In this guide
End Checks in Woodturning Blanks: What Causes Them and When a Blank Is Still Usable
Small cracks on the end of a woodturning blank are commonly called end checks. Some are shallow enough to remove during blank preparation, while others extend farther into the wood and may make the blank unsuitable for the intended project.
Knowing how to evaluate these checks can help you avoid surprises on the lathe, use more of each blank, and recognize when saving a questionable piece is not worth the risk.
What Is an End Check?
An end check is a separation in the wood that normally begins on an exposed end-grain surface. It may appear as a thin line extending inward from an edge, corner, growth-ring boundary, or the pith.
Checks should not be confused with ordinary surface marks. A saw scratch crosses the wood fibers without separating them. A check is an actual opening between fibers and may continue beneath the visible surface.
End checks can occur in bowl blanks, spindle blanks, logs, boards, and partially completed turnings. They are especially common in green wood and blanks that have experienced rapid or uneven drying.
Why End Grain Dries So Quickly
Wood contains long cells that generally run parallel to the trunk. Moisture can move through the exposed ends of these cells more readily than it can move across the grain.
As a result, the ends of an unsealed blank may begin drying and shrinking while the interior remains wetter and larger. The dry outer wood is restrained by the wetter interior, creating stress. When that stress exceeds the wood’s strength, a check can form.
Wood is hygroscopic, meaning it exchanges moisture with the surrounding air. Temperature, relative humidity, species, grain orientation, thickness, and existing moisture content all influence that exchange. USDA Forest Products Laboratory: Moisture Relations and Physical Properties of Wood
Why Some Species Check More Readily
Not every species responds to drying in the same way. Several characteristics affect checking:
- Total shrinkage from green to dry
- Difference between radial and tangential shrinkage
- Density and strength
- Grain irregularity
- Growth stresses within the tree
- Extractives and natural oils
- Blank size and moisture content
Dense exotic woods can develop surprisingly fine checks that are difficult to see. Burl, crotch, curly, and highly figured blanks may contain grain that changes direction rapidly, creating localized drying stress.
This does not mean figured or dense wood should be avoided. It means these blanks deserve careful inspection and controlled storage.
The Pith Is a Common Trouble Area
The pith is the small central core representing the tree’s earliest growth. Wood surrounding it often contains juvenile wood and experiences considerable stress as it dries.
A crack that reaches the pith can spread outward along one or more radial lines. For that reason, bowl blanks are generally more stable when the pith has been completely removed.
Look closely at the growth-ring pattern. Even when the pith is just outside the blank, tightly curved rings may show that the piece was cut close to it. That area may require more careful drying and inspection.
In spindle blanks cut from small limbs, the pith may run through the entire length. Such blanks can still be useful for certain projects, but they have a higher chance of splitting as moisture changes.
How Deep Does the Check Go?
The visible opening is not always the entire defect. A check may narrow until it becomes nearly invisible while continuing farther into the blank.
To evaluate one:
- Clean the end grain so dirt and rough saw marks do not hide the crack.
- Use strong light from several directions.
- Mark the visible end of the check with a pencil.
- Trim a small amount from the blank.
- Reinspect the freshly cut surface.
- Continue until the check disappears completely.
Do not assume that removing only the visibly open portion has eliminated the problem. A faint hairline may remain beyond it.
Compressed air can clear dust from a crack, but eye protection is essential. Avoid probing aggressively with a metal tool, which may enlarge the opening or make its true shape harder to judge.
When a Checked Blank May Still Be Usable
A blank with a minor end check may remain useful if the defect can be removed without entering the planned project.
A checked spindle blank might be shortened. A bowl blank might be reduced slightly in diameter, shifted off-center, or assigned a shallower profile.
Before cutting, draw the intended project directly on the blank. Include:
- Finished diameter or length
- Expected wall position
- Tenon or recess
- Foot and rim
- Waste needed for mounting and truing
This reveals whether the check lies entirely in disposable material or extends into the finished turning.
