Why Is My Plywood Tearing Out?

Read the damage first

Plywood is thin veneer layers glued in alternating grain directions. The face veneers are the fragile part: unsupported at the cut line and easy to lift. Before changing anything, look at which face failed, because that single observation identifies the cause.

Why compression spirals are the default for sheet goods

A compression bit carries two opposing helixes. The lower section is upcut and the upper section is downcut. In a through-cut, the upcut portion works against the bottom veneer and lifts it into the panel; the downcut portion works against the top veneer and presses it into the panel. Both faces are held in compression at the point of cut, which is exactly what a laminated material needs.

The one way to get this wrong: making the first pass shallower than the upcut section. Compression bits typically have an upcut length of about one bit diameter. Cut shallower than that and only the upcut portion engages — the tool behaves like a plain upcut bit and fuzzes the top face, which is confusing when you have just bought a bit specifically to prevent it. Take the first pass deeper than the upcut tip, or choose a mortise-style compression bit with a short upcut section for dados and pockets.

When upcut or downcut is the right answer

Upcut clears chips aggressively and holds the bottom veneer against the spoilboard. Choose it when the underside is the show face, when you are cutting deep slots that need chip evacuation, or when the top edge will be hidden or edge-banded. Expect some top-face fuzz — that is the trade.

Downcut presses the top veneer down for a crisp top edge. Choose it for shallow dados, pockets and engraving where you never break through. It packs chips into the cut, so keep depth per pass at or below one bit diameter and use good dust extraction.

Compression is for through-cuts where both faces matter — cabinet parts, furniture components, anything visible on two sides.

Chipload for plywood and sheet goods

Fuzzing is not always a geometry problem. A bit that rubs instead of shearing will bend fibres over and leave them standing rather than cutting them off, which reads as fuzz even with a correct compression bit.

These are LMT Onsrud's published figures for a single-flute compression spiral, by material and bit diameter:

Chipload = feed rate ÷ (RPM × flutes). A common real-world error: 18,000 RPM, 90 IPM, 2 flutes gives 90 ÷ 36,000 = 0.0025″ — about a sixth of what a 1/4″ bit in plywood should be taking. Corrected to 0.015″, the same setup needs 18,000 × 2 × 0.015 = 540 IPM. If the machine cannot feed that, drop to 12,000 RPM and run 360 IPM for the identical chip — lowering RPM is almost always better than crawling the feed.

The same figures drive our Cut Doctor and feed rate calculator, and appear per size on each bit's product page.

Technique fixes beyond the bit

• Onion-skin the final pass. Leave 0.010″–0.015″ of material and clear it in a light finishing pass. The part stays supported until the very end, which eliminates most bottom-face blowout and tab tear.
• Climb-cut the finish pass. A shallow climb pass of 0.020″ or less shears grain toward the material rather than levering it outward — the most effective single trick for figured or splintery ply.
• Resurface the spoilboard. A grooved, uneven spoilboard leaves the bottom veneer unsupported exactly where it needs backing. This is a surprisingly common cause of bottom-face tearout.
• Improve hold-down. Any lift under vacuum or tabs turns a clean cut into a chattering one.
• Rotate dull tooling sooner. Plywood glue lines are abrasive; edge sharpness degrades faster than in solid wood, and a dull edge fuzzes regardless of the numbers.

Bits for clean plywood edges

Browse CNC router bits for plywood & MDF, compression router bits, or downcut spirals. The Bit Finder will match a bit to your panel thickness and which faces need to be clean.

Common questions

What is the best router bit for cutting plywood without tearout?

A compression spiral, for any through-cut where both faces show. It is the only common geometry that protects the top and bottom veneers simultaneously. For shallow dados that never break through, a downcut spiral gives a cleaner top edge at lower cost.

Why does Baltic birch tear out more than regular plywood?

It does not usually — but its many thin plies and void-free construction make any tearout far more visible, and Baltic birch is often used precisely where exposed edges are the design feature. The same compression geometry and chipload targets apply; expectations are simply higher.

Can I fix fuzzy edges by slowing down?

Almost never, and it usually makes things worse. Slowing the feed reduces chipload, which increases rubbing — the exact mechanism that bends fibres over instead of cutting them. If the surface looks rough, check the chipload arithmetic before reaching for the feed override.

Does spindle RPM matter as much as feed rate?

Only through their ratio. Chipload depends on feed divided by RPM times flutes, so raising RPM without raising feed reduces chip thickness and can cause fuzzing and burning. When your machine limits feed rate, lowering RPM is the correct move.

Chipload ranges reflect manufacturer application data for solid carbide tooling across our catalogue. Verify on scrap, and adjust for your machine's rigidity and hold-down. Every bit we sell lists its own recommended feeds and speeds on its product page.