Moisture Content / Lumber Shrinkage 
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Foot Board Measure 
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Target Size 
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Fibre Recovery Percentage 
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Lumber Recovery by Diameter 
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Lumber Recovery:
 
Foot Board Measure
1 fbm (foot board measure) is equal to a board 12" wide x 12" long x 1" thick.  Fbm is calculated as thickness (inches) x width (inches) x length (feet) / 12.
  • Thickness and width used in the fbm calculation are nominal (2x4, 2x6) although the finished size may be 1.500 x 3.500, 1.500 x 5.500, etc.
  • A 2x4x8' would equal 5.33 fbm
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Target Size
Lumber green target size must allow for:
  • Sawing deviation - this can vary by equipment (+/- 0.015" to +/- 0.040")
  • Shrinkage - varies by species and moisture content
  • Planing - <.050" per face (varies with sawing deviation)

Green target sizes will have a direct effect on lumber recovery.  Reducing saw kerf and sawing deviation will allow decreased green target sizes which will increase lumber recovery.

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Fibre Recovery Percentage
Net lumber recovery for a 1st quartile northern softwood sawmill with an average log top diameter of 6.0" (15 cm) could be up to 304 fbm/m3 or 8.6 fbm/ft3 or .47 m3/m3.  Log quality, target sizes, saw kerfs and wane allowances will all effect maximum lumber recovery.  In this example the fiber recovery distribution is:
  • Finished lumber (kds4s) 47%
  • Chips 34%
  • Sawdust & chip fines 9%
  • Shrinkage 4%
  • Shavings 6%
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Lumber Recovery by Diameter
Lumber recovery generally increases as the log size increases.  The graph shows the relationship between log size (top diameter) and lumber recovery.
  • For FBM/M3 multiply FBM/FT3 by 35.3
  • For M3/M3 multiply FBM/FT3 by .065 (rough green production)
  • For Diameter in CM multiply Inches by 2.54
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