🧪 PEEK
PEEK Machining in Oshkosh, WI — Unfilled, Glass-Filled, and Carbon-Filled Grades
PEEK (polyether ether ketone) is not a material you specify because it is cheap — it is one of the most expensive engineering polymers available, running $40–$80 per pound for unfilled rod depending on grade and diameter. You specify it because nothing else survives 260°C continuous service temperature, chemical exposure to hydraulic fluid and jet fuel, and 50,000 PSI compressive strength simultaneously while being 60 percent lighter than aluminum. Oshkosh-area defense and equipment engineers reach for PEEK when a metal component is too heavy, too corrosion-prone, or electrically conductive in a way that causes problems — and when lower-cost polymers like nylon or Delrin have already failed in the application.
ISO 9001AS9100ITAR
Unfilled PEEK: Properties and Applications in Defense Assemblies
Unfilled PEEK (neat PEEK, natural grade) is the baseline against which all filled grades are measured. It provides continuous service temperature of 260°C (500°F), tensile strength of 14,000 PSI, compressive strength of 18,000 PSI, flexural modulus of 600,000 PSI, and chemical resistance to virtually all organic solvents, hydraulic fluids, fuels, and steam. Its dielectric strength is approximately 480 V/mil, making it an excellent electrical insulator — a property that disappears when conductive fillers are added.
In Oshkosh defense programs, unfilled PEEK appears in bearing cages, seal retainers, bushings in hydraulic systems, standoffs and spacers in high-voltage electronic assemblies, and wear pads in vehicle mechanical linkages. The material's FDA compliance (unfilled PEEK meets FDA 21 CFR requirements) is irrelevant to defense, but its USP Class VI biocompatibility is sometimes leveraged in medical device work that overlaps with the Fox Valley precision machining community.
Machining unfilled PEEK requires carbide tooling with sharp cutting edges, positive rake angles, and consistent coolant application to prevent thermal buildup. The material's glass transition temperature is 143°C — well above what normal machining generates, but localized heat from dull tooling or interrupted chip evacuation can soften the polymer and cause dimensional instability. Recommended surface speeds: 800–1,200 SFM for turning, 500–800 SFM for milling, with through-spindle or flood coolant to maintain chip temperature below 100°C. Tolerances of ±0.001 inch are routinely achievable on well-maintained CNC equipment with proper workholding.
Glass-Filled PEEK: Stiffness for Structural Load-Bearing Components
Glass-filled PEEK (typically 30% short glass fiber by weight, designated GF30 or 30% GF) trades some of unfilled PEEK's chemical resistance and electrical insulation for significantly higher stiffness and reduced creep. Tensile strength increases to approximately 21,000 PSI, flexural modulus approximately doubles to 1,200,000 PSI, and the coefficient of thermal expansion (CTE) drops closer to aluminum — reducing differential thermal expansion issues when PEEK components mount against metal structures.
For Oshkosh-area heavy-equipment programs, glass-filled PEEK is the correct grade for structural brackets, motor housings in power-dense drive systems, fluid manifold bodies in chemical environments, and bearing housings where long-term creep under sustained load would cause unfilled PEEK to drift out of tolerance. The glass fibers are abrasive — tool wear rates with GF30 PEEK run 3–5 times higher than with unfilled PEEK. Carbide tooling with PCD (polycrystalline diamond) edge preparation is recommended for production runs above 50 pieces; otherwise plan for insert changes every 20–30 parts on tight-tolerance features.
GF30 PEEK is not appropriate when electrical insulation is required — the glass fiber content slightly reduces dielectric strength, and more importantly, glass-fiber composite surfaces are microscopically porous in a way that can trap moisture and degrade insulation resistance over time. For electronics enclosures requiring both stiffness and insulation, unfilled PEEK remains the correct choice.
