Which Bits to Buy for Wood CNC Machine?

• 1
  Router bit families at a glance
• 2
  Bits for wood cnc machine: upcut and downcut first
• 3
  Compression bits and when they pay for themselves
• 4
  V-bits, ball nose and 3D carving
• 5
  Shank size, carbide grade and collet fit
• 6
  Matching feed, speed and depth of cut

Most wood routing problems trace back to one decision: which way the chips leave the cut. An upcut spiral lifts chips out of the groove, so the tool runs cooler and the pocket clears itself. The trade-off is a fuzzy top edge on veneered board, because the top fibers are unsupported when the flute shears them.

A downcut spiral pushes chips down into the cut. That presses the top veneer against the core and leaves a clean, splinter-free edge on both faces of thin material. The cost is chip evacuation. On deep pockets you have to slow the feed and rely on strong dust extraction, or chips get re-cut and the edge burns.

For 18 mm plywood with a veneer face, a downcut is usually the right call for the last pass. For 40 mm solid oak, an upcut clears the groove and keeps the tool alive. Many shops keep both in the same diameter so they can swap without touching the tool table.

Chip load is the number that matters more than spindle speed. On a 6 mm two-flute upcut in hardwood, 0.05–0.10 mm per tooth at 16,000–18,000 rpm is a workable starting window. If the chips come out as dust, you are rubbing, not cutting.

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  UpcutBest chip clearance, fuzzy top edge on veneer
• 2
  DowncutClean top edge, poor clearance in deep pockets
• 3
  Two-fluteGeneral woodworking default, good balance
• 4
  Three-fluteBetter finish at higher feed in MDF and plywood

A compression bit combines both geometries on one tool. The tip is upcut, the upper section is downcut, so the bottom of the cut and the top of the cut are both sheared toward the middle. On double-sided melamine or veneered plywood this removes the need for a separate finishing pass on the second face.

The catch is depth. The downcut section only engages once the tool is buried past the upcut length, typically 6–10 mm depending on the tool. If your material is 12 mm and you cut in two passes of 6 mm, you never reach the compression zone and the top edge will still tear out.

That is why compression bits suit nested-based panel work more than light trimming. They cost more and they are less forgiving of shallow passes, but on a run of 200 cabinet sides they save a flip operation and a second fixture.

On tool life, coatings matter as much as geometry. A plain carbide bit in MDF wears on the edge within a few sheets. A TiN or AlTiN coating runs cooler and holds the edge longer. Neither coating changes the cut geometry, so choose the geometry first.

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  Use it whenDouble-faced panels, one-pass edge quality
• 2
  Skip it whenCut depth never reaches the downcut section
• 3
  CoatingsTiN and AlTiN reduce heat and extend life
• 4
  HoldingCheck runout before blaming the bit

V-bits cut a chamfer or a groove whose width depends on depth. A 90° V-bit at 1 mm depth cuts a 2 mm wide line; at 3 mm depth it cuts 6 mm. That linear relationship is useful for lettering and inlays, and it is also the reason a small Z-axis error shows up as a visibly wrong line width.

Ball nose bits are the workhorse for 3D relief and mold patterns. The radius sets the smallest detail you can resolve. A 6 mm ball nose with a 10 percent stepover, 0.6 mm, will leave a surface that needs light sanding. Push the stepover to 30 percent and the scallops are visible without a scraper.

Both bit types cut with the side of the tool as much as the tip, so they need a rigid setup. A 3 mm ball nose hanging 40 mm out of the collet will chatter in hardwood no matter what feed you pick. Shorten the gauge length first.

For pattern and mold work that feeds into metal casting, the surface you leave on the pattern transfers to the mold. A 0.6 mm stepover on a 6 mm ball nose plus light hand finishing is usually enough for a sand-cast pattern. Tooling that has to hold ±0.005 mm is a different process, and that is where we come in.

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  V-bitDepth controls line width, keep Z calibrated
• 2
  Ball noseRadius sets detail, stepover sets finish
• 3
  Gauge lengthKeep it short to avoid chatter
• 4
  Pattern workFinish carries through to the mold surface

Shank diameter is set by the cut, not by the spindle you own. A 3.175 mm shank is fine for 1–2 mm detail bits and light trimming. Anything cutting 12 mm deep in hardwood wants a 6 mm or 12.7 mm shank, because the shank stiffness, not the cutting edge, limits how hard you can push.

Solid carbide covers almost all wood routing. High-speed steel bits are cheaper but lose the edge quickly in MDF, which is abrasive. If you cut a lot of MDF, expect to replace or resharpen carbide on a schedule rather than waiting for a bad cut.

Collet and nut condition matter as much as bit quality. Runout above 0.02 mm will break small bits and leave a poor wall finish. Clean the collet taper, seat the bit with at least 70 percent of the shank in the collet, and check runout with a dial indicator before a long run.

Balance the whole assembly. A large-diameter bit in a worn nut at 24,000 rpm will vibrate even if the bit itself is perfect. If the sound changes when you change tools, the problem is often the holder, not the cutter.

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  3.175 mmDetail and trimming only, light depth
• 2
  6 mmGeneral pocketing and profiling
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  12.7 mmDeep cuts, heavy material removal
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  RunoutKeep under 0.02 mm for small bits

Start from chip load, then work back to feed rate. Feed in mm per minute equals spindle rpm times flutes times chip load. For a two-flute 6 mm bit at 18,000 rpm and 0.06 mm per tooth, that is about 2,160 mm/min. If your machine cannot hold that feed, reduce rpm rather than grinding the bit at low feed.

Depth of cut follows rigidity. A 6 mm bit in plywood can take one pass at 1× diameter, 6 mm, on a stiff gantry. On a lighter hobby machine, 3 mm passes are safer. The symptom of too much depth is a screaming cut and a tapered wall, not a broken bit.

Ramp or helical entry beats plunging straight down. A straight plunge concentrates heat at the center of the tip where surface speed is near zero. A 3° ramp spreads the load and roughly doubles tool life in hard material.

Listen to the cut and read the chips. Fine dust means you are rubbing. Brown chips mean too much heat. Loose, warm chips that break cleanly mean the window is right. Adjust one variable at a time so you know what changed.

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  Chip load0.05–0.10 mm per tooth in hardwood
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  Depth1× diameter on a rigid machine
• 3
  EntryRamp at 3° instead of plunging
• 4
  SignalDust means rubbing, brown means heat