POM, PEEK, nylon, PC and acrylic milled multi-face on five-axis centers. Plastic behaves differently from aluminium, so the process is planned around heat, spring-back and burrs before the first cut.
Plastic is not soft metal. It conducts heat badly, it deflects under the cutter and it burrs instead of chipping, so a program written for aluminium produces a different part.
Cutting heat has nowhere to go in plastic, so it stays at the edge until the surface smears or burns. A scorched PEEK face cannot be polished back, which makes the cutting data and the cooling method a design decision rather than a shop preference.
A wall deflects under the cutter and springs back after the tool has passed, so the finished section is thinner than the program intended. Where the wall is very thin, the fix is a supported setup and light finishing passes, not a smaller feed.
Plastics leave a fine burr or fuzz where metals break a chip. Left to the end of the job it becomes a hand-finishing queue, and every hour of deburring is an hour the part is not in your test rig.
PA absorbs moisture from the air, so a part machined dry measures larger once it has settled. That is the material, not a machining error, and it has to be designed for rather than argued about at incoming inspection.
Each one addresses a way plastic differs from metal: heat that cannot escape, walls that push back, and dimensions that move after the machine is finished with them.
Aluminium carries cutting heat into the chip and the workpiece; plastics keep it at the edge, which is how PEEK and PC scorch or smear. Sharp tool geometry, generous clearance and an air blast instead of flood coolant keep the cut cool and the surface even.
On deep pockets we reduce the step-over and keep the tool moving rather than pushing the feed. A slower program that produces a clean part costs less than a fast one that produces a part you cannot send out.
A thin plastic wall deflects away from the cutter and springs back once the tool has gone. The result is a section that is thinner in the middle than at the ends, and a part that fails the check without any obvious machining mistake.
The answer is sequence rather than force. Leave stock on during roughing, let the part come back to rest, then take light finishing passes with short tools. Large flat sections of PEEK or PC are stress-relieved between roughing and finishing when the part has to stay flat.
PA takes up moisture from the air, and a part machined dry will be measurably larger a week later. The two practical answers are tolerances that accommodate the swell, or a grade with lower moisture uptake.
Where a dimension really has to hold, we say so at quotation stage. Agreeing whether parts are inspected dry as machined or after conditioning removes most of the disagreement, because on these grades that decision changes the number more than the machining does.
Start from the requirement that dominates, whether that is stiffness, wear, temperature or chemical exposure, and the shortlist is short.
| Grade | Temperature | Wear and stiffness | Chemical resistance | Typical parts |
|---|---|---|---|---|
| POM (acetal) | Up to about 90 °C continuous | Stiff and dimensionally stable; the best all-round machinable plastic | Good against fuels, oils and solvents | Gears, bushings, precision slides, fixtures |
| PA (nylon 6/6) | Up to about 100 °C | Tough and impact resistant; absorbs moisture and moves with humidity | Good against oils, attacked by strong acids | Brackets, wear pads, covers, prototypes |
| PEEK | Up to about 250 °C | Very stiff for a plastic, with excellent wear behaviour at temperature | Resistant to most solvents and to steam | Aerospace and medical hardware, semiconductor parts |
| PC (polycarbonate) | Up to about 120 °C | High impact strength, with transparent grades available | Poor against alkalis and it stress-cracks with some solvents | Guards, windows, housings, lens holders |
| PMMA (acrylic) | Up to about 80 °C | Rigid and optically clear, but brittle under impact | Good against alcohols, attacked by acetone | Display parts, light guides, transparent covers |
| ABS | Up to about 80 °C | Easy to machine and bond, with moderate stiffness | Moderate, and sensitive to ketones | Prototype housings, panels, jigs |
Most plastic jobs use two or three of these, and the finishing steps are quoted separately so you can see what each one costs.
Multi-face parts cut in one setup, including pockets and bores that would otherwise need several fixtures.
Bushings, rollers and sleeves turned from rod and bar, with milled flats or cross holes in the same program.
Pockets machined for heat-set inserts, threads tapped to suit the grade, and bonded surfaces prepared.
Between roughing and finishing on large or heavily machined sections, where the material allows it.
PC and acrylic machined to a clear finish, with polishing or vapour polishing quoted as its own operation.
