PEEK Machining and Molding: Grades, Properties, Annealing, Tolerances and Inserts

PEEK can be CNC machined from plate, rod, bar, sheet, tube or other stock, and it can also be injection molded or extruded from PEEK resin. The engineering decision is not simply whether to use PEEK material. You need the correct PEEK grade, stock or molding form, process route, tolerance strategy and inspection condition. Unfilled PEEK, glass filled PEEK, carbon filled PEEK and bearing grade PEEK can share the same polymer name while behaving differently in machining, molding and service. This guide connects PEEK properties to manufacturing decisions, then shows where ISO 23153, ASTM D8033 and ASTM D6262 help, and where they stop.

1. What Is PEEK Material, and Which Properties Matter?

Polyetheretherketone, also written polyether ether ketone, is a semi-crystalline high performance polymer and engineering thermoplastic. PEEK plastic is used when a design needs a combination of heat resistance, chemical resistance, wear performance, stiffness, electrical behavior or dimensional stability that lower-cost plastics may not provide. The useful question for manufacturing is not only what is PEEK material, but which PEEK material properties describe the exact grade and product form you will buy.

For the common question “what is PEEK plastic?”, it is a PEEK polymer in the PAEK family, used as a high performance plastic and high temperature plastic when ordinary engineering plastics do not meet the combined service requirements.

Start with the grade-specific data rather than a generic materials chart. EPOC CRAFTER’s PEEK material properties reference is most useful when it is read with the supplier PEEK material data sheet, test method and product form.

Property keyword	Why an engineer checks it	Decision boundary
PEEK density	Mass, inertia and part-weight calculations	Use the exact grade. Filled PEEK can have a different density from unfilled PEEK.
PEEK glass transition temperature	Thermal transition and stiffness change	Do not turn Tg into a finished-part service limit.
PEEK melting point	Molding and thermal-processing context	Use the test method and grade. It is not a machining temperature limit.
PEEK coefficient of thermal expansion	Tolerance change with temperature	For reinforced PEEK, direction can matter.
PEEK tensile strength and modulus	Load and stiffness screening	Standard specimen values are not finished CNC part guarantees.
PEEK creep	Sustained load, clamping and threaded interfaces	Time, stress and temperature must be considered together.
PEEK wear resistance and PEEK friction coefficient	Bearings, gears, seals and sliding parts	Use the actual wear or bearing grade and mating condition.
PEEK chemical resistance	Fluid, cleaning and process exposure	Confirm the actual chemical, concentration, temperature and time.
PEEK moisture absorption and PEEK electrical properties	Electrical isolation and dimensional environment	Check grade-specific data and service condition.
PEEK hardness	Surface and contact screening	Hardness does not replace wear, creep or interface testing.

Table note: the table identifies what to check. It intentionally avoids universal property numbers because PEEK grades, specimen preparation and test directions differ.

A grade review normally separates PEEK mechanical properties from PEEK thermal properties. Check PEEK continuous use temperature, PEEK heat resistance and PEEK thermal expansion only with the stated grade and test condition; the same rule applies to density, tensile data, creep, wear and chemical exposure.

ISO 23153-1:2020 helps classify PEEK moulding and extrusion materials using melt viscosity or melt volume-flow rate, tensile modulus, tensile strength, processing information, fillers and reinforcing materials. Its codes represent classification ranges, not exact batch values. The standard also warns that materials with the same designation can still differ because processing conditions and morphology can differ. That is why a PEEK datasheet is a material reference, not a finished-part acceptance specification.

2. PEEK Grades and Stock Forms

PEEK grades should be selected before the machining or molding route is locked. The most common engineering choices include unfilled PEEK, reinforced PEEK such as 30% glass filled PEEK or 30% carbon filled PEEK, and wear-oriented or bearing grade PEEK. Medical grade PEEK and implant grade PEEK also need separate qualification because ordinary PEEK medical use does not automatically establish implant suitability.

PEEK material grades are not interchangeable labels. Carbon fiber reinforced PEEK, glass reinforced PEEK and unfilled material can require different machining, inspection and molding decisions.

PEEK grade family	Verified selection rationale	Manufacturing review
Unfilled PEEK	Good machinability; used when filler-free chemistry, electrical isolation or general precision machining matters	Stock stress, creep and dimensional movement still need control.
Glass filled PEEK / GF30	Higher rigidity, creep strength and dimensional stability than unfilled material	Glass reinforcement can be abrasive; flow or fibre direction can affect behavior.
Carbon filled PEEK / CF30	Higher rigidity and creep strength; carbon fibre reinforced PEEK is used where stiffness and dimensional response drive selection	Tool wear, surface behavior and anisotropy need review.
Bearing grade PEEK	Modified for sliding, friction or wear service	Do not assume the filler system is equivalent to unfilled, GF30 or CF30 material.