Carbon-Filled PEEK: Bearing, Wear, and Tribological Applications
Carbon-filled PEEK (CF30 or CF15 — 15–30% carbon fiber or carbon particles) is the grade specified when wear resistance, low friction, and maximum stiffness are the primary requirements. The carbon filler serves as a solid lubricant — reducing the coefficient of friction from unfilled PEEK's 0.35–0.45 against steel to 0.10–0.20 for carbon-filled grades. Flexural modulus for CF30 reaches 2,000,000+ PSI, approaching the lower range of aluminum. Compressive strength exceeds 25,000 PSI.
In Oshkosh defense and equipment programs, carbon-filled PEEK appears in dry-running bearing rings, bushings in articulating joints, piston rings and seal rings in hydraulic equipment where oil-free operation is required, and wear strips in guide systems. Its electrical conductivity (carbon filler makes the material semi-conductive to slightly conductive) is a design consideration — CF PEEK will not build static charge, which is useful in electronics assembly environments but rules it out for electrical isolation applications.
Machining CF30 PEEK requires the same carbide tooling discipline as GF30 but with additional attention to edge sharpness — carbon fiber composites produce fraying and delamination at machined edges when tools are dull, and that fraying shows up as dimensional non-conformance on bore diameters and chamfers. PCD tooling extends life significantly on production runs. Surface finish achievable: 32 Ra or better with sharp carbide, 16 Ra or better with PCD. One handling note: carbon fiber PEEK dust is electrically conductive — shop ventilation and cleanup procedures should prevent chip and dust accumulation on electrical panels.
Grade Selection and Regional Sourcing for PEEK in the Fox Valley
Selecting the right PEEK grade for an Oshkosh defense or equipment program follows a logical decision tree: start with unfilled PEEK if electrical insulation, food/drug compliance, or maximum chemical resistance is required; upgrade to GF30 if creep under sustained load or stiffness matching aluminum is the driver; specify CF30 if dry-running wear or friction reduction is the primary need. Combinations (glass-and-carbon-filled PEEK, PTFE-filled PEEK for ultra-low friction) are available from specialty compounders but carry 6–10 week lead times.
Material availability in the Fox Valley: PEEK rod and plate in standard diameters (0.25–4 inch rod, 0.25–2 inch plate) is stocked by industrial plastics distributors in Milwaukee, Appleton, and Green Bay — delivery to Oshkosh typically 1–3 business days for stock grades. Large cross-sections (rod above 4 inch diameter, thick plate) are less commonly stocked and may require 3–6 weeks from specialty polymer distributors. Victrex, Solvay (KetaSpire), and RTP Company are the primary material producers; shops should confirm the material brand on the cert, as commodity PEEK from offshore sources has been found to contain recycled or substandard resin that does not meet published mechanical property specifications.
Frequently Asked Questions
PEEK makes economic sense when one or more of the following conditions apply: the component operates continuously above 150°C where most engineering plastics soften, the application requires chemical resistance to hydraulic fluids, fuels, solvents, and steam simultaneously, the part needs to be electrically non-conductive in an environment where metal would cause ground faults or galvanic corrosion, or weight reduction from aluminum is still not enough and the next step down is a polymer that must survive the thermal and chemical environment. The raw material cost of PEEK ($40–$80/lb for rod) is 30–100 times higher than aluminum and 10–20 times higher than nylon, so the material cost of a machined PEEK part is substantially higher than its aluminum equivalent. The economic justification comes from system-level benefits: a PEEK bushing in a hydraulic actuator that operates at 200°C might last 50,000 cycles dry-running while a nylon equivalent lasts 5,000 cycles and requires maintenance shutdown. For Oshkosh defense programs with high availability requirements, that maintenance elimination often justifies the premium. Start the evaluation by identifying what the current material failure mode is — if it is thermal softening, chemical attack, or creep, PEEK addresses all three.