A 12-inch bowl blank that must be reduced to 10 inches may still make an excellent bowl. A peppermill spindle with a check at one end may become a bottle stopper, handle, box, or ornament blank instead.
Matching the project to the sound wood is often better than forcing the original plan.
When to Reject or Heavily Reduce a Blank
Do not mount a blank merely because a crack looks small from the outside. Set it aside or reduce it substantially when:
- The crack remains after repeated trimming
- It extends toward the intended chucking area
- It crosses the proposed bowl wall
- It reaches deeply toward the center
- Multiple checks divide the blank into sections
- Tapping produces movement or an opening along the crack
- Bark, decay, or insect damage intersects the check
- The crack appears to widen when light pressure is applied
- You cannot confidently determine its depth
A crack in rotating wood is a structural concern, not simply a cosmetic defect. Centrifugal force, cutting pressure, vibration, and continued moisture change can cause it to lengthen.
Filling a structural crack with adhesive or decorative resin does not automatically make a blank safe to turn. If a repair is considered, the remaining wood must still be capable of safely holding together throughout the turning process.
When uncertain, choose another blank.
Preventing New End Checks
End checking is easier to prevent than repair.
Seal Fresh End Grain Promptly
Apply a purpose-made end-grain sealer to freshly cut green blanks as soon as practical. The coating slows moisture loss from the ends so drying can proceed more evenly.
For round bowl blanks, coat the exposed end-grain areas thoroughly. For spindle blanks, seal both ends.
The goal is not to stop drying permanently. It is to reduce the severe moisture gradient that causes the ends to shrink far ahead of the interior.
Store Blanks Away from Direct Heat
Avoid placing green blanks in direct sun, near a heater, or where strong dry airflow strikes one surface. Rapid drying can increase checking, particularly during the early stages.
The USDA Forest Products Laboratory notes that correct drying, handling, storage, and moisture control can minimize problems caused by dimensional change. USDA Forest Products Laboratory: Drying and Moisture Control
Maintain the Sealer
End coating can be damaged during handling. Inspect stored blanks occasionally and recoat exposed areas as necessary.
Leave Extra Length
When processing logs into spindle stock, allow extra material at both ends. If checking develops, the affected portion can be removed without sacrificing the entire project.
Remove the Pith
When practical, cut bowl blanks so the pith is outside the usable blank. The small loss in available diameter is usually worthwhile compared with the increased possibility of a major radial split.
Checks in Rough-Turned Bowls
A rough-turned green bowl can also check if its rim, base, or end-grain sections dry too quickly.
Use an even wall thickness so no area remains much wetter than another. Avoid leaving a heavy base beneath a thin wall, and round over sharp rim edges slightly. Depending on the drying method, the bowl may be coated, bagged, packed in shavings, kiln-dried, or placed in a controlled environment.
Inspect rough bowls periodically. A small new check may sometimes be removed during final turning, but only if enough sound material remains.
Inspect Every Blank Before Mounting
Even a blank that was sound when purchased can change during storage. Before every turning session:
- Examine all faces under bright light.
- Look for changes around the pith, bark inclusions, knots, and voids.
- Check previously sealed ends.
- Confirm that the mounting area is solid.
- Rotate the blank by hand after mounting.
- Begin at an appropriately low speed and stand out of the line of fire.
If a crack becomes visible while turning, stop the lathe and investigate. Do not continue simply to see whether it gets worse.
Use the Sound Wood, Not the Whole Blank
An end check does not always ruin a turning blank, but it should never be ignored. Clean the surface, determine how far the defect extends, and design the project entirely within sound wood.
Sometimes the best decision is to shorten the blank or make a smaller bowl. Other times, the safest and most economical choice is to reject it.
A slightly smaller finished turning is always better than taking an unnecessary chance with a compromised blank.
