Materials · PEEK · POM (Delrin) · Nylon · PC · ABS · PTFE
PEEK and plastic CNC machining
PEEK machining services and plastic CNC machining in POM (Delrin), nylon, polycarbonate, ABS and PTFE, from 1 piece. Realistic tolerances, stress relief where it matters and a quote within 12 hours.
Plastic CNC machining from stock rod and plate
CNC machining is the right process for plastic parts when you need a few to a few hundred pieces, when the material must be the real engineering grade (not a 3D-printing substitute) or when the part has features molding cannot produce without a tool. Typical parts: insulators, wear pads, gears and bushings, manifolds, fixtures and jigs, lab and semiconductor components, seals and valve seats.
We machine plastics on the same 3- to 5-axis mills and lathes as metal parts, with sharp tools, low clamping force and attention to heat, because plastics move with temperature, moisture and internal stress far more than metals do. That last point decides which tolerances are realistic; it is covered in detail below.
Plastic grade comparison
Typical values for unfilled, extruded stock shapes. Filled grades (glass or carbon fiber) are stiffer and more stable; ask if you need one.
| Material | Tensile strength | Density | Max continuous temp | Typical uses | Machining notes |
|---|---|---|---|---|---|
| POM (Delrin, acetal) | ~65–75 MPa | 1.41 g/cm³ | ~90–100 °C | Gears, bushings, fixtures, snap parts | Easiest plastic to machine; stable, low moisture uptake |
| PEEK | ~95–100 MPa | 1.31 g/cm³ | ~250 °C | High-temp insulators, chemical and wear parts | Machines well; anneal for tight or thin parts |
| Nylon (PA6 / PA66) | ~75–85 MPa dry | 1.14 g/cm³ | ~80–100 °C | Wear pads, rollers, guides | Absorbs water; dimensions change after machining |
| Polycarbonate (PC) | ~60–65 MPa | 1.20 g/cm³ | ~115–120 °C | Covers, windows, impact-resistant parts | Tough; machined faces are not optically clear without polishing; avoid solvents |
| ABS | ~40–45 MPa | 1.05 g/cm³ | ~70–80 °C | Prototype housings, form-fit models | Easy to machine; low cost; low heat resistance |
| PTFE (Teflon) | ~20–30 MPa | 2.15–2.20 g/cm³ | ~260 °C | Seals, valve seats, chemical-resistant insulators | Very soft; creeps under load; hard to hold tight tolerance |
Delrin machining (POM)
POM, sold under the Delrin brand for the homopolymer, is the first choice for machined plastic parts. It cuts cleanly with good surface finish, absorbs little moisture (about 0.2% in 24 hours), has low friction and is dimensionally stable. If you are unsure which plastic to use for a mechanical part at room temperature, start with POM.
PEEK CNC machining
PEEK keeps useful strength up to about 250 °C, resists almost all common chemicals and is inherently flame retardant. It is one of the most expensive plastics, so stock size and scrap matter. Extruded PEEK contains internal stress; removing a lot of material from one side can make a part bow. For thin or tightly toleranced PEEK parts, the usual route is to rough machine, anneal (a controlled heating and slow cooling cycle that relieves stress) and then finish machine. Tell us if your part needs this; it adds time but makes dimensions stable.
Nylon, PC, ABS and PTFE
Nylon is tough and wear resistant but takes up water: unfilled PA6 can absorb around 2–3% by weight at normal humidity, and grows measurably as it does. PC is the choice for impact resistance and transparency. ABS is low cost and fine for form-fit prototypes. PTFE has the best chemical resistance and lowest friction of any common plastic, but it is soft, deforms under clamping and creeps (cold flow) under sustained load.
PEEK machining tolerances and what plastics can really hold
Our standard tolerance on metal parts is ±0.03 mm. On plastics, a machine can cut to that number, but whether the part still measures it a day later, in a different room, is a different question. Four effects dominate:
- Thermal expansion. Plastics expand roughly 5 to 10 times more than steel. POM is around 110 µm/m·K, PTFE over 100 µm/m·K, PEEK around 50 µm/m·K. A 100 mm POM part grows about 0.055 mm for a 5 °C temperature change, which is more than a ±0.03 mm tolerance band.
- Moisture uptake. Nylon swells as it absorbs water, so a part machined to size in a dry shop can be oversize after weeks in humid air. Avoid nylon for tight fits; use POM instead.
- Internal stress. Extruded stock contains stress that is released when material is removed, making thin or asymmetric parts warp. Annealing PEEK and other high-performance plastics before finishing reduces this.
- Creep and clamping. Soft plastics, PTFE above all, deform under clamping and continue to move under load. Measured dimensions depend on how the part is held.
Realistic tolerances for CNC plastic parts:
| Material | Recommended general tolerance | Tighter, on small critical features |
|---|---|---|
| POM, PEEK (annealed) | ±0.05 mm | ±0.03 mm, confirmed in quote |
| PC, ABS | ±0.05–0.1 mm | ±0.05 mm |
| Nylon | ±0.1 mm | ±0.05 mm, at time of inspection |
| PTFE | ±0.1 mm | ±0.05 mm on small features |
Tighter than ±0.05 mm on plastics is possible on small features, but it costs more and may not survive temperature or humidity changes in use. Specify the temperature at which a critical dimension applies if it matters. See our tolerance guide for how to call out tolerances.
Design tips for machined plastic parts
- Keep walls at 1.5 mm (0.06 in) or thicker, and thicker still for PTFE; thin plastic walls flex under the cutter.
- Avoid fine tapped threads in soft plastics; use threaded inserts for threads that will be assembled more than a few times.
- Use symmetric designs or leave material on both sides of the stock to reduce warping.
- For press fits, design interference for the plastic's lower modulus and higher expansion, not steel rules.
- If you need a transparent PC face, mark it; machined faces are frosted unless polished.
For more on processes, see CNC milling, CNC turning and rapid prototyping. Our cost guide explains how tolerances and setups affect price.
Related
Other materials we machine
Aluminum
When you need tighter tolerances and stiffness at low weight.
303 · 304 · 316Stainless steel
Corrosion-resistant metal for wet, food and chemical environments.
Grade 2 · Grade 5Titanium
High strength-to-weight and corrosion resistance.
All materialsMaterials overview
Every metal and plastic we stock, and how to choose.
FAQ
Plastic machining questions
What tolerance can you hold on PEEK machined parts?
We recommend ±0.05 mm as a general tolerance on PEEK. ±0.03 mm is achievable on small critical features, usually with annealing between roughing and finishing, and is confirmed in the quote.
Is Delrin or nylon better for machined parts?
For most machined parts, Delrin (POM). It is more dimensionally stable because it absorbs very little moisture, and it machines with a cleaner finish. Nylon is tougher and cheaper but swells as it takes up water, so it is a poor choice for tight fits.
Why are plastic tolerances looser than metal tolerances?
Plastics expand 5 to 10 times more with temperature than steel, some absorb water, extruded stock contains internal stress, and soft grades deform under clamping. A part can be cut to size and still move out of tolerance later.
Do you anneal PEEK before machining?
When the part is thin, asymmetric or tightly toleranced, we recommend roughing, annealing and then finish machining. Note the requirement on your drawing or ask for it in your quote request.
Can you machine PTFE (Teflon) parts?
Yes. PTFE machines easily but is very soft and creeps under load, so we recommend ±0.1 mm general tolerance and thicker walls. It is well suited to seals, valve seats and chemical-resistant insulators.