Guides / Machining

PEEK Machining: What Is Realistic on a Drawing

September 20, 2026

Sources: manufacturer datasheets and published standards. See editorial standards.

PEEK is the plastic engineers reach for when acetal and nylon run out of temperature, when metal is too heavy or too conductive, and when the part has to sit in steam, solvents or body fluids for years. It also costs many times more per kilo than the plastics it replaces, so the drawing you send matters more than usual.

This guide covers what a machine shop actually does with PEEK, which decisions change the price and what to specify before you ask for a quote.

What PEEK is

PEEK is polyetheretherketone, a semi crystalline thermoplastic in the PAEK family. The properties that get it specified are consistent across suppliers:

Property	Typical value, unfilled
Glass transition temperature	143 °C
Melting point	343 °C
Continuous service temperature	about 250 °C
Tensile strength at 23 °C	90 to 100 MPa
Density	1.30 g/cm³
Water absorption, 24 hours	about 0.1%
Thermal expansion below Tg	about 47 µm/m·K

Two numbers explain most of what happens in the shop. The first is the glass transition at 143 °C: above it the material softens and expansion jumps, so a part that has to hold a fit at 200 °C behaves very differently from the same part at room temperature. The second is thermal conductivity, which is low. Heat from the cut does not leave through the part, so it goes into the tool and into the surface of the cut.

How PEEK behaves on the machine

Shops that run PEEK regularly tend to work the same way.

Sharp, polished tooling. Dull edges rub instead of cutting, and rubbing puts heat into a material that cannot get rid of it. Shops use high rake, polished flutes and tools kept for plastics only. A tool that has been in steel will smear PEEK.

Chip evacuation over cutting speed. A chip that stays in a slot melts and welds itself to the wall. Air blast or flood coolant is normal, and deep pockets are cut in steps.

Stress management. Extruded rod and plate hold internal stress from the way they were cooled. Remove material from one side and the part moves. On thin walls, deep bores and long slender parts, shops rough the part, anneal it, then finish it.

No sharp internal corners. PEEK is tough, but a sharp internal corner concentrates stress, and a part that fails in service usually fails there. A small radius costs nothing on the drawing and a lot in the field.

Filled grades wear tooling. Glass and carbon fibre are abrasive. Tool life drops, and many shops keep separate tools so fibre dust never touches unfilled medical work.

Tolerances you can ask for

A plastic part is not a metal part with a different label. Useful numbers to plan around:

• General machined features: around ±0.05 mm.
• Small features in annealed carbon filled stock: ±0.025 mm, sometimes a little better.
• Flatness and bore roundness on thin parts: better after a stress relief cycle, and worse if the part is clamped hard.
• Surface finish: Ra 0.8 µm is normal, finer with a finishing pass and the right tool.

Then there is temperature. PEEK expands roughly four times more than steel per degree. A 100 mm feature held to ±0.025 mm at 20 °C can move well past that tolerance at 150 °C. If the fit has to work hot, say so, and give the temperature. Carbon filled PEEK expands about half as much as unfilled, which is one of the main reasons it gets specified for fixtures and wafer handling parts.

What to put on the drawing

Six things decide whether a quote comes back useful or full of assumptions.

1. The grade. Unfilled, GF30, CF30, bearing grade or implant grade stock to ASTM F2026. If you do not know, give the temperature, load and media and let the shop suggest one. Our grade comparison covers the trade-offs.
2. The service temperature. Continuous and peak. This changes the grade and the tolerance discussion.
3. The media. Steam, solvents, acids, body contact or food contact. This changes the stock and the paperwork.
4. Critical features only. Tolerance the bore that has to fit. Leave the rest open. Every tight feature you do not need adds passes and inspection.
5. Thin walls and deep bores. Flag them. They are what decide whether an annealing cycle is in the quote.
6. Documents. Lot certificate, ISO 10993 or USP Class VI data, cleanroom packing. Ask up front. Adding them after the parts are cut usually means cutting them again.

Where machined PEEK ends up

Medical devices use it for instrument handles, guides and trays that go through hundreds of autoclave cycles, and for parts cut from implant grade stock. Semiconductor fabs use carbon filled grades for wafer handling combs, end effectors, CMP retaining rings and test sockets, where outgassing and particles are checked. Oil and gas uses it for seal backup rings, valve seats and downhole insulators that see pressure and hot fluid. Process and lab equipment uses it wherever the fluid path has to stay inert.

What these have in common is that the part is small, the quantity is modest and failure is expensive. That is also why a shop that machines PEEK weekly is worth finding.

Choosing a shop

Questions worth asking any shop that quotes your PEEK part:

• How often do you run PEEK, and which grades?
• Do you keep separate tooling for plastics, and for filled grades?
• Do you have an annealing oven, or do you send stress relief out?
• Where does the stock come from, and can you pass through the lot certificate?
• How do you clean and pack the parts?

A shop that answers these quickly has done the work before. A shop that treats PEEK as aluminium with a lower feed rate will deliver parts that warp after the first thermal cycle.

If you would rather not run that search yourself, send the drawing and we match it with shops that already work this way. For the grade, tolerance and stress relief decisions in one place, see what to decide before PEEK goes on a drawing.

Frequently asked questions

Keep reading

• Which Thread Method Works for a PEEK Part: Tap, Mill or Insert
• Specifying Swiss-Type Turned PEEK Parts Without Burrs or Runout