CNC Timber Machining Services

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  Key takeaways
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  Where CNC timber machining fits
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  What to send with your timber RFQ
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  What CNC timber machining services actually control
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  Tolerances you can hold on timber
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  Tooling, fixturing and the cost drivers
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  Finishing and how machining affects it
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  How to judge a CNC timber supplier
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  Step by step: from drawing to timber part

A CNC router does not care whether the blank is aluminium or ash. The cutter follows the toolpath at the programmed feed, and the material decides what happens next. In timber, the same cutter that leaves a mirror finish on 6061 will lift fibers along the grain and burn them on the climb side if the chipload is wrong. That is the core problem of CNC timber machining services: the machine is rigid, the material is not uniform.

Grain direction is the first variable. Cutting with the grain gives clean shearing. Cutting against it lifts fibers. Cutting across the end grain is where most tear-out happens, and no feed rate fully solves it. A 2-flute compression bit at 12,000–16,000 rpm with a 3–6 m/min feed is a common starting point for plywood and MDF, but solid oak usually wants a slower feed and a shallower depth of cut to keep the edge intact.

Moisture content is the second variable. Kiln-dried stock at 8–12% MC behaves predictably. Green or poorly stored stock moves after machining, so a part that measured 300.0 mm on the bed can measure 298.5 mm a week later. For any part with a fit, ask the supplier to confirm MC and to store blanks in the same shop environment before cutting.

Species hardness sets the tool life curve. Softwoods like pine and cedar cut fast but fuzz. Hardwoods like maple, oak and walnut hold detail better but dull carbide sooner. Engineered boards sit in between: MDF machines cleanly and takes paint well, while plywood exposes glue lines that wear edges and can chip at the veneer.

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  Grain directionPlan toolpaths so the cutter shears with the grain on visible faces.
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  Moisture contentTarget 8–12% MC and stabilize blanks before machining.
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  Species hardnessHarder wood holds detail but shortens cutter life.
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  Board thicknessNominal 18 mm stock is rarely 18.00 mm; measure before programming.

General machining tolerances on metal at GreatLight run to ±0.005 mm. Timber cannot hold that, and no honest supplier will claim it can. The reason is not the machine. It is the material: wood swells and shrinks with humidity, springs back after the cutter passes, and varies in density within a single board. A realistic drawing tolerance for machined timber is ±0.2 mm on a stable engineered panel and ±0.5 mm on solid hardwood.

Where precision still matters, control it with a secondary operation. Machine the pocket 0.3 mm undersize, then finish it on a second pass after the part has acclimated. Use a fixture that references the same datum for both passes. This is how you get a repeatable fit on a wooden insert without fighting the material.

Datums matter more than the tolerance number. Wood moves most across the width, so a datum on a long edge will drift. Put the primary datum on a short, stable face and locate from a machined pocket rather than an as-sawn edge. If the drawing calls out a 0.1 mm flatness on a 600 mm solid oak panel, expect a conversation about grain, not a guarantee.

For parts that must mate with metal hardware, machine the timber oversize and the metal to print. Let the wood be the compliant side of the joint. This is standard practice in furniture and instrument work, and it removes most of the fit risk without adding cost.

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  Engineered panels±0.2 mm is realistic on MDF and quality plywood.
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  Solid hardwood±0.5 mm is a fair target for most furniture parts.
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  Two-pass finishingRough 0.3 mm oversize, then finish after acclimation.
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  Datum choiceReference a machined pocket, not an as-sawn edge.

The cutter list tells you a lot about a shop. Straight flute and up-cut bits clear chips well but leave a rough top edge. Down-cut bits protect the top face and pack chips into the cut. Compression bits combine both and are the default for double-sided panels where both faces are visible. A 6 mm compression bit is common for panel work; 12 mm and larger are used where chip clearance matters more than detail.

