Hardwoods are generally sold to the industrial market as random width and length rough kiln dried lumber. Rough lumber typically ranges in
width from 3" to 12" and from 4' to 16' in length. The majority will be in the 5" to 8" widths and 8' to 12' lengths.If solid boards wider than 6" are needed they should be glued up from pieces no
wider than 3 ½" to obtain the necessary width. Single piece boards over 6" wide are prone to warping and should not be used unless adequately supported to prevent warp. A wide board made up of several
narrower boards glued edge to edge will provide a flat and warp resistant piece. Lumber mills cut hardwoods to standard thicknesses as shown in the chart below
Industry Designation |
Nominal Thickness |
Maximum Finished Thickness |
4/4 |
1" |
13/16" |
5/4 |
1 ¼" |
1 1/16" |
6/4 |
1 ½" |
1 5/16" |
8/4 |
2" |
1 ¾" |
10/4 |
2 ½" |
2 ¼" |
12/4 |
3" |
2 ¾" |
16/4 |
4" |
3 ¾" |
Hardwood lumber should normally be kiln dried to between 6% and 8% moisture content to ensure satisfactory results. Hardwood lumber with moisture contents above 8% will generally shrink and crack as
they age. Moisture contents below 6% interfere with good machining and enable the wood to take on moisture and swell as they age.
Hardwood Lumber Grades
Hardwood lumber grades are established by private lumber associations. Typically the rules favor maximized returns for the lumber producers and not necessarily for the end users.
Typical Hardwood Lumber Grades Are:
The grade of lumber reflects the quality of the entire board and should not be used to define the quality of lumber required for a given part.
Many times a perfectly acceptable part can be cut out of a lower grade material at significant cost savings. This is called "Defect Cutting" of lumber where the clear pieces are cut out of the board
while the knots, splits, wormholes, etc. are discarded.The grade of lumber to be used should be determined by the wood manufacturer with the end user or designer defining what the finished
part must look like. Please see " Solid Wood Cutting Grades
" for help in determining what cutting grade should be specified for a given part. |
