How to inspect incoming lumber | Woodworking Network

Q. We buy a lot of lumber and have been getting more concerned about what characteristics we should be aware of and should inspect for.

A. The characteristics of the incoming lumber affect yield, processing costs, and ultimate performance of the cabinets, furniture and other wood products that are manufactured. Many of these characteristics are not well covered in the standard grading rules, so only monitoring lumber grade and footage will be inadequate.

Discussion of characteristics
Lumber grade and footage greatly affect the yield (or volume) of parts, the quality of parts and time to process the lumber into parts. You should receive the full range of quality allowed within a grade; that is, another lumber customer should not have received the best quality within the grade and you received the lower quality.

My experience also shows that footage measurements are often incorrect; usually the actual footage is lower than the value on the invoice.

Moisture content of the lumber must be at the correct level. If much drier than 6.0 percent MC, the wood will behave in a brittle manner when machining, and it will absorb glue rapidly, potentially leading to a poor glue joint in panels. If the lumber is much above 7.5 percent MC (perhaps above 8.0 percent MC, but I suggest 7.5 percent MC is better), the wood will shrink in processing (poor glue joints, un-smooth surfaces and joints), and potentially in use (delayed shrinkage with numerous potential problems).

The average MC must be correct, plus the variation of pieces around this average must be small. Of critical importance when measuring the MC is the core MC. As you are aware, it is the core that ends up in the product, not the shell.

The presence of shake, which is a separation that runs parallel (not across) the growth rings, indicates bacterially infected lumber. Usually the infection is only a foot or two up the lumber. The risk is honeycomb when drying, wet lumber (even though the rest of the piece is dry), and a foul odor that can persist in the final product especially in humid conditions (such as in a bathroom or near a kitchen sink). Such wood should not be used; chop off the end of the lumber before ripping.

The lack of end coating means that potentially 2 inches or more from the end or every piece of lumber will have to be trimmed off. (The risk is greatest with the denser species.) Further, as end checks are difficult to see as they move up the piece, it is possible that an end check might accidentally be included in a stave, leading to a small crack in the final product. With properly applied (mainly, put on thick enough) end coating, the trimming required will be 1/4 inches in most cases. For 8-foot lumber, this is a loss of 4 percent with no coating and 1/2 percent with coating; this 3-1/2-percent gain is worth about $25 per MBF or so, but the cost of applying the coating at the sawmill is only $4 per MBF.

The presence of large (over 1/4-inch wide) end splits indicates that there is stress in the tree that is also in the lumber and that will be in the components manufactured. If the humidity and moisture content of the wood products never changed, then this stress would not be an issue. But with changes in moisture, there is a strong likelihood that the wood will twist and warp lengthwise slightly. Further, when wood with stresses is machined, even though the machines, such as a planer or belt sander, are perfectly flat, the stress will cause immediate warp when machining — mostly bow or side bend.

The presence of side bend warp or twist warp in the raw lumber indicates the presence of stress, steep grain angles, and/or tension wood. All these characteristics within the wood will cause a slight amount of warp — bow, twist and side bend — in the components when machining and in the final product if and when the moisture changes.

The presence of cupping warp indicates that the wood is cut from near the center of the tree, which again means that some warp — bow, twist, cup and side bend can be expected if the moisture changes.

The lumber width, especially if narrow, increases the piece count and also reduces the overall yield. Both of these characteristics result in higher processing costs. The major concern would be for a load or bundle with quite a few narrow pieces. I would think that somewhere around 6 inches would be the dividing line. Of course, a few narrow pieces in every load would be normal. 
The lumber length is important, with longer lumber being less expensive to process.

The presence of checks and honeycomb in oak when looking at dry lumber indicates that the lumber was not dried properly and that yields will be lowered substantially. Checked lumber should be withdrawn from production and returned to the supplier for a full credit.

Any discoloration, including the presence of gray or pink discoloration in ash and maple, blue stain or sap stain, and sticker stain in most species, is preventable through proper handling and drying of the lumber. (So-called mineral stain, usually caused by an insect, occurs in the tree and is not controllable during sawing, or drying.) Oftentimes, such staining is not obvious from the rough lumber. 

When visible, the grade and price should be 2B Common, at best; or the lumber can be returned. When some pieces are stained, it is likely that more stain will be seen as processing proceeds.

The presence of drying stress (also called casehardening) will cause immediate warp when machining and will make flatness of panels and doors difficult to achieve. 

Such stress can be easily removed in the dry kiln during normal drying procedures. The presence of such stresses indicates poor drying and often highly variable final moisture contents, along with other drying defects.

The presence of the correct grain, including quartersawn grain, absence of sapwood, and so on is important.