Guides / Machining
What to Decide Before PEEK Goes on a Drawing
September 26, 2026
Sources: manufacturer datasheets and published standards. See editorial standards.
Three decisions sit behind every machined PEEK part: which grade, what tolerance, and whether residual stress gets relieved before the part ships. Get one wrong and the other two do not save you. This is the order to make them in, and what each one costs if you skip it.
Decision 1: grade
Grade is the first decision because it sets the ceiling for everything after it. A part specified in unfilled PEEK and then given a GF30 tolerance and a bearing-grade wear callout is asking one grade to behave like three.
The short version, covered in full on PEEK grades compared:
| Grade | Pick it for | What it costs you elsewhere |
|---|---|---|
| Unfilled | Steam, chemicals, toughness | Creeps under sustained load above 150 °C |
| GF30 (glass filled) | Stiffness and creep resistance while hot | Poor on sliding or wear surfaces |
| CF30 (carbon filled) | Dimensional stability, heat transfer, static dissipation | Loses electrical insulation |
| Bearing grade | Dry running wear surfaces | Not a structural grade |
| Implant grade | Documented biocompatibility | Priced and lead-timed differently, see below |
If the part touches more than one of these needs, something has to give. Write down which requirement is non-negotiable before you pick a grade, not after a quote comes back higher than expected.
Decision 2: tolerance, feature by feature
Once the grade is set, the next question is not “what tolerance can this shop hold” but “which features actually need one.” PEEK’s thermal expansion, roughly four times a machining steel’s per degree, means a tolerance that is trivial at room temperature can be wrong at service temperature, and a tolerance that looks tight on paper may be irrelevant on a feature that never sees a mating part.
A useful split, detailed in PEEK machining tolerances:
- Fit and function features (bores, shafts, sealing diameters): specify the tolerance and the temperature it applies at. ±0.025 mm is achievable on small, annealed, carbon-filled features. ±0.05 mm is the realistic default everywhere else.
- Form and cosmetic features: leave these at a standard machining tolerance. Tightening them adds inspection time and rejection risk for no functional gain.
- Assembly-critical dimensions across a temperature range: this is where the calculator matters more than the tolerance table. Use the thermal fit calculator to see what a nominal clearance becomes at your actual service temperature before you commit a number to the drawing.
Tightening a tolerance on a feature that does not need it is the most common way a PEEK quote comes back high. It is also the easiest one to fix, because it costs nothing to relax.
Decision 3: does this part need stress relief
Residual stress is the variable buyers most often leave off a drawing entirely, and it is the one most likely to make a part that measured correctly at the shop measure wrong on your bench weeks later.
Stock PEEK ships stress relieved. Machining removes material asymmetrically, which unlocks stress that was balanced in the round or plate and lets the part move as it redistributes. Thin walls, deep pockets, and bores machined close to an edge are the features most likely to move.
The rule of thumb, covered fully in annealing PEEK parts: if a wall is thin relative to the part’s overall section, or a feature is held to a tolerance tighter than ±0.05 mm, specify a stress relief anneal between roughing and finishing, not just before shipment. Annealing after finishing only relieves stress that has not already moved the finished dimension.
If you are not sure whether a specific wall thickness needs it, the annealing cycle calculator will size a cycle from the thickest section so you can put a real ramp and soak time on the drawing instead of leaving it to the shop’s judgment.
Putting it on one drawing
A specification that answers all three decisions reads like this, not like three separate notes:
Material: PEEK CF30, per manufacturer datasheet. Critical bore Ø12.000 +0.000/-0.025 mm at 23 °C. Stress relieve after roughing, before finish pass on critical bore. All other features: standard shop tolerance.
That is a specification a shop can quote accurately on the first pass, because none of the three decisions are implicit.
Where implant grade changes the sequence
If the part is implant grade, the sequence above still holds, but a fourth item sits alongside it: documentation. Implant grade PEEK is sold to ASTM F2026 with lot traceability, and a machined part carries that paperwork chain rather than a certification of its own. Specify the standard the stock is sold to, not just the word “implant grade,” because the paperwork is what the quote and the lead time are actually priced against.
What this means for your RFQ
Send the grade, the tolerance on the features that need one with the temperature it applies at, and a stress relief instruction if the part has thin sections or tight fits. A shop that receives all three can quote once, accurately. A shop that has to infer any of them either pads the price to cover the risk or gets it wrong.
The specification is step two of our guide to custom PEEK parts, which goes on to quotes, paperwork and the first parts.
Send the drawing with those three decisions made, and we match you with shops that quote it once instead of guessing.
Frequently asked questions
What is the single biggest specification mistake on a PEEK drawing?
Copying a metal tolerance onto every feature. PEEK moves more than metal with temperature and with residual stress, so a blanket ±0.02 mm callout usually prices the whole part at the cost of its tightest feature for no functional reason.
Can one drawing specify grade, tolerance and stress relief all at once?
Yes, and it should. Grade decides how much the part will move, tolerance decides which features actually need that control, and a stress relief note tells the shop when to anneal. Leaving any one of the three off shifts the decision, and the cost, onto whoever quotes it.
Who decides whether a part needs annealing, the buyer or the shop?
The buyer decides by specifying wall thickness, tolerance and service temperature. The shop decides how to meet that. A drawing that specifies the outcome without dictating the process gives a competent shop room to do it well.
Need a quote for this part?
Send the drawing. We match you with up to 3 shops that cut your PEEK grade and reply within 24 business hours.
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