Fixturing is usually the largest hidden cost in a timber job. Vacuum tables work well on flat panels but lose grip on warped boards and small parts. A dedicated fixture or a machined nest adds setup time, and that time appears in the quote. If your part is small or has a complex outline, expect the supplier to price a fixture, not just cutting time.

Depth of cut should stay conservative. A rule of thumb for solid hardwood is one cutter diameter per pass at full width, less if the grain is figured. Aggressive passes cause deflection, chatter and burn marks that sanding will not remove. On MDF and plywood you can take deeper passes because the material is uniform and the chips clear predictably.

Tool changes and part re-fixturing add time without adding value. Design parts so one setup covers most features. Group features on one face. If a part needs machining on six sides, ask whether a 5-axis setup or a simple re-fixture is cheaper for your quantity.

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  Compression bitsDefault for panels with two visible faces.
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  Vacuum vs fixtureVacuum suits flat panels; fixtures suit small or warped parts.
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  Depth of cutOne cutter diameter per pass on solid hardwood.
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  Setup countFewer setups usually beat a lower hourly rate.

Machining sets the surface that finishing has to work with. A clean cut at the right chipload leaves fibers intact and sands easily. A burned or torn surface needs more sanding, and sanding changes the geometry you just machined. That is why the cutting parameters should be chosen for the finish, not only for cycle time.

Typical as-machined timber surfaces sit around Ra 3.2–6.3 μm depending on species and cutter. Metal parts at GreatLight can reach Ra 0.2–0.8 μm, but that number does not transfer to wood. If your drawing specifies a fine surface finish on timber, translate it into a sanding grit and a coating system instead. 120–180 grit is normal before sealing; 220 grit or finer before a clear lacquer.

Coating choice changes dimensions. A thick lacquer or a two-part epoxy build can add 0.1–0.3 mm to a face. If the part fits into a metal frame, machine the timber undersize by the expected coating thickness, or mask the mating faces. Talk to the finishing team before you release the drawing.

For outdoor parts, the finish is the life of the part. End grain absorbs water fastest, so seal it. A supplier who machines and finishes in the same shop can control that sequence. If machining and finishing are split across vendors, someone has to own the fit after coating.

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  Sanding sequence120–180 grit before sealing; 220+ before clear coat.
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  Coating buildAllow 0.1–0.3 mm per coated face.
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  End grainSeal it; it absorbs moisture fastest.
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  One ownerKeep machining and finishing under one roof where possible.

Ask what machines will run your part. A shop with 16 simultaneous 5-axis machining centers, 12 four-axis mills and 27 three-axis machines can choose the right platform instead of forcing your job onto one machine. For timber, a 3-axis router with a 4,000 × 400 × 150 mm travel handles long architectural parts; a 5-axis center handles sculpted geometry that would need three fixtures otherwise.

Ask how they hold the part. The answer tells you whether they have machined wood before. If the reply is only about clamps and vise jaws, the setup may crush softwood or leave marks on a visible face. Good timber shops talk about vacuum zones, sacrificial spoilboards and soft jaws.

Ask about inspection. GreatLight inspects 100% of parts before shipment and can supply reports on request. On timber, inspection should include moisture reading, key dimensions and a visual check for tear-out and burn. A supplier who only measures the outside profile is not checking the features that matter.

Ask about certifications and process control only where they apply. ISO 9001:2015 and IATF 16949:2016 cover quality management. ISO 13485:2016 applies to medical device work and ISO 27001:2022 to information security. These matter if your timber part sits inside a regulated assembly or your drawings are confidential. Uploads are secure, and an NDA is available on request.

Finally, ask for the DFM notes. A quotation and free DFM analysis within 12 hours is a useful signal. If the feedback points at grain direction, tool reach or coating thickness, the supplier is reading the part, not just the file.

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  Machine fitMatch the platform to part size and geometry.
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  Hold-down planVacuum zones and soft jaws protect visible faces.
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  Inspection scopeMoisture, dimensions, tear-out and burn.
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  DFM feedbackSpecific notes on grain and tooling are a good sign.