Ten Reasons Internal Cracks Deserve More Attention Than They Get
Internal checking is the defect that survives every inspection and appears when the material has already absorbed most of its cost.
Internal cracks occupy an awkward position in wood quality control. Everyone knows they exist, most drying literature covers them, and yet they are rarely part of a routine quality regime. The reason is straightforward and worth stating at the outset: the technologies installed in wood processing lines today do not detect them. Everything that follows is a consequence of that one gap.
Internal checking is the defect that survives every inspection and appears when the material has already absorbed most of its cost.
Internal cracks occupy an awkward position in wood quality control. Everyone knows they exist, most drying literature covers them, and yet they are rarely part of a routine quality regime. The reason is straightforward and worth stating at the outset: the technologies installed in wood processing lines today do not detect them. Everything that follows is a consequence of that one gap.
10
Reasons.
1. They are a predictable consequence of drying physics, not of carelessness.
2. They have no surface signature
3. Drying quality standards explicitly exclude them
4. Neither camera nor X-ray scanning finds them — and this is the main reason they persist
5. Every finishing operation turns them into visible defects
6. Resawing turns every internal crack into a surface crack
7. They damage both appearance and performance
8. They are almost never isolated
9. Modification processes increase exposure
10. Found early, cracked material still has value
The Common
Thread.
Internal checking is not a defect that inspection performs badly. It falls between the scopes of the methods in use: drying assessment measures moisture, camera systems examine surfaces, X-ray measures density. The crack is none of those things, which is why it survives all three and appears later at planing, at resawing, or at the customer.
Closing the gap therefore means two things. A method aimed at the defect itself, placed as early in the process as the material allows — and a record of where and when cracks occur, because the schedule that caused them is still running.
Internal checking is not a defect that inspection performs badly. It falls between the scopes of the methods in use: drying assessment measures moisture, camera systems examine surfaces, X-ray measures density. The crack is none of those things, which is why it survives all three and appears later at planing, at resawing, or at the customer.
Closing the gap therefore means two things. A method aimed at the defect itself, placed as early in the process as the material allows — and a record of where and when cracks occur, because the schedule that caused them is still running.
References and
Further Reading.
Denig, J., Wengert, E.M. and Simpson, W.T. (2000). Drying Hardwood Lumber. General Technical Report FPL-GTR-118. USDA Forest Service, Forest Products Laboratory, Madison, WI. DOI: 10.2737/FPL-GTR-118. (Drying stress, honeycombing and collapse.) READ
Bergman, R. (2021). Drying and control of moisture content and dimensional changes. In: Wood Handbook — Wood as an Engineering Material. General Technical Report FPL-GTR-282. USDA Forest Service, Forest Products Laboratory, Madison, WI. READ
Ward, J.C. et al. (1972). Honeycomb and Ring Failure in Bacterially Infected Red Oak Lumber after Kiln Drying. Research Paper FPL-165. USDA Forest Service, Forest Products Laboratory, Madison, WI. READ
McMillen, J.M. and Wengert, E.M. (1978). Drying Eastern Hardwood Lumber. Agriculture Handbook No. 528. USDA Forest Service, Forest Products Laboratory, Madison, WI. (Drying degrade, including internal checking.) READ
EN 14298. Sawn timber — Assessment of drying quality. CEN, Brussels. (Note the stated exclusion of checks, shakes, warp and stain from its scope.) READ
EN 1611-1. Sawn timber — Appearance grading of softwoods. CEN, Brussels. READ
Erkennung von Innenrissen ab 5 µm Breite. timber-online.net, July 2017. (Trade press; discusses the difficulty of recognizing internal cracks with visual and X-ray scanning.) READ
Scheurendetector. Houtwereld, May 2017. (Trade press; Dutch-language account of internal crack formation during growth, drying and modification.)
Denig, J., Wengert, E.M. and Simpson, W.T. (2000). Drying Hardwood Lumber. General Technical Report FPL-GTR-118. USDA Forest Service, Forest Products Laboratory, Madison, WI. DOI: 10.2737/FPL-GTR-118. (Drying stress, honeycombing and collapse.) READ
Bergman, R. (2021). Drying and control of moisture content and dimensional changes. In: Wood Handbook — Wood as an Engineering Material. General Technical Report FPL-GTR-282. USDA Forest Service, Forest Products Laboratory, Madison, WI. READ
Ward, J.C. et al. (1972). Honeycomb and Ring Failure in Bacterially Infected Red Oak Lumber after Kiln Drying. Research Paper FPL-165. USDA Forest Service, Forest Products Laboratory, Madison, WI. READ
McMillen, J.M. and Wengert, E.M. (1978). Drying Eastern Hardwood Lumber. Agriculture Handbook No. 528. USDA Forest Service, Forest Products Laboratory, Madison, WI. (Drying degrade, including internal checking.) READ
EN 14298. Sawn timber — Assessment of drying quality. CEN, Brussels. (Note the stated exclusion of checks, shakes, warp and stain from its scope.) READ
EN 1611-1. Sawn timber — Appearance grading of softwoods. CEN, Brussels. READ
Erkennung von Innenrissen ab 5 µm Breite. timber-online.net, July 2017. (Trade press; discusses the difficulty of recognizing internal cracks with visual and X-ray scanning.) READ
Scheurendetector. Houtwereld, May 2017. (Trade press; Dutch-language account of internal crack formation during growth, drying and modification.)
Solutions
Solutions
Solutions