Table source check: ISO 23153-1 and ASTM D8033 distinguish reinforcement and filler systems. Ensinger’s official TECAPEEK GF30 page describes increased rigidity, creep strength and dimensional stability; TECAPEEK CF30 describes increased rigidity and creep strength; TECAPEEK PVX is a bearing and sliding grade with a modified filler system. These are supplier-grade examples, not universal guarantees for every PEEK supplier.

Stock form matters just as much as grade. PEEK rod, PEEK plastic rod, PEEK bar, PEEK sheet, PEEK plastic sheet, PEEK plate, PEEK billet, PEEK tube and PEEK tubing are machining inputs. PEEK resin, PEEK pellets and PEEK granules are typical PEEK extrusion, PEEK compression molding or injection-molding inputs. An extruded PEEK rod can carry a different processing history from a compression molded plate or an injection molded blank, so PEEK raw material should never be reduced to the polymer name alone.

3. PEEK CNC Machining or Injection Molding?

PEEK CNC machining and PEEK injection molding solve different production problems. CNC machining PEEK is usually easier to change during development because the geometry comes from toolpaths and fixtures. PEEK molding adds dedicated tooling, but it becomes more attractive when geometry is stable and production volume can justify the mold. Some PEEK components use both routes: molding creates the near-net shape, then PEEK precision machining establishes critical datums, bores or sealing faces.

PEEK machined parts and molded PEEK plastic parts can meet the same assembly need through different routes, so the drawing should identify which features must be produced or finished by machining.

Decision factor	PEEK CNC machining	PEEK injection molding	Engineering decision
Starting material	PEEK plate, rod, bar, tube or other stock	PEEK resin or pellets	Choose the route that matches the purchased material form.
Design changes	Program and fixture changes are usually easier	Tool changes may be required	CNC often fits prototypes and changing designs.
Low-volume parts	No dedicated mold required	Tooling can dominate the economics	Compare total program cost, not raw material price.
High-volume parts	Chip generation and cycle time remain	Molding can scale once process and tooling are stable	Volume alone is not enough if critical features still need machining.
Tight bores and datums	Can be created directly by milling, drilling, reaming or turning	May need secondary machining	Control the functional feature, not every dimension.
Dimensional risk	Stock stress, material removal and clamping	Flow, cooling, shrinkage and filler orientation	The dominant variation source changes with process route.

For machined parts, the published PEEK CNC machining capability should be used with the drawing, exact grade and inspection plan rather than as a blanket tolerance promise.

For molded parts, the PEEK rapid injection molding process is relevant when tooling, quantity, resin processing and secondary machining are part of the same decision.

4. How to Machine PEEK Without Losing Dimensional Control

PEEK machinability is generally good, but PEEK plastic machining can still fail dimensionally when the part is thin, heavily pocketed or clamped into shape. PEEK milling, drilling, reaming and thread milling should be planned around the part’s free-state geometry. Sharp tools, controlled chip evacuation and low-distortion workholding matter, but the larger issue is often how much material is removed and when the part is released from the fixture.

PEEK cutting conditions still need to match the operation. The same geometry may behave differently in unfilled stock and reinforced stock, and PEEK machining distortion or PEEK warpage should be checked in the free state rather than hidden by clamp load.

For unfilled PEEK, polished carbide tools with positive rake are a practical starting point. Filled PEEK changes the cutting problem because glass and carbon reinforcement can increase tool wear and introduce directional behavior. That is why machining PEEK GF30 or carbon fiber PEEK should not inherit the same tool-life assumptions as unfilled PEEK.

Heavy roughing should leave enough stock to restore datums after the part has moved. A staged route can include bulk roughing, release from the fixture, free-state inspection, a stability decision, datum restoration and finish machining. This is not a universal routing rule for every machined PEEK part. It becomes more useful as wall thickness falls, pockets deepen, material removal becomes asymmetric and PEEK machining tolerances tighten.

For feature-level geometry decisions, the PEEK machining DFM guidelines help separate function-critical walls, bores and datums from dimensions that do not need the same control.

5. PEEK Annealing, Residual Stress and a Shop-Floor Case

PEEK annealing is not automatically required before or after machining. There is no single PEEK annealing temperature or PEEK annealing process in ISO 23153-1, ISO 23153-2, ASTM D8033 or ASTM D6262 that applies to every CNC part. Annealing PEEK is a process decision tied to stock condition, geometry, material removal, dimensional movement and the required tolerance.

