The short answer
**POM (acetal)** and **PEEK** are both CNC-friendly engineering plastics for functional prototypes, but they sit in different cost and performance brackets. POM is the everyday choice for low-friction jigs, gears, and insulating fixtures. PEEK is the high-temp / chemical / load narrative when POM’s limits show up—and the RFQ should say so, because **rates.v1.1** estimate logic prices stock and time differently than commodity plastics.
**Example part** wording only—no fabricated customer stories.
Buyer property sketch (confirm against your datasheet)
- **POM:** good machinability, low friction, decent stiffness for plastics, moisture uptake lower than nylon in many grades; watch creep and continuous temperature limits
- **PEEK:** higher continuous temperature capability, chemical resistance narrative, higher stock cost; still machinable but treat feeds/speeds and chip control as “premium plastic,” not acrylic hobby stock
- Neither replaces metal when heat + load + thread cycling demand aluminum or steel
Related reading: [engineering plastics PEEK/POM/nylon](https://3dwk.com/resources/choosing-engineering-plastics-peek-pom-nylon), [PA66 vs aluminum CNC prototypes](https://3dwk.com/resources/pa66-vs-aluminum-cnc-prototypes), [materials](https://3dwk.com/materials.php).
rates.v1.1 planning hooks (estimates)
Displayed planning rates emphasize several CNC materials; PA66 bar ~$5/kg with time coefficient ×0.8 is the nearby commodity plastic benchmark on the authorized card. POM and PEEK should be selected explicitly in the quote UI when offered—do not assume PA66 numbers equal POM or PEEK. Premium stocks (PEEK especially) raise material line items; thin walls and fine mills still drive time. Hot-alloy / CoCr auto-manual thresholds do not apply to these plastics the same way, but incomplete geometry can still yield **needs_manual**.
Always trust the live band on [quote-new.php](https://3dwk.com/quote-new.php) over blog arithmetic.
When POM is enough
Functional prototypes that check motion, snap fits (carefully), wear strips against soft counterparts, electrical insulation at modest temperature, or fixture nests often land on POM. Cosmetics are secondary; stress whitening and gate-like machine marks are acceptable if labeled prototype. If production intent is injection-molded acetal, say “CNC POM standing in for molded acetal—**Example part**.”
When PEEK earns its keep
Continuous elevated temperature, aggressive chemicals, or load cases where POM softens or creeps push PEEK (or filled PEEK grades when your drawing allows). Do not specify PEEK only because it “sounds aerospace.” Over-specifying PEEK on a room-temperature alignment comb burns budget without teaching new physics.
Illustration 1 is a decision matrix for an **Example part** prototype: temperature, chemicals, friction, cost sensitivity → POM vs PEEK.
CNC DFM notes shared by both
- Avoid knife-edge walls; plastics deflect under clamp and cutter load
- Prefer generous internal radii; sharp internal corners chatter
- Thread strategy: consider inserts for reused fasteners; note if self-tapping screws are the real assembly method
- Tolerance: plastics move with temperature and moisture—do not blanket ±0.02 mm like steel without a functional reason ([GD&T basics](https://3dwk.com/resources/gdt-basics-for-buyers))
- Finishes: most “anodize” notes do not apply—strip metal finish callouts from plastic RFQs
Quote packaging tips
State grade (e.g. POM-C vs POM-H; unfilled vs glass-filled PEEK) when it matters for stiffness. Qty breaks still help. If you need both a POM soft jaw and a PEEK high-temp clip, upload as separate lines so parse and material rates stay clean ([CNC cost drivers](https://3dwk.com/resources/cnc-machining-cost-drivers-buyer-guide)).
Illustration 2 shows RFQ wording for **Example part** POM vs PEEK intent notes next to the upload CTA path.
Example part walkthrough
**Example part:** sliding carrier, 80×40×12 mm, low friction vs aluminum rail, room temperature → POM CNC is the usual planning path. Same envelope in a 200 °C continuous airstream near solvents → PEEK conversation. Upload either path on [quote-new.php](https://3dwk.com/quote-new.php); label trade studies clearly.
What to do next
Pick the polymer that matches the property you need to learn, strip metal finishes from the drawing, and request the range via [CNC service](https://3dwk.com/cnc-machining-service.php) upload. Compare to aluminum only when stiffness or threads demand it ([6061 vs 7075](https://3dwk.com/resources/6061-vs-7075-aluminum-for-machined-parts)).
Common questions
Is POM always cheaper than PEEK online?
Stock cost usually yes; geometry can dominate. Compare live estimates rather than assuming a fixed ratio.
Can I use nylon instead of POM?
Sometimes—but moisture and wear behavior differ. If you meant PA66, say PA66 ([PA66 vs aluminum](https://3dwk.com/resources/pa66-vs-aluminum-cnc-prototypes)).
Do plastic parts get needs_manual?
Yes—unparseable solids, absurd tolerances, or process mismatches still route to engineers.
Filled grades and drawing honesty
Glass- or carbon-filled PEEK changes stiffness, wear on cutters, and sometimes anisotropy versus unfilled stock. If the CAD was designed around unfilled modulus, say so when you switch to filled for a hotter test. POM filled grades similarly trade machinability for stiffness. Ambiguous “PEEK or equivalent” lines invite needs_manual because stock selection drives both material $ and cycle time.
Storage, moisture and inspection of plastic prototypes
Even lower-absorbing plastics move with temperature during CMM. Call the inspection temperature if fits are critical. Do not demand metal-like flatness across large POM plates without fixturing notes. For functional demos, label cosmetic machine marks as acceptable on the PDF so estimators do not add unnecessary finishing passes.
Parallel metal stand-in strategy
Some teams CNC aluminum first for fit, then cut POM/PEEK for insulation or wear. That is valid—upload as separate **Example part** intents rather than one confused drawing that mixes anodize notes with plastic stock. Separate lines keep [quote-new.php](https://3dwk.com/quote-new.php) parse and DFM notes readable.