Experienced CNC shops machining PEEK in the Fox Valley region routinely hold tolerances of ±0.001 inch on bore diameters and ±0.002 inch on external features for production quantities. First-article tolerances of ±0.0005 inch are achievable on critical fits when the shop has temperature-controlled environment (68°F ±2°F) and uses carbide tooling with consistent tool-life management. The key variables that degrade PEEK dimensional accuracy are: thermal expansion during machining (PEEK CTE is 2.6 x 10⁻⁵ /°C — nearly 4 times aluminum — so heat from cutting causes significant workpiece growth), residual stress in stock material (PEEK rod can have molded-in stress that releases when machined, causing bowing or diameter shift in thin-walled parts), and moisture absorption (PEEK absorbs 0.1–0.5% moisture by weight, causing slight dimensional growth in humid environments — dry the stock before precision machining). For medical-grade or defense programs requiring FAI with all dimensions reported, ask the supplier about their temperature stabilization procedure before measurement — parts should sit at ambient temperature for at least 4 hours after final machining before CMM inspection.
PEEK is compatible with all common sterilization methods including autoclave steam sterilization at 134°C (it handles this repeatedly with no degradation), gamma irradiation at standard 25–50 kGy doses, ethylene oxide (EtO) gas, and electron beam sterilization. This is one of the reasons PEEK has become the dominant engineering polymer in implantable medical devices and surgical instrument components — and while that is not the primary driver in Oshkosh's heavy-equipment and defense market, some Fox Valley precision machining shops serve both sectors and understand PEEK's sterilization compatibility. More relevant to defense programs: PEEK's resistance to decontamination chemicals (bleach solutions, hydrogen peroxide vapor, quaternary ammonium compounds) used in CBRN (chemical-biological-radiological-nuclear) scenarios means components do not degrade during field decontamination procedures that would attack nylon, acetal, or most other engineering polymers. For vehicle interior components, electronic equipment housings, and NBC filter assemblies where decontamination is a service requirement, PEEK's chemical resistance across that spectrum is a meaningful functional advantage over lower-cost alternatives.
Victrex (PEEK 150G, 450G, 90G) and KetaSpire (Solvay) are the two dominant commercial PEEK polymer producers, and their base resins are compositionally equivalent — both are polyether ether ketone produced by nucleophilic aromatic substitution polymerization. The grade numbers in Victrex's system (90G, 150G, 450G) refer to viscosity class, which correlates to molecular weight and affects melt flow for injection molding but has minimal effect on the mechanical properties of compression-molded or extruded rod and plate used for machining. For machined components, the brand of PEEK used in the rod or plate stock has little practical effect on dimensional accuracy, strength, or chemical resistance if both are unfilled CP (compression-polymer) grade from reputable producers. The risk is with commodity PEEK rod from offshore compounders that blend virgin and regrind or use undisclosed filler systems — this material sometimes passes casual inspection but fails under chemical or thermal stress. For defense and AS9100 programs, specify on your drawing or purchase order: 'Material: PEEK per ASTM D6262, virgin resin only, no regrind, MTR required with manufacturer lot number.' That language allows any qualified brand while filtering out substandard material.
PEEK is relatively stable compared to moisture-sensitive polymers like nylon, but some precautions improve dimensional consistency for precision assemblies. Finished PEEK parts should be stored in sealed polyethylene bags with desiccant at room temperature away from UV light sources — not because PEEK absorbs significant moisture (it absorbs only 0.1–0.5% by weight at saturation, far less than nylon's 2–8%), but because temperature cycling in an unconditioned storage area can cause cumulative dimensional variation in tight-tolerance parts. Avoid storage near heat sources or on concrete floors in unheated facilities during Wisconsin winters, where floor temperatures can drop significantly and cause thermal contraction that shifts bore dimensions by 0.001–0.002 inch. For assembly involving metal mating parts (PEEK bushings pressed into steel housings, for example), account for differential thermal expansion: PEEK's CTE is approximately 2.6 x 10⁻⁵ /°C versus steel's 1.2 x 10⁻⁵ /°C — at operating temperature swings of 150°C, a 2-inch PEEK bore will grow roughly 0.008 inch more than the steel housing. That differential must be accommodated in the press-fit interference or the retained bushing will loosen in service. Defense assembly engineers should confirm thermal design margins with the design engineer before finalizing press-fit specifications on PEEK components.
Last updated: July 2026
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