UK CNC Wood Processing Service Guide

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  Key takeaways
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  Which wood material suits your part
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  Grain direction and toolpath choices in UK CNC wood processing
• 4
  Moisture content and why it decides your tolerance
• 5
  Setting realistic tolerance bands for wood parts
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  Machine setup and workholding for wood
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  Sanding, sealing and finishing after machining
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  Step by step: preparing a UK CNC wood processing order

Wood is not a homogeneous block. Every board has a grain direction, and the cutter meets it differently on each pass. Route with the grain and the tool lifts clean fibres. Route across it and you get tear-out at the exit edge. On a 3-axis machine the fix is simple: rotate the nesting layout so the finishing pass runs with the grain, and leave 0.3–0.5 mm of radial stock for a light cleanup cut.

Climb milling versus conventional milling matters more on wood than on aluminium. Climb milling on a down-cut spiral bit pushes fibres down into the cut and gives a cleaner top edge on veneered panels. On solid timber with reversing grain, a compression spiral bit handles both faces at once. That single tool choice can remove a sanding step.

Spindle speed and feed rate scale with density. Softwoods such as pine run at 18,000 rpm and 6–8 m/min. Hardwoods like oak or beech want 12,000–15,000 rpm and 3–5 m/min with a chipload of 0.1–0.2 mm per tooth. Push the feed too high and the edge burns. Push it too low and the tool rubs, which dulls carbide fast.

Cut depth is the other lever. A 12 mm compression bit should not take 12 mm in one pass. Two passes at 6 mm each hold edge quality and reduce spindle load. Deep single passes are the most common cause of delamination on plywood and of chatter marks on solid stock.

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  Down-cut spiralClean top face on veneer and melamine.
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  Compression spiralClean both faces, one pass, fewer setups.
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  Up-cut spiralBest chip evacuation in deep pockets.
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  Straight fluteCheapest option, worst edge on cross-grain cuts.

Every wood part you machine will keep changing size after it leaves the machine. A 300 mm oak panel can grow or shrink 2–3 mm between a dry winter workshop and a humid summer. If your drawing calls for ±0.2 mm on that panel, no machine will hold it for long. The tolerance has to match the material behaviour, not the machine capability.

Ask for the moisture content before the first cut. Kiln-dried interior stock should sit at 8–10% MC. Exterior joinery stock often runs 12–15% MC. If the supplier cannot tell you the MC of the batch, they are guessing at the feed rate and the fit. A pin meter reading takes seconds and prevents a whole batch of warped parts.

Acclimatisation matters too. Stock that arrives at the workshop on Monday and is cut on Monday will move after cutting. Letting it sit 48–72 hours in the machining bay brings it close to equilibrium. For tight-fit joinery, that wait is cheaper than remachining.

Design around movement where you can. Use slots instead of round holes for cross-grain fixings. Leave a 0.5–1 mm expansion gap on panel edges that sit in a frame. These are drawing decisions, and they cost nothing at the CAD stage.

Metal shops quote ±0.005 mm without blinking. Wood shops should not. The material itself moves more than that in an afternoon. What you can control is the tolerance of the machined features against a stable datum, measured in the workshop at the time of cutting.

For CNC-routed sheet goods, ±0.2 mm on profile and hole position is achievable on a good nesting router with a vacuum bed. For solid timber, ±0.3–0.5 mm is a sensible band on cross-grain features. For long parts over 1,000 mm, add 0.1 mm per 300 mm for thermal and moisture drift unless the workshop is climate controlled.

Feature type changes the number. A bored hole for a dowel or a bearing needs a tighter band than a decorative edge profile. A rebate that takes a panel needs to match the panel thickness, which itself varies. Specify the fit, not just the dimension: 'rebate to suit 18 mm nominal panel, clearance 0.2 mm' tells the machinist more than '18.2 mm'.

Where a tight fit is genuinely needed, plan a test cut. One test piece in the actual stock costs far less than a full run that does not assemble. Any supplier working on wood should offer that as standard.

Wood panels are usually held on a vacuum bed during nesting. That works well for flat sheet up to 4,000 mm long, provided the panel is flat and the bed is sealed. Thin panels under 6 mm can lift at the edges and chatter. The fix is a spoil board with a fresh skim and a smaller nest layout so each part sits inside the sealed zone.

Solid timber is a different problem. Screws and clamps leave marks, and the part is often a one-off. A common approach is to machine a sacrificial fixture from MDF that matches the part profile, then hold the timber in that. It takes one extra setup but holds the part rigid for a 5-axis cut.

For curved work, 5-axis machines with a Ø400 mm rotary table let you tilt the part and reach undercuts without repositioning. That matters for chair components, handrail sections and sculptural work where the profile wraps around more than one face. On a 3-axis machine the same part needs two or three setups and a re-datum, and each re-datum adds error.

Dust extraction is not optional. Fine wood dust is a health hazard and it also packs around the cutter, causing heat and poor finish. A supplier running wood should have extraction at the cutter and a filtered shop system. Ask about it. It tells you how seriously they treat the process.

A CNC router leaves a machined surface, not a finished one. The visible finish comes from sanding and coating, and those steps change dimensions. Sanding removes 0.05–0.1 mm of material. A sealer plus two topcoats adds 0.1–0.2 mm of build on a flat face. If a panel must slot into a frame, account for that build on the drawing.

Grit sequence matters. On hardwood, start at 120 grit to remove tool marks, then 180, then 240 if a clear finish is specified. Skipping the 120 step leaves scratches that the topcoat magnifies rather than hides. On MDF, 180 to 240 grit is enough; going finer burnishes the surface and the paint will not key.

Edge treatment is where most wood parts fail in service. Sharp routed edges chip. A 0.5–1 mm radius or a small chamfer on every exposed edge gives the coating something to hold and removes the weak corner. It costs a few seconds of machine time.

If the parts go outside or into a wet area, the coating system has to match. Interior lacquer on an exterior part will fail within a season. Say where the part will live, and the finish specification follows from that.