PEEK CNC Machining: What Tolerances Can PEEK Actually Hold?

PEEK moves with heat and moisture in ways metals do not, and a tolerance that is easy on aluminium becomes a fight on PEEK. Buyers who specify metal tolerances on PEEK parts get scrap. This guide sets the tolerance expectation on the material's real behaviour.

Why PEEK tolerances differ from metal

PEEK's lower stiffness and its sensitivity to heat and moisture mean a feature cut perfectly can drift as the part relieves stress or equilibrates humidity. A tolerance held on the machine is not the tolerance held on the bench a day later.

You should expect PEEK tolerances to be specified with this behaviour in mind. The factory behind this guide machines PEEK on the same 100+ CNC machines (Mazak, Brother, TSUGAMI, Sodick) and measures on the in-house Hexagon CMMs, but reports the as-received condition honestly, not a machine-only number.

What holds well and what does not

Machined PEEK can hold tight linear dimensions on the cut; what suffers is flatness over large areas, thin walls that deflect, and threads that relax. You should concentrate tolerance where the function lives and relax it where PEEK cannot hold it.

You should ask the shop which features it would treat as critical on PEEK and which it would relax, exactly as on metals. The discipline of marking critical tolerances applies doubly to a material that moves after the cut.

Annealing and residual stress

PEEK parts carry residual stress from machining that releases over time and moves dimensions. Annealing before critical machining relieves it upfront, so the finished part is stable rather than still settling. Skipping anneal buys a drift you meet later.

You should specify anneal for tight-tolerance PEEK and ask the shop to confirm it in the process. A shop that anneals and re-measures has controlled the stress; one that cuts and ships has deferred the problem to your assembly.

Environment and the moisture variable

PEEK absorbs a little moisture and changes dimension with it, so a part measured dry and assembled humid will not match. You should state the service environment and ask the shop to measure in the condition the part will see.

You should also consider stabilising the part before measurement. The factory can condition PEEK to a target humidity before the in-house Hexagon CMMs report, so the number reflects service, not the lab, and the tolerance means what it says.

Setting PEEK tolerances collaboratively

You should send the tolerance intent with the drawing and ask the shop to propose a PEEK-realistic band. A shop that proposes relaxed flatness and held linear dimensions is reading the material; one that quotes metal tolerances blindly will fail at first article.

If you collaborate on the band, you get a part that passes and functions, rather than a number that looks right on paper and drifts in hand. The tolerance on PEEK is a negotiation with the material, not a decree.

Annealing protocol and tool geometry for PEEK

PEEK is not aluminium with a different colour, and the difference shows up at the inspection bench, not on the data sheet. The material holds residual stress from the cast billet, and every cut releases a little of it. A part machined dry and measured on a Hexagon CMM at 20 °C will measure one set of numbers; the same part left overnight and re-measured can move by tens of microns because the stress relaxes. If you order PEEK without an anneal plan, you pay for that movement in scrap.

The workable sequence is to rough-machine the blank, send it through a controlled anneal cycle — ramp, soak, and cool at rates matched to the section thickness — then finish-machine the annealed blank. A shop that runs PEEK straight from billet to finishing is gambling with the tolerance band, and the gamble shows up in the first-article report as flatness drift the drawing never allowed for.

Tool geometry is the other lever. PEEK likes sharp, polished, positive-rake cutters with a low helix on milling and a high positive rake on turning. A dull edge rubs, builds heat, and pushes the material instead of shearing it; the surface then shows smeared patches that look like a finish problem but are a tool problem in disguise. The feed rate has to keep the chip thickness meaningful — too light and the cutter rubs, too heavy and the thin chip welds back to the parent surface. Coolant matters too: flood coolant works, but air-blast alone is often cleaner for PEEK because it avoids the thermal shock a cold fluid applies to a hot cut.

