Select and Prepare Materials

Choosing and Preparing Materials

This chapter covers the knowledge required for the Red Seal exam in cabinetmaking regarding the selection, evaluation, and preparation of materials. You will find the technical principles, calculations, applicable Canadian standards, and common pitfalls to avoid.

1. Classification and Properties of Wood

1.1 Softwoods vs. Hardwoods

Material selection begins with understanding the two major botanical families.

Rule of thumb: for a drawer or visible panel, choose a hardwood. For a non-visible carcass, a stable softwood (pine, fir) is sufficient.

1.2 Common Hardwoods in Cabinetmaking

1.3 Moisture Content and Equilibrium Moisture Content

Moisture content (MC) is the ratio of the mass of water in the wood to its oven-dry mass. It is calculated as:

MC (%) = (Wet mass – Oven-dry mass) / Oven-dry mass × 100

Example: a board weighs 2.5 kg at purchase and 2.1 kg after oven-drying.

MC = (2.5 – 2.1) / 2.1 × 100 = 19.0%

Equilibrium moisture content (EMC) depends on the temperature and relative humidity of the air. In Canada, for a heated interior (20 °C, 35-45% RH), the EMC is 6 to 8%. For an unheated garage, it can reach 12-14%.

Exam rule: wood must be acclimatized to the humidity of the final use location before machining. A 2% difference between two assembled pieces will cause warping or cracking.

1.4 Shrinkage and Swelling

Shrinkage is anisotropic: it is greatest in the tangential direction (6-10%), half that in the radial direction (3-5%), and almost negligible in the longitudinal direction (0.1-0.3%).

Calculating expected shrinkage:

ΔL = L × (MC₁ – MC₂) × S

Where:

Example: an oak board 200 mm wide (tangential direction, S = 0.35%/% MC) goes from 12% to 7% MC.

ΔL = 200 × (12 – 7) × 0.0035 = 3.5 mm

This board will shrink 3.5 mm in width. Trap: do not confuse S as a fraction (0.0035) versus S as a percentage (0.35%). Always use the fraction in the calculation.

2. Canadian Standards and Wood Grading

2.1 Grading and Drying Standards

The National Lumber Grades Authority (NLGA) publishes the grading rules for framing and millwork lumber in Canada. The main grades for cabinetmaking:

For hardwoods, grading follows the NHLA (National Hardwood Lumber Association): FAS (First and Second), Select, No. 1 Common, No. 2 Common. In cabinetmaking, FAS or Select is generally required for visible faces.

2.2 Plywood and Composite Panels

Exam rule: CSA O121 birch plywood is the standard for quality drawer boxes. MDF is preferred for painted doors because it has no grain and will not warp.

2.3 Veneers and Veneered Panels

A veneer has a thickness of 0.5 to 3 mm. Veneered panels consist of a core (MDF, particleboard, or laminated) covered with a hardwood veneer. CSA O153 covers veneered panels for interior use.

Trap: a 0.6 mm veneer cannot be sanded more than 0.2 mm total. Excessive sanding will cut through the veneer and expose the core.

3. Material Selection by Application

3.1 Selection Criteria

For each piece of furniture, evaluate:

3.2 Quick Selection Table

3.3 Deflection Calculation for Shelves

The maximum allowable deflection for a shelf is L/360 (L = span in mm). For a span of 900 mm, the maximum deflection = 900/360 = 2.5 mm.

Deflection formula for a uniformly distributed load (simple supports):

δ = (5 × q × L⁴) / (384 × E × I)

Where:

Example: birch shelf (E = 10,000 N/mm²), width b = 300 mm, thickness h = 19 mm, span L = 800 mm, load q = 0.005 N/mm (≈ 5 kg/m).

I = (300 × 19³) / 12 = (300 × 6,859) / 12 = 171,475 mm⁴

δ = (5 × 0.005 × 800⁴) / (384 × 10,000 × 171,475)

δ = (5 × 0.005 × 4.096 × 10¹¹) / (6.585 × 10¹¹)

δ = 1.024 × 10¹⁰ / 6.585 × 10¹¹ = 0.0155 mm

The deflection is negligible. Trap: if the thickness doubles, the deflection is divided by 8 (h³). Always check the thickness before calculating.

4. Material Preparation

4.1 Cutting and Selecting Pieces

Cutting involves sawing boards into blanks while considering:

3 mm rule: any piece intended for a visible surface must be cut with at least 3 mm of surplus per machined face.

4.2 Surfacing and Thicknessing

Surfacing (jointing) creates a flat face perpendicular to the adjacent edge. Thicknessing (planing) brings the thickness to the final dimension.

Correct procedure:

Frequent error: thicknessing before surfacing. The piece has no flat reference face, and the thickness will be uneven.

4.3 Gluing and Pressing

Wood gluing requires:

Reference standard: CSA O112 covers glues and adhesives for wood. Yellow glue (Type II) resists moderate humidity; white glue (Type I) is for dry interior use only.

4.4 Sanding

Standard sanding sequence for a lacquered finish:

Rule: never skip more than one grit (e.g., going from 80 to 180 is not allowed). Each subsequent grit must remove the scratches from the previous one.

5. Safety and Environmental Standards

5.1 Wood Dust

Wood dust is classified as a known carcinogen (Group 1) by the IARC. The most dangerous species: oak, beech, birch. The Canada Labour Code (Canada Occupational Health and Safety Regulations) sets the exposure limit for wood dust at 1 mg/m³ (inhalable fraction) for hardwoods and 5 mg/m³ for softwoods.

Required equipment: source extraction (dust collector with HEPA filter), N95 mask minimum, safety glasses.

5.2 Finishes and VOCs

Finishes containing volatile organic compounds (VOCs) are governed by the Consumer Products Containing Lead Regulations (Health Canada) and ventilation standards. Use low-VOC products (< 250 g/L for lacquers) and ensure ventilation of 10 air changes per hour in a spray booth.

5.3 Legal Sourcing

Wood must come from legal sources. The Canada Wildlife Act and the CITES Convention regulate the importation of exotic woods (rosewood, ebony). Require a certificate of origin for any imported wood.

6. Quality Control and Inspection

6.1 Receiving Inspection

Upon delivery, check:

6.2 Machining Tolerances

Trap: tolerances add up. If you stack 3 operations at ± 0.5 mm, the total deviation can reach ± 1.5 mm, which is visible on a joint.

7. Quantity and Cost Calculations

7.1 Calculating Veneer Surface Area

To veneer a panel 600 mm × 900 mm with a 0.6 mm veneer:

Surface area = 0.6 × 0.9 = 0.54 m²

Add 10% for waste (cutting, matching): 0.54 × 1.1 = 0.594 m² of veneer required.

7.2 Calculating Solid Wood Volume

A board 2.4 m × 150 mm × 50 mm:

Volume = 2.4 × 0.15 × 0.05 = 0.018 m³

At a price of $1,200/m³, the cost = 0.018 × 1,200 = $21.60

7.3 Cutting Yield

The typical yield of a hardwood board is 60 to 70% (the rest is lost to offcuts, defects, over-thickness). For an order of 10 m² of finished surface, plan for:

Gross surface = 10 / 0.65 = 15.4 m² of wood to purchase.

8. Summary

9. Pitfalls to Avoid

This chapter covers the essentials for passing the "Material Selection and Preparation" section of the Red Seal exam. Review the shrinkage and deflection calculations, memorize the CSA standards, and practice identifying wood defects on real samples. Good luck with your preparation.