POM vs PEEK for CNC Machining: Which Plastic Fits Your Part?

Both polymers can be machined from rod or plate, but they answer different design needs. POM is often considered for guides, sliding components, bushings and machine parts operating in relatively ordinary conditions. PEEK deserves evaluation when a component faces more demanding temperature or chemical exposure. A white or beige stock color does not establish material identity: pigment, filler, stock process and grade vary. Start a material decision with the actual operating temperature, load, mating surface, fluid exposure and intended service life. The cheapest blank is not automatically the lowest-cost functional part, and a premium polymer does not automatically improve an application that does not need its properties.

PEEK's major advantage is retention of useful properties at temperatures beyond those of many common engineering plastics. Ensinger describes long-term service temperatures of roughly 250–260 °C for certain PEEK grades, but this is not a blanket guarantee for every loaded component. A POM-C datasheet from the same supplier lists around 100 °C for long-term service. Read any number together with time under load, stress, stock form, environment and the design safety margin. Chemical compatibility also needs a defined fluid, concentration, temperature and exposure time. Neither 'chemical resistant' nor 'heat resistant' is a complete specification.

A sharp tool and dependable chip evacuation help limit local heat, burrs and surface damage. Plastic can deflect under a fixture: after unclamping, a thin wall may recover and read differently from its clamped condition. Thin sections or large pockets may benefit from staged roughing, a planned finishing allowance and time to stabilize before final inspection. For expensive PEEK stock, nesting, blank selection and risk of scrap deserve attention during quotation rather than after programming. Feed and speed are selected for the actual grade, geometry, cutter, machine and stock condition; there is no universal recipe that fits both materials.

Temperature and residual stress affect plastic dimensions, so agree on inspection conditions before debating a few hundredths of a millimeter. Inspect critical features after the part has stabilized under the agreed procedure. Support the part and choose measurement force so a probe does not indent a surface or bend a wall. For pin holes, plastic threads, sliding faces and flatness, specify datum features and the inspection method. A CMM result or a gauge result depends on how the part is supported. Requiring a very tight tolerance everywhere, including non-functional surfaces, may raise machining and inspection cost without improving assembly performance.

For an ordinary guide bushing, begin with load, sliding speed, lubrication and fit requirements before evaluating POM. For a component near heat or exposed repeatedly to demanding chemicals, evaluate PEEK with the precise grade datasheet and, where justified, testing. A filled POM or PEEK can behave differently from its unfilled base polymer. The polymer family name alone is insufficient when wear behavior, electrical properties or traceability are critical. The designer approves a material change; the machinist can identify process and dimensional risks.

Provide a revision-controlled 2D drawing, a matching 3D model when available, and a full material designation. State whether you need POM-C, POM-H, unfilled PEEK or a filled grade. If the grade is open, describe temperature, fluid and load so the engineering discussion starts with the application. Add prototype and production quantities, who supplies the blank, critical fits, burr requirements, required material documents, target delivery and inspection scope. VietTech reviews CNC milling or turning and suitable inspection against each drawing; any unusual requirement must be confirmed in the quotation rather than assumed to apply to all parts.

• Exact grade and stock form
• Drawing revision and functional tolerances
• Service condition and documents
• Quantity, timing and inspection scope