber so it is protected from moisture and other hazards.

• Keep lumber off the ground.• Cover with a tarp, leaving room for air

circulation.

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Lumber Defects• A defect is any fault that detracts from its

appearance and strength.

• Warps are caused by drying lumber too fast, poor storage, or surfacing lumber before it is dry.

• Splits and checks are caused by uneven drying.

• Shakes run parallel to annular rings.

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Lumber Defects (cont.)

• Lumber with high percentage of juvenile wood tends to warp and twist more.

• Knots are cross-sections of branches in the trunk of the tree.

• Pitch pockets are small cavities holding pitch.

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Lumber Defects (cont.)

• Wane is bark on the edge of lumber.• Pecky wood has small grooves through

the grain.

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Board defect types

Lumber Grades and Sizes

• Largest manufacturer of softwood is Western Wood Products Association (WWPA).

• Hardwood grades established by the National Hardwood Lumber Association.

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Softwood Lumber Grades

• Three general categories– Boards – 1 inch or less in

thickness i.e. 1x6

– Dimension Lumber – 2 inches in thickness i.e. 2x6

– Timbers – larger than 2 inches in thickness i.e. 4x6

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1x6

2x6

4x6

Hardwood Lumber Grades

• Firsts and seconds (FAS) is the best grade.

• Each piece must be at least 6” wide by 8’ long.

• Next best grade is called Select.• No. 1 common grade allows narrower

widths and shorter lengths.

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Lumber Sizes

• Rough lumber that comes directly from the sawmill is close to nominal size.

• Planing reduces the thickness and width to standard and uniform sizes.

• Nominal size – what the piece is called• Actual size – the actual measurements

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Lumber Sizes (cont.)

• Lumber sizes are indicated by a series of numbers.

• Thickness” × Width” × Length’– For example, 1” × 10” – 12’

– One inch thick × 10 inches wide and 12 feet long

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Actual vs. Nominal

• Actual dimensions of lumber are smaller than the name implies.

• For example: – Nominal 2 x 6

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6″

2″ `2x6

Actual vs. Nominal

– Actual

1½” x 5½”

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5½”

1½″

`2x6

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Board Foot Measure

• Lumber may be purchased by the piece.– i.e. 36 – 2x8 –16′

• Large quantities of lumber are often purchased by the board foot (bdft).– i.e. 750 bdft of 2x4’s– This is typically done at the wholesale level.– Also allows purchasing of varying board sizes.

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Board Foot Measure (cont.)• Board foot measure refers to a volume of

wood.

• It is defined as the volume of wood measuring 1” × 12” × 1’

• One board foot may have many shapes.

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1″12″

1 foot

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BDFT Calculations (cont.)

Formula for figuring board feet is:

Bdft = # pieces × Thickness″ × Width″ × Length′ ÷ 12

Note: Thickness (inches), Width (inches), & Length (feet)

Example – How many board feet are in 180 pieces of 2x816′ long?

180 × 2 × 8 × 16 ÷ 12 = 3840 bdft

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Conclusion

• Lumber is plain sawn or quarter sawn.

• Moisture content of wood is important.

• Wood can be air dried or kiln dried.

• Defects affect appearance and strength.

• There are many different grades of wood.

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Conclusion (cont.)

• Nominal size is not the same as actual.

• Board foot is a measure of wood volume.

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