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【Artificial Board Processing 】 Series Ⅲ-Rotary Veneer Knife Geometry Explained
Jan 28,2026
In rotary veneer production, knife geometry plays a key role in veneer quality, thickness stability, cutting load, and machine running smoothness. To help operators and new technicians better understand setup and adjustment, Hummingbird Machinery has compiled a clear explanation of the main rotary peeling knife angles: Grinding Angle (β), Clearance Angle (α), Cutting Angle (δ), Complement Angle (ε), and Setting Angle (θ), including the original calculation formula.
1. Grinding Angle β (Grinding Angle / Bevel Angle)
Grinding Angle (β) is the angle between the front knife face (the surface the veneer flows along) and the rear knife face (the surface facing the log).
How β is selected
The β value is typically determined by:
knife material type
peeled veneer thickness
wood species
wood temperature and moisture content
Common range in production
β is generally 18°–23°.
To obtain higher-quality veneer, reduce β as much as practical when conditions allow.
When other conditions remain the same, hardwood, thicker veneer, and knotty logs usually require a larger β.
2. Clearance Angle α and Cutting Angle δ
Definitions
Clearance Angle (α): the angle between the rear knife face and the tangent line of the peeling curve at the cutting edge.
Cutting Angle (δ): the angle between the tangent line and the front knife face.
Relationship:
δ = β + α
In practice, clearance angle reflects the contact area between the rear knife face and the log surface, which indicates the level of support force provided by the log.
To maintain stable peeling, the contact width between the rear knife face and the log surface is commonly kept within:
Hardwood: ~2–3 mm
Softwood: ~2–4 mm
When α is too large
Veneer tends to bend backward more easily and may crack
The knife holder can become prone to vibration, and veneer may turn wavy/corrugated
When α is too small
Knife pressure on the log increases, which may cause log splitting or bending
Veneer thickness may vary during peeling
Reference values during peeling
For large log diameter: α can be 3°–4°
For small diameter: α can be 1°, and in some cases even negative, depending on wood species and veneer thickness.
During peeling, the log diameter decreases continuously. In many setups, α should reduce as diameter becomes smaller, and the practical variation range is often controlled around 1°–3°.
3. Complement Angle ε and Setting Angle θ (Installation Geometry)
Complement Angle (ε): the angle between the tangent line and the vertical line. When determining clearance angle, it is necessary to know ε.
Setting Angle (θ): the angle between the rear knife face and the vertical line.
Relationship:
θ = α + ε
Where:
a — base circle radius of the Archimedean spiral segmentation circle
s — peeled veneer thickness
h — vertical distance from the knife edge to the horizontal plane of the spindle axis
r — instantaneous log radius during peeling
Practical Notes from Hummingbird Machinery
For field setup and daily adjustment, operators usually follow this logic:
Select β (18°–23°) based on wood species, moisture condition, and veneer thickness.
Control α by maintaining an appropriate rear-face contact width (hardwood 2–3 mm, softwood 2–4 mm).
Verify cutting geometry using δ = β + α.
Use the machine structure parameters to calculate ε, then determine the installation setting using θ = α + ε.
As the log becomes smaller during peeling, gradually reduce α within a reasonable range to maintain stable veneer output.
Hummingbird Machinery continues to support customers with commissioning, operator guidance, and process optimization to help veneer and plywood lines run consistently and efficiently.
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