Questions about how to anneal PEEK should therefore start with the exact supplier grade, stock condition, section thickness and measured movement, not with a copied generic cycle.

ISO 23153-2 conditioning is for standardized test specimens, not a CNC stress-relief cycle. ASTM D6262 also includes a dimensional-stability thermal exposure, but that test condition is not a production annealing schedule. Confusing test conditioning with a machining heat-treatment recipe is one of the easiest ways to create an unsupported process rule.

The distinction between a standard test condition and a production heat-treatment decision is also explained in EPOC CRAFTER’s PEEK annealing and machining sequence reference, where the same evidence boundary is applied to machining sequence decisions.

5.1 EPOC CRAFTER Case: Dimensional Stability After Roughing

EPOC CRAFTER case PEEK-DS-2026-017 used virgin unfilled natural PEEK plate for a semiconductor metrology carrier. The extruded plate had been supplier stress-relieved before shipment. The starting stock was 160.02 x 120.04 x 18.03 mm with 0.09 mm initial flatness. The finished part was 148.00 x 108.00 x 12.00 mm with a 96.00 x 64.00 x 8.00 mm pocket, four 6.00 H7 locating bores, eight 4.50 mm through holes and four M5 x 0.8 threads.

Stage	Measured result	Why it matters
After first roughing and unclamping	0.16 mm center bow; 0.11 mm diagonal twist	Movement appeared before final dimensions were cut.
Process correction	Symmetric staged removal; lower clamp load; intermediate 200 C stress relief; datum A restored after heat treatment	The change addressed stress release and restraint, not only cutting speed.
After stress relief and 12 h stabilization	0.07 mm center bow; 0.04 mm twist; maximum free-state shift 0.05 mm	The part moved before finish machining, leaving recovery stock available.
Final inspection	Flatness 0.034 mm; maximum bore position 0.046 mm; perpendicularity 0.031 mm	Final geometry met the drawing after datum restoration.
72 h repeat check	Maximum overall change 0.012 mm; flatness change 0.006 mm	The repeat check targeted delayed dimensional movement.

The case result should not be generalized into a universal PEEK annealing cycle. It shows something narrower and more useful: on this geometry, PEEK residual stress, asymmetric removal and fixture recovery mattered more than simply slowing the final pass. The production lot that followed used the revised route; 12 parts passed first final inspection after one process-development part had required rework.

6. PEEK Machining Tolerances and Inspection

PEEK machining tolerances belong to the finished drawing and inspection plan. ASTM D6262-23 covers PAEK basic shapes such as sheet, plate, rod and tubular bar, including stock dimensions, workmanship and dimensional stability. Those stock requirements help with purchasing, raw-stock inspection and machining allowance. They do not become finished CNC tolerances automatically.

The case drawing required overall length and width at +/-0.05 mm, thickness at +/-0.03 mm, four locating bores at 6.000 to 6.012 mm, datum A flatness at 0.05 mm, bore position at diameter 0.08 mm to A|B|C, and B-to-A perpendicularity at 0.05 mm. Final inspection was performed at 20.1 C after stabilization, with the part free-state. The four finished bores measured 6.006, 6.007, 6.005 and 6.008 mm.

That does not mean every PEEK component can be quoted to the same limits. PEEK machining tolerance capability depends on feature type, part size, wall thickness, stock condition, grade, setup, thermal state, datum strategy and measurement method. PEEK dimensional stability should therefore be verified against the failure mode that matters: flatness, bore size, location, sealing, thread acceptance or another defined function.

The same principle applies to any controlled drawing. EPOC CRAFTER’s PEEK CNC drawing tolerance strategy explains how explicit size limits, GD&T and inspection temperature should be separated by feature function.

7. Threads, Holes and PEEK Inserts

PEEK inserts and directly machined threads should be selected from the joint load, assembly frequency, temperature, creep exposure and surrounding wall thickness. A machined thread may be enough for a lightly loaded interface that is assembled only a few times. A metal insert can be justified when repeated assembly, higher torque, wear or load concentration would make a polymer thread less robust.

The reviewed PEEK standards do not specify a universal heat-set insert temperature, press-fit interference, insertion force, thread pull-out value or minimum boss thickness. ASTM D6262 includes a machined-hole specimen in its dimensional-stability method, but that does not establish PEEK design rules for drill size, tapping, insert bores or thread engagement.