Where the tolerance band is tight, you should ask the shop to specify the anneal cycle, the tool geometry, and the measurement condition in the quote, not just the final dimension. A quote that lists only the finished size has skipped the three decisions that decide whether the part passes or drifts. The facility behind this guide runs 100+ CNC machines including Swiss-type turning at ±0.002 mm and 3/4/5-axis milling at ±0.003 mm on Hexagon CMMs, with Ppk ≥ 1.67 on key characteristics at initial study and Cpk ≥ 1.33 in production, so the band and the evidence are available together. Ask for the anneal plan alongside the capability evidence; the answer separates a shop that has run PEEK from one that intends to learn it on your parts.

The shop behind this PEEK guide, and how to verify it before quoting

Backing this guide is a 6,800 m² plant at No. 8, Shuibian Songyuan Road, Hengli Town, Dongguan, Guangdong, China 523470, running 100+ CNC machines — Mazak VARIAXIS I-600 and INTEGREX I-250H S, TSUGAMI B0206-III/B0205-III, STAR SR-32JII / SR-32J Type N, Citizen Cincom A20-3F7 — plus 3-, 4- and 5-axis milling and turning, 5+ wire EDM and a Hexagon CMM bench with 20+ gauges.

Milling holds ±0.003 mm, turning ±0.002 mm, and grinding or wire EDM ±0.002 mm, all checked on a Hexagon CMM with the 10:1 gauge rule applied to every feature. Capability: Ppk ≥ 1.67 initial and Cpk ≥ 1.33 in production on key characteristics. Certified to ISO 9001:2015 (116024/A/0001/UK/En), IATF 16949:2016 (131941/A/0001/SM/En, design clause 8.3 excluded, openly disclosed) and ISO 14001:2015 (116024/B/0001/UK/En), held by Dongguan Zhuohang Ltd, USCC 91441900MA4UWT6X39, established 2005. Customers across Austria, Belgium, the Czech Republic, Denmark, France, Germany, Greece, Hungary, Ireland, Italy, the Netherlands, Spain, Sweden and the United Kingdom in Europe; Brazil, Canada, Mexico and the United States in the Americas; China, Israel, Japan, Singapore and Sri Lanka in Asia; Australia and New Zealand in Oceania; and South Africa in Africa are supplied from China, worldwide. Contact Felipe Iglesias at [email protected] or +86 13126536955 to begin the quote, and ask for the certificate numbers, the machine list and a past CMM report together.

PEEK machining — your next steps before the RFQ

your move on PEEK is to send the drawing with the service temperature, the tolerance band, and the anneal expectation stated, and to ask the shop to propose a PEEK-realistic band, an anneal cycle, and a measurement condition in the quote. A shop that proposes all three has run PEEK; a shop that quotes the finished size alone has skipped the three decisions that decide whether the part passes. The facility behind this guide runs PEEK on 100+ CNC machines including Swiss-type turning at ±0.002 mm and 3/4/5-axis milling at ±0.003 mm, with Hexagon CMM verification in a temperature-controlled inspection environment, and Ppk ≥ 1.67 initial on key characteristics and Cpk ≥ 1.33 in production. The anneal plan, the tool geometry, and the measurement condition are part of the quote, not afterthoughts. Send the drawing and the service environment to Felipe Iglesias at [email protected] or +86 13126536955, and ask for the anneal cycle and the tooling plan alongside the tolerance evidence. Under ISO 9001:2015 (116024/A/0001/UK/En), IATF 16949:2016 (131941/A/0001/SM/En, design clause 8.3 excluded), and ISO 14001:2015 (116024/B/0001/UK/En), the PEEK process is documented end to end.

PEEK — your checklist before sending the RFQ

Before sending a PEEK RFQ, you should confirm five items: the grade (PEEK vs PEKK vs PEI), the service temperature, the tolerance band with the understanding that thermal expansion applies, the anneal expectation, and the measurement condition. A quote that addresses all five is a quote from a shop that has run PEEK; a quote that addresses only the finished size is a quote that will drift. The facility behind this guide addresses all five on the first exchange. Send to [email protected] or +86 13126536955.

What this shop actually runs

Capability evidence should come as specifics, not slogans. Behind this guide is a 6,800 m2 plant in Dongguan, China running 100+ CNC machines with 100+ staff. The machine list by category:

• 5-axis machining centres (10+) - Mazak VARIAXIS I-600 (510/910/510 mm travel, 12,000 rpm, 22 kW, 71.6 N·m, 30-tool BT40) and Mazak INTEGREX I-250H S (B-axis 0.0001°, 24 kW, 124 N·m, 38-tool HSK-A63). Made for compound-angle parts, single-setup multi-face prismatic work, and aerospace fittings where datum transfer loss is unacceptable.
• 3-axis / 4-axis machining centres (50+) - Brother SPEEDIO S500Z2N / S700Z2N (10,000 rpm, 14/21-tool ATC, 0.7 s tool-to-tool, Z-axis 2.2 G) and Mazak VCE-430A L / VCE-570C L (10,000 rpm, 118 N·m, 24-tool ATC). Made for prismatic parts, plates, brackets, housings.
• Swiss-type turning centres (10+) - Citizen Cincom A20-3F7 (Φ20 mm, 10,000 rpm), TSUGAMI B0206-III / B0205-III (Φ20 mm, 0.1 µm), STAR SR-32JII / SR-32J Type N (Φ32 mm, 8,000 rpm). Made for long, slender rotational parts at ±0.002 mm.
• CNC turning centres (20+) - HEADMAN T70M/1250 (720 mm swing, 117 mm bore, 3,000 rpm, BMT75 12-station turret). Made for shafts, bushings, flanges up to ±0.002 mm.
• Wire EDM (5+) - Sodick AQ535L (550/350/300 mm travel, ±20° taper, 800 kg workpiece). Made for hardened tool steel, internal splines, sharp internal corners that milling cannot reach.
• Inspection: Hexagon CMM + 20+ gauges - Hexagon CMM for coordinate measurement, plus vision system, profilometer, hardness tester, coating thickness gauge, XRF for material verification. The 10:1 rule (gauge 10x more accurate than the band) is applied to every feature.
• Machine highlights - VARIAXIS I-600: one-setup multi-face 5-axis + MAZA-CHECK auto-calibration; INTEGREX I-250H S: DONE-IN-ONE mill-turn, B-axis 0.0001° + Ai thermal shield; SPEEDIO S500Z2N / S700Z2N: Z-axis 2.2 G + 0.7 s ATC; Swiss-type: guide-bush switchable + 0.1 µm resolution.

Tolerance: ±0.003 mm CNC milling / ±0.002 mm CNC turning / ±0.002 mm grinding and wire EDM. Capability: Ppk >= 1.67 initial on key characteristics, Cpk >= 1.33 ongoing.

Certificates: ISO 9001:2015 (116024/A/0001/UK/En), IATF 16949:2016 (131941/A/0001/SM/En, with design clause 8.3 excluded, stated openly) and ISO 14001:2015 (116024/B/0001/UK/En), issued to Dongguan Zhuohang Ltd, registration 91441900MA4UWT6X39, founded 2005.

Where we ship: Austria, Belgium, the Czech Republic, Denmark, France, Germany, Greece, Hungary, Ireland, Italy, the Netherlands, Spain, Sweden and the United Kingdom in Europe; Brazil, Canada, Mexico and the United States in the Americas; China, Israel, Japan, Singapore and Sri Lanka in Asia; Australia and New Zealand in Oceania; and South Africa in Africa — plus other countries and regions worldwide, shipped from our base in Dongguan, China.

Contact: Felipe Iglesias, [email protected], +86 13126536955.

Frequently Asked Questions

Standards referenced on this page

• ASTM B211/B211M-19 — Standard Specification for Aluminum-Alloy Rolled or Cold Finished Bar, Rod, and Wire
• ASTM A582/A582M-12 — Standard Specification for Free-Machining Stainless Steel Bars
• ISO 9001 — Quality management systems — Requirements