The Top 5 Forests of CNC Processing
Ash, cherry, walnut, maple and cedar are the woods most often sent to a CNC mill, and each one behaves differently under the cutter. This guide is for engineers and buyers choosing a wood grade before a prototype or a production run. Read it and you will know which species fits your part, which one will fight you, and what to check on the quote.
Key takeaways
The 5 forests of CNC processing compared
Ratings assume kiln-dried stock at 8–12% moisture content, cut with sharp carbide tooling.
| Species | Grain and hardness | Best for | Watch out for |
|---|---|---|---|
| Ash | Open, uniform, medium-hard | Engraving, routing, bent forms | Fuzzy edges on climb cuts |
| Cherry | Fine, closed, medium density | Inlays, furniture faces, trim | Burns if feed rate is too low |
| Walnut | Coarse, dark, dense hardwood | Structural parts, handles, panels | Higher cost, visible grain shift |
| Maple | Fine, light, dense hardwood | Jigs, fixtures, cutting boards | Hard spots deflect small tools |
| Cedar | Soft, fibrous, aromatic | Outdoor trim, deck parts, frames | Tears out, poor thread strength |
Pick the species from the exposure, not the photo
Choose ash or maple when you need crisp detail and stable fixtures, cherry when the finish is the product, walnut when the part carries load, and cedar only where weather resistance matters more than strength.
How each forest behaves under the cutter
Ash cuts clean when the tool stays sharp and the chipload stays above 0.1 mm per tooth. Its open grain means the cutter shears fibers instead of crushing them, so deep pockets and 3D reliefs come out crisp. Run a finishing pass at 12,000–16,000 rpm with a 6 mm two-flute carbide bit and you get an edge that needs light sanding only. Climb cutting on ash can lift fibers on the exit side, so leave 0.2 mm of stock and take it in a conventional finishing pass.
Cherry is the easiest of the five to finish but the least forgiving on heat. Feed too slowly and the bit polishes the surface until it glazes and burns. Keep the chipload steady, use down-cut tooling on the top face, and cherry will hold Ra-level smoothness without sanding sealer. It also moves less after machining than ash, which matters on long panels or drawer fronts where a 0.5 mm warp shows.
Walnut is dense and abrasive. It dulls carbide faster than the other species here, so budget for a tool change on runs above a few hundred parts. In return it holds a 6 mm thread without inserts, machines thin walls down to about 3 mm, and takes a dark oil finish that hides minor tool marks. The downside is cost and color variation between boards, which is a real problem on visible assemblies.
Maple is the hardest common choice and the most stable. That combination makes it the default for jigs, fixtures and vacuum tables where the wood itself has to hold tolerance. Small cutters deflect in maple's hard spots, so reduce step-down to 0.5 × tool diameter and keep the tool overhang short. Cedar sits at the other end: soft, light and naturally rot-resistant, but it crushes under clamps and cannot hold a thread worth trusting.
Tolerance, moisture and grain direction
Wood is not metal, and the tolerance you can hold depends on moisture as much as on the machine. Kiln-dried stock at 8–12% moisture content moves about 0.2–0.3% across the grain for every 1% change in moisture. On a 300 mm wide panel that is roughly 0.6 mm of seasonal movement. If your drawing calls for ±0.1 mm on a wood part, the material will decide that, not the CNC.
Grain direction drives surface quality more than spindle speed. Cutting across the grain produces clean shearing; cutting into rising grain lifts fibers and creates tear-out. On ash, cherry and cedar, plan the toolpath so the finishing pass travels with the grain on visible faces. On walnut and maple the effect is smaller but still visible under a clear finish.
Dust extraction is not optional. Wood dust is combustible, and fine sanding dust from walnut and cedar is a known respiratory irritant. Any shop running wood on a CNC needs chip collection at the cutter, not just a floor sweep. That is also why many metal-focused suppliers decline wood work entirely, or run it on a separated cell.
What to verify before you place a wood order
Ask what the supplier actually cuts. A shop set up for aluminum and stainless will have the spindles and the metrology, but its dust handling, workholding and fixturing may not suit wood. A vacuum table or a spoilboard setup with low clamping pressure is what keeps thin panels flat. If the supplier only offers vises, expect chatter on anything thinner than 12 mm.
