Tear-out is the torn, chipped or fuzzy surface left when wood fibres lift out instead of being cut off cleanly. It shows up as small pits on a planed board, ragged edges on a crosscut, chips on the back of a drilled hole or a rough patch in a figured grain. It is always the same event: the fibres were cut in a direction that left them unsupported. Change the direction, support the fibres, or make the cut shallower, and the surface comes out clean.
Read the grain
Look at the edge of a board. The grain runs in long lines that rise toward the face as they travel along the board. To plane without tear-out, cut so the tool is moving up the slope of the lines, from the lower end toward the higher, which means the fibres are supported ahead of the cutting edge. This is planing with the grain. Against the grain, the edge of the tool gets under the fibres and lifts them before they are cut.
A rule that holds well: stroke in the direction that makes the grain lines on the edge point away from you in the direction of travel, like fur stroked down the back. If a board tears in one direction, turn it around and plane from the other end.
Planing
- Set the blade finely. A thin shaving lifts less fibre. Take shavings under 0.05 mm on difficult wood.
- Close the mouth. A narrow gap in front of the blade holds down the wood just before the cut, which stops fibres from lifting.
- Keep the edge keen. A dull edge crushes and tears the fibre. A fresh edge slices it.
- Skew the plane at an angle to the stroke, which lowers the effective cutting angle and gives a slicing action.
- Use a higher angle. A bevel-up plane with a 50 or 55 degree bed, or a scraper plane, takes very fine cuts on wild grain. Steeper angles reduce the lift at the expense of effort.
- Use a card scraper for the last pass on figured wood. A scraper cuts tiny shavings from any direction, and is the standard finish for curly maple and birdseye.
Interlocked grain, found in sapele and some other tropical woods, reverses direction from one layer to the next. No single direction is clean. A high-angle plane, a scraper and sandpaper are the answers.
Crosscutting
Tear-out on a crosscut shows up on the back of the board where the blade exits. To avoid it:
- Put a sacrificial board behind the workpiece so the fibres have support at the exit.
- Score the line with a knife before sawing, and saw on the waste side.
- Use a fine-toothed blade with a high tooth count for plywood and melamine, as it cuts more times per inch.
- Cut slowly as the blade leaves the wood.
- Apply a strip of masking tape over the cut line to hold down the surface fibres.
Routing
A router bit cuts with a rotating edge, and for each pass there is a climb direction and a conventional direction. The standard direction, moving against the bit's rotation, is predictable. On end grain and cross grain there is a risk of breaking out at the end of the cut. Fixes:
- Rout end grain first, then long grain, so that any break-out is removed by the second cut.
- Take shallow passes, increasing depth gradually. A deep cut in one go tears the wood.
- Use a backing block behind the workpiece at the exit.
- Use a spiral bit, which shears the fibres as it cuts, leaving a cleaner surface than a straight flute.
Drilling
Drilling leaves a torn edge on the exit side. Clamp a scrap board under the piece, and drill through into it. A brad-point bit gives cleaner holes than a twist bit. A Forstner bit makes flat-bottomed holes with clean edges. Slow the drill as the bit breaks through.
Sanding
Sanding can tear soft woods when the grit is coarse and the pressure heavy. Sand with the grain, step through grits without skipping more than one, and stop when scratches from the previous grit are gone. Cross-grain scratches show when a finish is applied, especially oil. A block keeps the surface flat, so the sandpaper does not dig into soft growth rings.
Plywood and veneer
The face veneer on plywood is very thin, and it chips at the exit of a saw cut. Cut with the good face down on a table saw or up with a hand saw or circular saw, so the teeth enter the good face. Scoring the line before sawing, and covering it with tape, prevents the chips.
Species that tear
| Wood | Behaviour |
|---|---|
| Pine | Soft, tears in springwood near knots |
| Red oak | Open pores, tears on quarter-sawn faces |
| Curly maple | Reversing grain, tears in patches |
| Sapele | Interlocked, tears in ribbon stripes |
| Cherry | Usually clean, burns rather than tears |
| Basswood | Clean, soft, fuzzes when dull |
The woods database notes how each species works, and the species tool gives a guess with workability notes from a photo of a board, which helps when you have an unknown piece and want to plan your cuts.
Fixing tear-out after it happens
A small pit can be filled with glue mixed with fine dust from the same wood, sanded flush. A larger patch can be cut out and replaced with a matching piece, called a dutchman. For a very rough planed surface, start again with a scraper set at a slight angle, working across the torn area, then sand.