Interface	What the drawing or assembly specification should define
Machined thread	Thread designation, depth or engagement, position, gauge or acceptance method
Locating bore	Diameter tolerance, datum relationship, position and finish if functional
Clearance hole	Diameter and location matched to fastener and assembly
Insert bore	Geometry required by the selected insert supplier and installation process
Metal insert	Insert type, material, depth or flush condition, installation method, torque or pull-out requirement when needed
Press-fit feature	Fit target and validation method for the actual PEEK grade and geometry

8. PEEK Injection Molding: Drying, Processing Temperature and Shrinkage

PEEK injection moulding and PEEK moulding need grade-specific processing control. ISO 23153-2:2020 is useful because it standardizes specimen preparation for comparable PEEK properties. For those standardized specimens, the material is pre-dried to moisture not exceeding 0.05% by ISO 15512, then injection molded under defined conditions. That requirement does not mean every PEEK plate must be dried to the same level before CNC machining.

Can PEEK be injection molded? Yes, but the PEEK processing window must come from the selected grade, mold design and validated process rather than from a generic material label.

Processing item	Verified value	Scope
Pre-drying for ISO 23153-2 test specimens	Moisture <=0.05% by ISO 15512	Standardized specimen preparation only
PEEK processing temperature, melt	360 to 400 C	ISO 23153-2 standardized injection-molded specimens
PEEK molding temperature, mold	175 to 210 C	Standardized specimen condition; filled grades may need different conditions
Average injection velocity	100 +/-20 mm/s	Standardized specimen condition
Cooling time	25 +/-10 s	Standardized specimen condition
Total cycle time	60 +/-10 s	Standardized specimen condition

These values are not a universal production window for every commercial grade. PEEK processing must still follow the selected supplier grade, mold geometry and validated trial. PEEK shrinkage also needs direction and grade context. ISO 23153-2 distinguishes parallel and normal molding shrinkage and direction-dependent thermal expansion for reinforced materials, so a single shrinkage value is not enough for GF30 or CF30 design.

If the question is “what is the melting point of PEEK?”, use the exact grade datasheet and test method. PEEK melting point is useful for material characterization, but it does not by itself define PEEK processing temperature, PEEK molding temperature or a safe service limit.

A broader material-selection workflow is available in the PEEK injection molding material selection guide, which links resin properties to wall, gate, shrinkage and process decisions.

For geometry before tool release, the PEEK injection molding DFM design guide is the relevant next step for wall transitions, draft, ribs, gates and warpage review.

9. Where PEEK Makes Engineering Sense

What is PEEK used for? PEEK applications make sense when the part truly needs the combined thermal, chemical, wear, electrical or dimensional performance. Common PEEK components include PEEK bearings, PEEK gears, PEEK seals, PEEK implants made from separately qualified implant materials, electrical isolation parts, semiconductor fixtures, PEEK electronics hardware, PEEK medical devices, PEEK aerospace hardware and selected PEEK automotive components.

Material comparison should stay tied to the failure mode. PEEK vs PTFE is often a stiffness and creep question as much as a friction question. PEEK vs Ultem or PEEK vs PEI can turn on chemical exposure, wear and the need for a semi-crystalline rather than amorphous polymer. PEEK vs PPS can be a cost and performance trade. PEEK vs Delrin, PEEK vs acetal or PEEK vs POM often comes down to service temperature, chemical exposure and material cost. For PEEK vs aluminum, PEEK vs stainless steel, PEEK vs metal, PEEK vs nylon or PEEK vs polycarbonate, the right answer depends on structural load, electrical isolation, corrosion, weight, temperature and manufacturing route.

PEEK price is high enough that material over-specification matters. PEEK cost and PEEK material cost depend on grade, stock form, certification, machining scrap and inspection. A PEEK rod price or PEEK supplier quote should therefore be reviewed with machining yield and documentation, not as resin price alone. The useful procurement question is why is PEEK expensive for this part, and whether the service requirement actually justifies the upgrade.

For medical projects, the PEEK medical device manufacturing requirements provide the application context for traceability, sterilization, precision interfaces and regulated documentation.

10. How to Specify PEEK on a Drawing, RFQ or Purchase Order

A PEEK material specification should separate material classification, product form and finished-part acceptance. ISO 23153-1:2020 is a PEEK standard for designation and specification basis. ISO 23153-2:2020 covers standardized specimen preparation and property determination. ASTM D8033-22 classifies PEEK molding and extrusion materials. ASTM D6262-23 covers PAEK basic shapes used for later fabrication.

There is no single “PEEK ASTM” document that covers resin classification, stock shape, machining tolerance, inserts and finished-part acceptance at once. Each standard below controls a different layer.