Ask how the stock is conditioned. Wood that arrives at 15% moisture and gets machined the same day will shrink after shipping. A supplier who stores stock in a controlled area and lets it equalize before cutting is a better bet than one who quotes the lowest number. This is the single most common reason a wood part fails inspection weeks after delivery.
Ask about the finish schedule. Sanding to 180 grit, then 220, then a sealer is normal for furniture-grade parts. Skipping sealer and going straight to stain produces blotchy cherry and maple. On cedar, an oil or penetrating sealer keeps the natural rot resistance working; a thick film finish will crack as the wood moves.
Finally, ask what tolerance the quote assumes. Wood parts are usually quoted at ±0.5 mm on machined features and ±0.2 mm on hole positions, with the caveat that moisture movement is excluded. If a supplier quotes ±0.05 mm on a wood part, the number is marketing, not metrology.
Step by step: from species choice to shipped part
- 11. Match species to exposureIndoor furniture and fixtures: ash, cherry, walnut or maple. Outdoor or damp service: cedar, or a hardwood with a proper exterior finish. Do not spec cedar for a threaded joint.
- 22. Fix the moisture targetSpecify kiln-dried stock at 8–12%. Ask the supplier to confirm with a pin meter before cutting. Anything above 12% will move after machining.
- 33. Set realistic tolerancesUse ±0.5 mm on profiles and ±0.2 mm on hole positions for wood. Reserve ±0.005 mm for metal parts; wood cannot hold it across seasons.
- 44. Plan toolpaths around grainFinish with the grain on visible faces. Leave 0.2 mm stock for the finishing pass on ash and cedar. Reduce step-down to 0.5 × tool diameter on maple.
- 55. Control feed and speed6 mm two-flute carbide at 12,000–16,000 rpm for finishing. Keep chipload above 0.1 mm per tooth to avoid glazing and burn on cherry.
- 66. Specify the finish and sealSand 180 then 220 grit, apply sealer before stain on cherry and maple. Use penetrating oil on cedar so it can still breathe.
- 77. Inspect before packingCheck moisture, grain run-out on visible faces, and hole positions. Ask for inspection reports if the parts feed an assembly line.
Questions buyers ask about wood CNC parts
Which of the 5 forests of CNC processing is cheapest to machine?
Ash and maple are usually the lowest-cost options because they machine fast and are widely available in kiln-dried boards.
Cherry and walnut cost more per board and walnut dulls tooling faster, which adds to the per-part price on longer runs. Cedar is cheap as a material but slow to cut cleanly because of tear-out.
Can a CNC shop hold ±0.05 mm on wood?
No. Wood moves with humidity, so the material sets the limit, not the machine. A realistic callout is ±0.5 mm on profiles and ±0.2 mm on hole positions.
If your design needs tighter than that, switch to aluminum or a dimensionally stable plastic such as POM or PEEK.
What is the minimum order quantity for wood parts?
At GreatLight there is no minimum order quantity. We run from one prototype to 10,000+ part runs.
Wood prototypes usually ship in 3–5 days once stock and tooling are confirmed, and we return a quotation with free DFM analysis within 12 hours.
Will you sign an NDA for a wood product design?
Yes. Uploads are secure and confidential, and we sign an NDA on request before reviewing drawings.
This applies to furniture concepts, packaging fixtures and any consumer product where the shape is the value.
Which species should I avoid for threaded holes?
Cedar is the weakest choice for threads because its fibers crush instead of holding. Ash is workable but benefits from a threaded insert.
Walnut and maple hold a 6 mm thread far better, and maple is the most reliable of the five for repeated assembly.
Do you machine wood and metal in the same shop?
We run 127 high-precision CNC machines across three plants, mainly for metals and engineering plastics.
Wood work is quoted case by case depending on geometry, quantity and finish, and we will tell you honestly if the part is better suited to another process.
Send the drawing and we will tell you which wood works
Upload your file and get a quotation with free DFM analysis within 12 hours, plus a straight answer on tolerance and species.
12-hour quoteNo minimum order quantity100% inspection before shipmentNDA on request
More machining notes
We publish setup notes, tooling trials and inspection data from the factory floor.
