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How to deal with tearout in hard maple July 9, 2026 | 1:07 pm CDT

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Wood Dr

Solid Wood Machining

How to deal with tearout in hard maple

Gene Wengert

July 9, 2026 | 1:07 pm CDT

Gene Wengert (1942-2025) was popularly known as “The Wood Doctor.” He trained thousands of people in efficient use of wood for more than 50 years.

Editor’s note: This column originally published in 2021 was produced before Gene Wengert died in 2025. It is printed here in memoriam.

Q I have some hard maple that is giving me a lot of small spot tearout or maybe you call it chipped grain. What is the cause and cure?

A There are likely two issue that individually would not cause a problem, but together they combine to create this tearout issue. We need to do a little detective work.

Appreciate that hard maple has a lot of small pockets of swirly grain. In fact, when it gets really bad, we call it bird’s eye. So, with these swirls, we are planing with the grain for a moment and then against the grain for another moment. So, the risk of tearout with maple is high due to the species characteristics. Both machining must be close to perfect, and wood properties affected by drying must be under control. Also, even the processing variables not mentioned here must correct. That is, we can minimize the risk, working on both fine-tuning our machines and man-affected wood properties. Remember to look for two possible items that our out of “normal.”

Machine issues When a knife comes in contact with the wood, if the blade itself is too slender (large rake angle), the knife will behave like a chisel or wedge with the wood failure traveling ahead of the knife, following the grain. Eventually, the knife will begin to exit the wood and a big hunk of wood (magnified view) will be broken or chipped out. This chipped piece will leave a hole or void in the wood if the grain at this point was diving into the wood that we want to be smooth; that is, if we were planing against the grain.

A second machine concern is that the knife needs to really sharp. HHS is probably a better knife for obtaining a smooth surface, compared to carbide.

A small depth of cut and a slower feed speed will also provide a better surface. Or maybe I should say that deep cuts and fast feed will encourage chip out. Of course, feeding too slowly and taking too light a cut will create heating, fast dulling, and compressed fibers that create a rough surface, including grain raising, during finishing. 

Wood issues There are two things we can do in drying of lumber that will make the wood quite brittle and subject to tearout. First, we can over-dry the wood in the kiln. Even though we can equalize and try to bring the moisture content up to a higher value, the brittleness is still there. The best advice is to never run the kiln under 5.0% EMC at any point in the cycle, Kiln operators know the terminology, but what it means is that no piece will dry under 5.0% moisture content.

The other contributor to brittleness in drying is to use a kiln temperature over 160F.

NHLA Rules for sidebend in hardwood lumber say a piece of lumber of any grade must be on the same axis and cannot curl around and along the lumber piece with sidebend.

Q We are getting a lot of grade hardwood lumber with sidebend. I know that sidebend is affecting our yields. How much sidebend can lumber have? How about cup?

A Sidebend, also called crook or lengthwise warp, is indeed a serious factor affecting yield of long pieces. Cup is a serious factor affecting the yield of wider pieces.

Sidebend: The NHLA Rules for hardwood lumber are based on the volume of rectangular, clear areas, called clear cuttings. All these cuttings, for a piece of lumber of any grade, must be on the same axis.  This means that they cannot curl around and along the lumber piece with sidebend. (See drawing.). With sidebend lumber, just an inch or two of sidebend can easily make the clear area smaller and unable to make the best grade; that is, drop the lumber grade.

Cup: The NHLA Rules for cup require, for FAS, FAS One Face, and Select grade lumber under 12-inch-wide that the entire piece must be able to be planed or surfaced (using an imaginary planer in the grader’s mind) to a standard uniform thickness. This rule means that the amount of cup in the best grade of lumber must be very slight, especially if the lumber is not overly thick.

For No.1 Common, and lower grades, the rules require that only the clear cutting areas used to establish the grade must be able to be surfaced to standard thickness. In this case, each clear cutting is considered separately. In effect, some cupped lumber can be tolerated in lower grades without changing the grade of the piece.

Standard thickness for 2/4 to 7/4 lumber is 1/16 inch thinner than the nominal; for instance 4/4 (or one-inch thick) lumber has a standard kiln-dried thickness of 15/16 inch. There are other limits for quartersawn and for thicker lumber.

Q What are some concerns about using urban lumber?

A One big concern with urban lumber is that there can be metal or other foreign objects in the wood that can damage equipment.  It is also common to have damaged roots, which allow bacteria and maybe insects and fungi into the tree. Avoid green or non-kiln dried lumber. Make sure the kiln goes above at least 145F.  

Bacteria also weaken the wood and present special issues in drying that the kiln operator may not understand. 

Urban wood often has many branches, so the highest grades of lumber are not abundant. Further, stains from pruning, metal screws, cutting the wood and bark, etc. are common. Some urban producers do not grade their lumber. In addition to the temperature used in drying, there are expectations for the final MC average and final moisture variation, stress relief, flatness and so on.

Have something to say? Share your thoughts with us in the comments below.

About the author

Gene Wengert

Gene Wengert (1942-2025) was popularly known as “The Wood Doctor.” He trained thousands of people in efficient use of wood for more than 50 years and authored foundational resources on wood technology. He worked at the University of Wisconsin-Madison and Virginia Tech. His popular "Wood Doctor's Rx" column has appeared regularly in FDM and FDMC magazine since 1978. Because so much of his advice was timeless, he asked that we continue to run his columns in memoriam.

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