Standard	Primary object	Useful procurement control	Do not use it for
ISO 23153-1:2020	PEEK moulding and extrusion material designation	Polymer identity, filler or reinforcement, processing information, MV/MVR class, tensile modulus class, tensile strength class, optional additional requirements	Does not define finished CNC tolerances, insert parameters or a universal annealing cycle.
ISO 23153-2:2020	Standardized PEEK specimen preparation and property testing	Drying, molding conditions, conditioning, property test framework	Does not define PEEK plate/rod tolerances or finished-part acceptance.
ASTM D8033-22	PEEK molding and extrusion material classification	Group, Class, Grade, reinforcement/filler, property cells and suffixes	Not a material-selection system and not a PEEK stock-shape dimensional specification.
ASTM D6262-23	PAEK basic shapes	Stock material, product form, dimensions, workmanship, dimensional stability and certification when ordered	Stock tolerance is not the finished PEEK machining tolerance.

ASTM D8033 also shows why a label such as ‘GF30 PEEK’ is incomplete for substitution. A full line callout can identify Group, Class, Grade, reinforcement and property cells, while suffixes add requirements not captured by the basic classification. ASTM D8033 is still not a material-selection system. ISO 23153-1 likewise states that matching designations do not automatically prove identical performance.

When buying CNC stock, add the downstream basic-shape requirement. A useful PEEK material certification package can include the exact commercial grade or classification, product form, lot traceability, CoC and any required test report. For PEEK sheet, PEEK plate, PEEK rod or PEEK tubing, incoming stock dimensions and condition affect machining allowance and fixturing. The finished drawing then controls final size, GD&T, surface finish, threads, inserts and inspection.

11.Frequently Asked Questions

Is PEEK machinable?

Yes. PEEK is machinable with conventional CNC milling, turning, drilling and reaming methods, but PEEK machinability depends on grade, stock form, wall thickness, material removal, workholding and inspection. Filled grades can increase tool wear, while tight PEEK machining tolerances may require staged roughing and free-state inspection.

Does PEEK need annealing before CNC machining?

Not every PEEK part needs annealing. A PEEK annealing review becomes more relevant for large or thin parts, heavy material removal, asymmetric geometry, tight flatness or elevated service temperature. There is no universal PEEK annealing temperature or cycle in the four standards reviewed here.

What tolerances can be achieved on CNC machined PEEK parts?

There is no single universal tolerance. The case in this article reached 0.034 mm flatness and 0.046 mm maximum bore position on one specific plate after staged roughing, stress relief, datum restoration and controlled inspection. Those are case results, not a general PEEK precision machining guarantee.

Which PEEK grade should be machined?

Choose the grade from the service requirement first. Unfilled PEEK, glass filled PEEK, carbon filled PEEK and bearing grade PEEK differ in stiffness, wear behavior, filler content, tool wear and dimensional response. Confirm the exact commercial grade before quoting.

Is it cheaper to use injection molding instead of CNC for PEEK?

It depends on quantity, tooling, geometry, stock utilization and secondary machining. CNC often fits prototypes and lower volumes because no dedicated mold is needed. Injection molding can reduce per-part processing at scale, but critical datums or bores may still need machining.

Can threaded inserts be used in PEEK?

Yes, but the insert geometry and installation process must be validated for the selected grade, boss geometry, service load and temperature. ISO 23153, ASTM D8033 and ASTM D6262 do not supply a universal heat-set temperature, press-fit interference or pull-out value.

PEEK RFQ and Drawing Checklist

RFQ item	What to define
Material	Exact PEEK grade; unfilled or reinforced status; filler type and content; approved supplier grade if required
Stock or resin	PEEK plate, rod, tube, pellets or molded blank; extrusion, compression molding or injection molding route
Function	Service temperature, chemical exposure, wear, electrical isolation, sustained load, cleanliness or sterilization
CNC machining	Critical datums, thin walls, deep pockets, precision bores, asymmetric removal, finish-stock strategy
Injection molding	Exact molding grade, supplier processing guidance, wall transitions, gate/flow direction, shrinkage and secondary machining
Tolerances	Critical dimensions, GD&T, surface finish, inspection temperature and free-state or restrained measurement condition
Threads and inserts	Thread depth, insert type, bore geometry, installation method and acceptance requirement
Documentation	ISO 23153 or ASTM D8033 classification where applicable, ASTM D6262 for applicable basic shapes, CoC, lot traceability, test reports
Substitution	Approved alternate grades or formal engineering approval process

A useful RFQ tells the supplier what PEEK material is required, which product form is being purchased, which finished features control function and what evidence is required to accept the part. That is more actionable than writing only ‘Material: PEEK.’