Guides / Choosing a Supplier
Carbon Fiber Machining Explained for Engineers and Buyers
Carbon Fiber Machining editorial team · October 20, 2026
Key points
- Most carbon parts are routed from cured plate with diamond-coated or PCD cutters. Waterjet is used for thick plate and large outlines.
- Typical profile tolerance is ±0.1 mm, and ±0.05 mm is achievable on good routers. Thickness tolerance comes from the plate, not the machining.
- Delamination at holes and edges is the main quality risk. Sharp tools, backing on the exit side and the right feed control it.
- A DXF at 1:1 plus a PDF with plate type, thickness, cosmetic side and tolerances gets the fastest firm quote.
Carbon fiber machining means cutting, drilling and trimming cured carbon fiber reinforced polymer (CFRP) into finished parts. Most of it is CNC routing of flat plate: a spindle with a diamond-coated cutter follows the outline and holes from a DXF. The rest is tube work, cutting and cross drilling carbon tubes, and trimming of molded parts, where a cured 3D shell gets its edges and holes on a fixture.
The material behaves like neither metal nor plastic. It is abrasive, it does not deform before it breaks, and it is built from layers that can peel apart at a careless cut. That is why the method, the tool and the support under the part decide the result more than the machine brand.
This guide covers what you need to know to buy machined carbon parts: methods, materials, realistic tolerances, the defects to look for and what to put in your RFQ.
What makes carbon fiber hard to machine
A carbon plate is a stack of thin plies. Each ply is a layer of carbon fibre, woven or unidirectional, held in a hard epoxy resin. The plies are laid at different angles, for example 0°, +45°, -45° and 90°, so the plate is stiff in every direction. Every cut goes through all of them.
Three things follow from that structure:
- Tool wear. Carbon fibre is abrasive. An uncoated carbide end mill can lose its edge within a few metres of cut. Shops use diamond-coated carbide or PCD (polycrystalline diamond) tools that last many times longer.
- Fraying and splintering. Fibres at the top and bottom face have nothing above or below them. A cutter that pulls them outward leaves fuzz and splinters. Compression cutters, with up-cut and down-cut flutes, push both faces inward.
- Delamination. The resin between plies is the weak link. Drilling thrust or a dull cutter can split the plies apart at a hole or an edge. On a structural part that lowers strength around fasteners.
Dust is the fourth factor. Carbon dust is fine and electrically conductive. Shops cut it with extraction right at the spindle, or wet, to protect the machine electronics and the people in the shop.
Cutting methods compared
| Method | Best for | Typical tolerance | Limits |
|---|---|---|---|
| CNC routing | Plate up to about 10 mm, holes, slots, pockets | ±0.05 to ±0.1 mm | Inside corners take the cutter radius |
| Abrasive waterjet | Thick plate, large simple outlines | ±0.1 to ±0.2 mm | Edge taper, pierce damage, small holes drilled after |
| 5-axis machining | Trimming and drilling molded 3D parts | ±0.1 to ±0.2 mm on trim | Needs a fixture per part shape |
| Laser | Rarely used on structural parts | Not recommended | Burns the resin, toxic fumes |
Typical values for planning. The shop that quotes you confirms what it can hold on your part.
For a flat part from plate, routing is the default. It cuts the outline, holes and slots in one setup and leaves an edge that only needs light sanding. Waterjet is useful when the plate is thick or the sheet is large and the shape is simple. Shops often waterjet the blank and finish holes and fits on a router. More detail on each part family is on the pages for sheet and plate cutting, tube machining and drilling and trimming.
Materials you will be asked about
Shops will ask what plate or tube you want. The main families:
- Woven plate (3K twill or plain weave). The common choice for brackets, drone frames and panels. The woven face ply holds a routed edge well and looks the part.
- UD or quasi-isotropic plate. Unidirectional plies stacked at several angles. Stiffer for the weight than woven plate, but a UD face ply splinters along the fibre at the cut, so tooling matters more.
- Roll-wrapped tube. Plies wrapped at several angles around a mandrel. It takes cross holes and slots well.
- Pultruded tube and rod. All fibres run lengthwise. Straight, stiff and cheaper, but cross holes and slots can split it.
- Forged carbon. Short chopped fibres pressed in resin. It machines more like a filled plastic and does not fray, so it suits 3D shapes and small features.
The face finish (gloss, matte or peel ply) comes from the plate maker. Machining does not change it, but handling can scratch it, so say which face is cosmetic. Our guide to choosing a carbon fiber machining shop covers how to check that a shop stocks or can buy the plate you need.
Tolerances that are realistic
Carbon parts are often over-toleranced, because drawings are copied from aluminium parts. Some numbers to plan with:
| Feature | Typical | Achievable with care |
|---|---|---|
| Routed profile | ±0.1 mm | ±0.05 mm |
| Drilled hole diameter | ±0.05 mm | Reamed or interpolated, H8 class |
| Hole position | ±0.1 mm | ±0.05 mm |
| Plate thickness | Set by the plate, often ±0.1 to ±0.2 mm | Sorted or ground plate |
| Flatness of thin plate | Set by the plate | Depends on layup balance |
Typical values for routers with good fixturing. Not a promise.
Two points catch buyers out. First, thickness comes from the plate. A machine shop cannot hold ±0.05 mm on the thickness of a 2 mm press-cured plate. It can only sort sheets or grind the faces, which costs a lot. Second, thin plates with an unbalanced layup can bow after cutting releases stress. If flatness matters, ask for a balanced, symmetric layup. The design rules list hole sizes, edge distances and radii that keep parts cheap.
Defects to check on delivery
Look at every edge and hole under good light. The common defects:
- Exit-side delamination. A ring of lifted plies or fuzz around the back of a hole. Caused by drilling thrust without backing. Our guide to drilling carbon fiber without delamination explains how shops prevent it.
- Fraying on the edge. Loose fibres along the profile, usually from a dull or wrong cutter.
- Chipped corners and burn marks. Signs of too much feed or too little extraction.
- Scratches on the cosmetic face. From handling or from chips trapped under the plate during cutting.
Agree what is acceptable before the order. For cosmetic parts, a sample or a photo standard helps. For structural parts, some buyers set a limit on the damaged diameter around a hole compared to the hole size.
What to send in an RFQ
A complete RFQ gets a firm price the first time instead of a round of questions:
- DXF at 1:1 in millimetres for flat parts, closed outlines, no duplicate lines. STEP for tubes and 3D parts.
- A PDF with plate type and thickness, face finish, the cosmetic side, tolerances where they matter, hole types (clearance or fit) and edge finish.
- Quantity per order and per year. Repeat volume changes how a shop nests and fixtures the job.
- Material supply. Whether the shop buys the plate or you send your own.
- Deadline and the region where you want the shop to be.
Pricing follows plate cost, sheet use, cut length, holes and finishing. Our guide to carbon fiber CNC cutting cost breaks it down with a worked example.
Worked example (hypothetical)
A robotics team needs 200 gripper fingers per year, cut from 3 mm 3K twill plate, 95 x 28 mm with a pocket, four 3 mm holes and a 6 mm bearing seat. The drawing calls ±0.02 mm on every dimension, copied from the aluminium version.
The first quotes come back high. The shops price the ±0.02 mm on every edge as extra passes and inspection. After review, only the bearing seat needs a fit (H8, interpolated with a PCD tool) and the holes need ±0.05 mm. The profile goes to ±0.1 mm. The pocket radius changes from R0.5 to R1.5 so a 3 mm cutter can run. The revised drawing quotes noticeably lower and the parts do the same job.
How to pick a shop
Ask three questions. Does the shop cut carbon as regular work, or only now and then? Which tools does it use for carbon, and how does it back up holes? How is dust extracted? Shops that answer all three without hesitating are usually the ones that deliver clean parts.
If you have a drawing ready, send your RFQ and we match it with up to three shops that do this work every day.
Frequently asked questions
Can a normal CNC machine shop cut carbon fiber?
It can, but most general shops avoid it. Carbon wears standard carbide tools within minutes, frays without the right cutter geometry and produces fine conductive dust that damages machines and lungs without extraction at the spindle. Shops that cut carbon daily have the tooling and extraction set up.
What is the most accurate way to cut carbon fiber plate?
CNC routing with diamond-coated or PCD cutters. It holds ±0.1 mm on most profiles and ±0.05 mm with good fixturing. Abrasive waterjet is faster on thick plate but leaves a slight taper and typically holds ±0.1 to ±0.2 mm.
How thick can carbon fiber plate be machined?
Routers handle plate up to about 10 mm as normal work. Thicker laminates, up to 20 mm and more, are machined too, usually on stiffer machining centres or cut by waterjet and finished by routing.
Is carbon fiber dust dangerous?
Fine carbon dust is a respiratory irritant and is electrically conductive, so it can short electronics in the machine and the shop. Shops cut carbon with extraction at the spindle or wet, and operators wear respiratory protection.
Need a quote for a carbon part?
Send the DXF or STEP file. We match you with up to 3 shops that cut carbon fiber every day and reply within 24 business hours.
Get matched with a carbon shop