Critical features measured with reports on request, against a measuring condition agreed before the parts are cut.
| Feature | What we check | Why it matters |
|---|---|---|
| Wall thickness | Whether the wall can be cut without chatter or spring-back | Thin walls deflect in soft grades and crack in brittle ones when they are released |
| Internal corners | Corner radius against the tool diameter | A square internal corner cannot be produced by a round cutter |
| Threads | Thread type and engagement depth | Threads in plastic strip sooner than in metal, so an insert often lasts longer |
| Holes | Depth-to-diameter ratio and straightness | Deep small holes wander in plastic, and reaming can smear rather than cut |
| Flatness | Whether the part is measured as machined or after stress relief | Large flat sections of PEEK or PC move after machining |
| Surface finish | Which faces are cosmetic | Polishing and vapour finishing are separate operations with their own lead time |
Plastic machining is judged after the part has settled, not the moment it leaves the machine. These are the numbers and the practices behind that.
Our stated machining tolerance, held on the features you call out and on dimensions the drawing leaves open, with ±0.0002 in as the imperial equivalent.
Fine finishing reaches Ra 0.2–0.8 μm on grades that polish, and we say when a grade will not hold that.
POM, PA, PC, PMMA, ABS and PEEK are held in common sheet and rod sizes, so a design change does not wait behind a material order.
Roughing with stock left on, then finishing in light passes after the last clamp change, so thin walls are measured as released.
One part is a normal order and runs on the same five-axis centers as production work, with the same inspection.
Price, lead time and manufacturability notes within 12 hours, including a straight answer on whether the grade and the wall thickness will hold the tolerance you asked for.
Enclosures and internal chassis where wall thickness and shielding clearance decide the design.
Trim, ducting and build-support parts that have to survive a hot bay without a mould being cut.
Small actuated components and fixtures machined under ISO 13485 process control, with documentation on request.
On a stable section in a grade like POM, yes. ±0.005 mm / ±0.0002 in is our stated tolerance, applied to the features you call out and to dimensions the drawing leaves open.
On thin walls, wide flat panels or a hygroscopic grade like PA, the part moves with humidity and temperature, so a realistic tolerance plus a note about the environment is worth more than a tight number nobody can hold twice.
Where the material allows it and the part is likely to move, such as large PEEK or PC sections or parts with a lot of material removed, we will stress-relieve between roughing and finishing.
Tell us whether the part will be measured cold and used hot, because that decides which dimensions should be tight.
POM, PA nylon, PC, PMMA, ABS and PEEK are the everyday grades, with sheet and rod stock in common sizes held in-house. Filled grades such as carbon-filled PEEK and PTFE are ordered per job, and that lead time is included in the quotation.
We machine the pockets for heat-set inserts, tap threads to suit the material and prepare bonded surfaces. Threads in plastic strip more easily than in metal, so where a fastener will be cycled often we usually suggest a heat-set insert or a coarser thread rather than a deeper tapped hole.
PC and acrylic machine to a clear finish, and fine machined surfaces can be polished or vapour polished where the geometry allows. Truly optical clarity is a polishing process rather than a milling one, so it is quoted separately with its own lead time.
One part. Prototype quantities have no minimum order and run on the same five-axis centers as production work with the same inspection, so a single test article behaves like the parts that follow it.
Critical features are measured before shipment with reports on request, and we agree the measuring condition first: as machined, conditioned, or after stress relief. On hygroscopic grades that decision changes the numbers more than the machining does.
Quotation and a free DFM analysis within 12 hours, production starting within 24 hours of approval, and parts shipping in 3–5 days on standard grades. Filled or specialist materials are scheduled to their own stock lead time, which is stated in the quotation.
We will tell you whether the wall thickness, the grade and the tolerance line up, and what it costs to machine, before you commit to a mould or a long-lead material order.
No minimum orderStress relief where neededInserts and threadsConfidential uploads
Trusted by engineers and manufacturers worldwide
Upload your 3D model or 2D drawing and get a quotation with a free DFM analysis. Maximum processing size 4,000 mm.
CNC Metals 13 grades
CNC Plastics 10 grades
Machines & processes 12 options
Surface & post-processing 10 options
Material: not selected Machine: not selected Post-process: not selected
Fill in this short form and we'll open WhatsApp with your message ready to send. We only use these details to reply to you.
Nothing is sent until you press send inside WhatsApp.
