What Machining Tolerances Can PEEK & PTFE Achieve?
Engineers selecting PEEK or PTFE components routinely ask how tight a tolerance they can realistically hold. The short answer: CNC-machined PEEK and PTFE parts can typically achieve tolerances in the ±0.005–0.1 mm range, but the achievable value depends on material, part size, feature geometry, and process control. This article breaks down tolerance capability into practical grades, explains what drives the limits, and gives design advice.
1. The Short Answer
- PEEK (unreinforced and CFR/GF): machined tolerances down to approximately ±0.005–0.05 mm on well-defined features, with ±0.02–0.1 mm as common general practices.
- PTFE: typically ±0.05–0.13 mm — PTFE is softer and more compliant, so very tight tolerances are harder and costlier to hold.
- Moulded parts: depend on the mould and shrinkage control, usually coarser than machined.
Industry-wide, quoted "tight" machining for engineering plastics is realistically around ±0.005–0.1 mm depending on feature and material.
2. Tolerance Capability by Grade
| Material | General machining tolerance | Notes |
|---|---|---|
| --- | --- | --- |
| Unreinforced PEEK | ±0.02–0.1 mm | Stable, machines cleanly |
| CFR-PEEK (LY-205, LY-501) | ±0.02–0.1 mm | Achievable; watch edge integrity |
| GF PEEK (LY-200) | ±0.05–0.15 mm | Abrasive fibres can affect finish |
| PTFE (LY-401/403/405) | ±0.05–0.13 mm | Soft/compliant — looser typical |
| Polyimide PI (LY-601) | ±0.02–0.1 mm | Rigid, machinable |
These are general guidance ranges (comparable across the industry) — confirm the specific achievable tolerance with your vendor for your exact part.
3. What Drives the Limit
Several factors pull tolerance in different directions:
- Material stiffness and CTE — PEEK's thermal expansion and relaxation after machining must be managed (stress relief / annealing).
- Part size — larger parts accumulate more dimensional change.
- Feature geometry — deep slots, thin walls, and tight internal corners are harder to hold.
- Machining process control — speeds, feeds, coolant, and tool condition matter a lot for plastics.
- Measurement method — CMM vs gauge vs optical can read differently at tight tolerances.
4. A Tolerance Selection Table
| Requirement | Suggested tolerance class | Guidance |
|---|---|---|
| --- | --- | --- |
| Critical mating feature | ±0.005–0.02 mm | Use CNC machining, specify datum & CMM method |
| General precision feature | ±0.02–0.05 mm | Typical precision machining |
| Standard machined part | ±0.05–0.1 mm | Cost-effective general tolerance |
| PTFE soft features | ±0.05–0.13 mm | Looser, avoid over-specification |
| Non-critical features | ±0.1–0.2 mm | Loosen to cut cost |
The cost of tight tolerance rises sharply as the class tightens — loosen non-critical tolerances to keep cost low.
5. Design-for-Tolerance Advice
To hit the tolerances you need without overpaying:
- Tighten only critical features — put ±0.01 mm where it matters, ±0.1 mm elsewhere.
- Define datums — agree which surfaces are reference points before inspection.
- Add radii at internal corners — sharp internal corners are stress concentrators and hard to machine precisely in CFR-PEEK.
- Consider the material's behaviour — PTFE is softer; if you need tight PTFE tolerances, confirm feasibility early.
- Specify measurement method — agree CMM/optical conditions to avoid disputes.
6. Machining vs Moulding Tolerance
| Route | Typical tolerance | When |
|---|---|---|
| --- | --- | --- |
| CNC machining | ±0.005–0.1 mm | Precision, low-mid volume |
| Injection/compression moulding | Coarser, mould-limited | High volume, complex geometry |
| Extruded stock | Stock-shape tolerance | Rod/tube/sheet that you machine further |
For the tightest features, machining from certified stock is usually the way to go; moulding is best suited to high-volume, less-tolerance-critical parts.
7. Verification Matters
A tolerance claim is only as good as the measurement:
- Request a dimensional inspection report covering all critical features.
- Confirm the measurement method (CMM, gauge, optical) matches the drawing's inspection notes.
- For CFR-PEEK, verify machined-edge fibre integrity, not just dimensions.
Summary
CNC-machined PEEK can achieve tolerances down to about ±0.005–0.1 mm, with PTFE typically looser (±0.05–0.13 mm) due to its softness. Tightening tolerances increases cost, so specify tight classes only on critical features, define datums and measurement methods, and verify with inspection reports. Dalian Luyang (www.newmaterialchina.com), ISO 9001 & ISO 13485, machines PEEK, CFR-PEEK, PTFE, and PI components for seals, inserts, and electrolyser frames — with documented inspection to back every tolerance.
Frequently Asked Questions
- What is the tightest tolerance PEEK can be machined to? CNC-machined PEEK can typically hold about ±0.005–0.05 mm on well-defined features, with ±0.02–0.1 mm as common general practice.
- Why can't PTFE hold as tight tolerances as PEEK? PTFE is softer and more compliant, so it deforms more during machining; typical PTFE tolerances are around ±0.05–0.13 mm.
- Should I specify tight tolerances everywhere? No — tightening tolerances raises cost sharply. Apply tight classes only to critical mating features and loosen the rest.
Related Topics
- CNC Machined Parts Procurement Checklist for PEEK & PTFE
- Custom vs Standard PEEK Parts: When OEM Engineering Pays Off
- PEEK Sheet, Rod & Plate: What to Check in Your Machining Stock
Dalian Luyang Technology Development Co., Ltd. (www.newmaterialchina.com) manufactures PEEK, PI, and PTFE precision parts — seals, inserts, machined components, and electrolyser frames — under ISO 9001 and ISO 13485. Established 2006. Contact: liyulong@luyangkeji.com · WhatsApp +86 15989781752. This guide is educational reference material; always verify against your chosen grade's official datasheet.