Understanding Veneer Thickness in Plywood Production

Veneer thickness is a critical factor in high-quality plywood production, yet it's often misunderstood. The final strength, stability, and aesthetics of plywood are all dependent on how this measurement is managed throughout the manufacturing process. This guide provides a comprehensive overview of veneer thickness, from the initial cut to the final product, helping manufacturers and enthusiasts produce superior plywood.

The Four Types of Veneer Thickness

Veneer thickness changes significantly throughout production. To manage it effectively, manufacturers track four key measurements:

• Nominal Thickness: The theoretical thickness of a single veneer, calculated by dividing the total finished plywood thickness by the number of layers.

• Actual Peeling Thickness: The measurement right after slicing the log. This is intentionally thicker than the nominal value to account for changes during subsequent steps.

• Thickness After Drying: The measurement taken after the veneer's moisture content is reduced. This value is smaller than the peeling thickness due to shrinkage.

• Final Plywood Thickness: The compressed thickness of the veneer once it's been glued and hot-pressed into a finished panel.

To ensure precision, a screw micrometer is used to measure the veneer at a consistent point during each stage of the process, tracking even the smallest changes.

How Veneer Thickness Changes During Production

The thickness of a veneer is not static; it's a dynamic variable influenced by several forces in the manufacturing process:

• Rebound: After being compressed by the peeling machine's pressure bar, the veneer's elastic properties cause it to expand slightly.

• Drying Shrinkage: The process of drying a veneer to its target moisture content causes it to shrink, resulting in a noticeable reduction in thickness. This rate varies based on wood species and drying conditions.

• Expansion: The moisture from the adhesive applied during the gluing process causes the veneer to absorb water and swell slightly before being pressed.

• Compression: The most significant change occurs during hot pressing, where heat and high pressure compact the veneers, permanently reducing their thickness to form the final plywood panel.

Calculating Peeling Thickness from Finished Plywood

To produce a plywood panel of a specific thickness (e.g., 18mm), a manufacturer must reverse-engineer the initial peeling thickness. The formula must account for all the changes the veneer will undergo.

Peeling Thickness = (Finished Plywood Thickness / Number of Layers) + Process Allowance - Rebound - Expansion

• Process Allowance: An added margin to offset shrinkage, compression, and other variables.

• Rebound & Expansion: These factors, which increase thickness, are subtracted from the calculation to arrive at the correct initial cut.

For a more precise calculation, use factory-specific data for shrinkage and compression values, as these can vary significantly from general theoretical values.

For example, to produce a five-layer, 18mm plywood, if the process allowance is 0.2mm, rebound is 0.05mm, and expansion is 0.1mm, the required peeling thickness would be: