Guide
How should PEEK machining be specified for annealing, dimensional stability and cost?
PEEK machining is cutting finished parts from extruded or compression-molded polyetheretherketone rod, plate or tube, usually for parts that need heat, chemical or wear resistance beyond common plastics. For tight tolerances, specify stress-relieved stock, allow an intermediate anneal before the final cuts on heavily machined parts, measure at a controlled temperature, and expect cost to be driven mainly by material price, scrap risk and tool wear on filled grades.
By Saola Manufacturing engineering team · Published · Updated
For acetal parts the trade-offs are different, and the Delrin vs acetal guide covers them. This page is about PEEK only: what the polymer maker says about annealing and machining, and how to turn that into a drawing note and an RFQ.
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Why does a machined PEEK part move after machining?
Because stock shapes carry stresses from extrusion or molding, cutting releases and adds stresses, and PEEK has a low modulus and low thermal conductivity compared with metals. The part can warp when it is unclamped, or creep and shrink later in hot service.
Victrex, the PEEK producer, writes that machining and finishing can create stresses or release residual stresses, that annealing may be needed before machining or as an intermediate step, and that a second anneal is recommended before final machining when a large amount of material is removed. It adds that its materials have a relatively low modulus compared with metals and are easily warped or distorted by high clamping forces, so material should be removed evenly and symmetrically, and that heat builds up quickly because polymers conduct heat poorly (Victrex finishing guide, January 2022).
There is also a service effect. The same guide notes that parts exposed to high continuous service temperatures may post-crystallize or relax internal stresses and change dimension, and that annealing can prevent that. So a PEEK part that measures correctly at receiving can still drift if it was never annealed and then runs hot.
When should PEEK stock or parts be annealed?
Order stress-relieved stock as standard, add an intermediate anneal between roughing and finishing when a lot of material comes off or tolerances are tight, and add a final anneal when the part will run near its upper service temperature. Simple parts from good stock often need none.
Victrex states that for the majority of applications secondary annealing is not necessary, and lists the cases where it is: to raise crystallinity, remove thermal history, limit later dimensional change at high temperature, or remove stresses (Victrex, 2022). For dimensional stability in service the Victrex guide recommends a holding temperature at least 20 °C above the maximum service temperature, with the anneal done before the final machining step.
Published cycles differ between sources in temperatures and hold times, so this guide does not repeat them. Leave the cycle to the processor, or name the polymer maker's procedure on the drawing, and specify the result you need instead.
| Situation | Anneal step | Why |
|---|---|---|
| Simple turned part, moderate tolerances, stress-relieved stock | Usually none | Stock is already stress relieved; little material removed |
| Heavy material removal, thin walls or asymmetric pockets | Intermediate anneal after roughing, then finish | Releases stresses before the final dimensions are cut |
| Tight flatness or bore tolerance | Intermediate anneal, fixtured | Prevents warping when the part is unclamped |
| Part runs near its upper service temperature | Anneal above service temperature before final machining | Prevents shrinkage from post-crystallization in service |
| Brown amorphous skin on natural-color material | Query the stock; anneal for crystallinity if accepted | Victrex links this skin to low crystallinity from processing |
How do you hold tolerances when machining PEEK?
Use sharp carbide or diamond tooling, light even cuts from both sides, low clamping force and coolant to control heat, and measure at a controlled temperature after the part has settled. Tolerances that are routine on metal may need more process steps in PEEK.
Victrex recommends carbide, coated carbide or diamond-tipped tools, because other tool materials wear quickly on PEEK and especially on filled compounds, and notes that its materials are compatible with water-based and oil-based coolants; it also lists grinding for very tight tolerances, especially on filled grades, and lapping for flatness (Victrex, 2022).
From a buyer's side, three things help. Tolerance only the features that need it and leave the rest open. State the measurement temperature, because plastics expand far more than metals with temperature. And for glass- or carbon-filled grades, accept that properties differ with direction in the stock, so a part cut from plate may not behave like a molded part of the same shape; Victrex makes this point for thin-walled parts machined from fiber-reinforced shapes.
What drives the cost of a machined PEEK part?
Material is the largest driver: PEEK stock costs far more than acetal or nylon, and the chips are paid for too. After that come scrap risk, extra anneal steps, slower finishing and tool wear on filled grades.
Because the stock is expensive, a scrapped PEEK part costs much more than the same scrap in a commodity plastic, so suppliers protect themselves with extra roughing and stress-relief steps on tight parts. Filled grades wear tools faster, and finishing to tight flatness or bore tolerances may need grinding or lapping. Each anneal is a furnace cycle with fixturing and handling.
Typical ways to lower cost: size the part to standard rod or plate dimensions so little material is wasted; open tolerances that are not functional; specify unfilled PEEK unless the filler is needed for stiffness, creep or wear; and if volumes grow, ask whether a molded near-net blank would be cheaper than cutting from stock. The CNC cost drivers guide covers the general logic.
How should a PEEK part be called out on the drawing and RFQ?
Name the grade (unfilled, glass-filled, carbon-filled or bearing grade), the stock specification, any brand or equal, the annealing requirement as a result, and any regulatory or certificate need. Do not write only PEEK.
ASTM D6262-23 covers the requirements for PAEK materials and the dimensions, workmanship and properties of extruded, compression-molded and injection-molded PAEK sheet, plate, rod and tubular bar (ASTM D6262-23 listing), which makes it a useful neutral stock callout. A generic note to adapt:
MATERIAL: PEEK, UNFILLED, NATURAL. STOCK SHAPE PER ASTM D6262, STRESS RELIEVED. [BRAND/GRADE] OR APPROVED EQUAL. ANNEAL AFTER ROUGH MACHINING PER MATERIAL SUPPLIER PROCEDURE. DIMENSIONS VERIFIED AT [TEMPERATURE] AFTER STABILIZING. MATERIAL CERTIFICATE REQUIRED.
If the part goes into a medical, food-contact or semiconductor application, say which regulatory or cleanliness requirement applies, because that limits which stock and which processor can be used. The RFQ preparation guide lists the rest of the package.
Can Saola machine PEEK parts?
Plastics machining is not confirmed at the lead plant, so whether a PEEK part can be made, and where, is decided at drawing review before any quote. Do not assume it from this guide.
The lead plant's CNC turning and CNC milling pages describe metal parts: steel, aluminum and silicon bronze bar on the turning side and mostly second operations on castings on the milling side. A PEEK drawing is reviewed for stock sourcing, annealing and inspection before a decision is given.
Send the drawing with the grade, stock form and annealing requirement written out, and say whether another engineering plastic or a metal would be acceptable.
Frequently asked
Does PEEK absorb water like nylon?
Far less. Victrex describes PEEK as having low moisture absorption and not hydrolyzing in water or steam, which is one reason it holds dimensions better than nylon in wet service.
Is annealed PEEK stronger?
Annealing to higher crystallinity raises some properties, such as strength, stiffness and chemical resistance, but Victrex notes that very high annealing temperatures can sharply reduce ductility in unfilled grades and can yellow the surface.
Can PEEK be machined dry?
Yes for many operations; Victrex lists no coolant or water- or oil-based coolant for turning. Coolant helps control heat on longer cuts and tighter tolerances.
Why did my PEEK part warp after it was unclamped?
Usually released stress from heavy or one-sided material removal, or clamping distortion. An intermediate anneal and symmetric, light finishing cuts are the usual fixes.
Is a machined PEEK part the same as a molded one?
Not always. Victrex notes that crystallinity, thermal history and fiber orientation can make the properties of a part machined from stock differ from a seemingly identical molded part, especially for thin walls in fiber-reinforced grades.
Sources
- Finishing guide for Victrex materials: machining, annealing, joining, Victrex plc (PEEK producer), January 2022
- ASTM D6262-23, Standard Specification for Extruded, Compression Molded, and Injection Molded Basic Shapes of Poly(aryl ether ketone) (PAEK) (scope), ASTM International via NSAI standards store, 2023