Flat sawing

After an initial cut through the diameter of a log, parallel cuts produce flitches: strips of lumber with consistent thickness.[2] Two cuts on each flitch trim the bark from the sides, and reduces it to a standard board width with squared edges. Two more cuts at each end set the length.

Lumber can be quickly flat-cut with a side-by-side set of mechanical saws.[3] A slower but sturdier method involves passing the log back and forth over a single saw.

To reduce buckling that may occur along the middle of flat-cut boards, the initial cut may be offset from the diameter, and resulting sections cut further before cutting the flitches.

Flat-sawn wood often exhibits "flat-" or "slash grain", where the angle between the visible growth rings and the width of the board is 45° or less.[4] This makes the wood vulnerable to deformation as it dries, or if later exposed to moisture. Flat-sawn wood is less stable than quarter sawn or rift sawn wood, but can be produced more quickly and at lower cost.[5]

The face of the board may show curved grain, sometimes with intricate patterns.