IS 656:1988 is the Indian Standard (BIS) for logs for plywood. This standard covers the requirements for timber logs intended for the manufacture of plywood. It outlines the suitable species, dimensional measurements, grading categories, and permissible defects for logs used in rotary peeling or slicing into veneers.
Logs for Plywood
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Log Grade Designation | Grades A, B, C, D based on defect levels. | 'Special Selection', 'First Grade', 'Second Grade', with criteria varying by species. | JAS for Logs (2007) |
| Volume Calculation Method | Quarter-girth formula: V = L x (G/4)² | Huber's formula (mid-diameter based) is the reference method: V = L x (π/4)d_mid² | EN 1309-2:2006 |
| Girth / Diameter Measurement Point | Girth measured at the mid-point of the log. | Mid-diameter is the reference measurement; rules for using end-diameters are also provided. | EN 1309-2:2006 |
| Minimum Girth / Diameter (Top Grade) | Minimum mid-girth of 60 cm (approx. 19 cm diameter) for Grade A logs. | Minimum top-end diameter varies by species, e.g., 14 cm for Sugi and Hinoki logs. | JAS for Logs (2007) |
| Knot Allowance (Top Grade Example) | Grade A: Sound knots up to 50 mm dia, max one per meter length. No unsound knots. | JAS 'Special Selection' (Sugi): Sound knots up to 30 mm dia, number limited by log diameter. | JAS for Logs (2007) |
| End Split Allowance (Top Grade) | Grade A: Not to exceed 50 mm in length at each end. | Often defined by the severity and length relative to log diameter, e.g., 'not passing through the heart'. | General US Veneer Log Grading Rules |