Affordable CNC Plastic Processing in China Wholesale

ABS and PC are the two workhorses. ABS cuts clean, holds a thread, and takes bead blasting without looking chalky. PC is tougher and more transparent-friendly, but it is notch sensitive and builds heat at the cutter, so feeds stay conservative. POM is the choice when you need low friction and tight dimensional stability: gears, bushings, sliding blocks. PMMA gives you optical clarity and polishes well, but it chips at the exit edge if the tool path does not support the cut.

PEEK and carbon-fibre-filled grades sit at the other end. They are stiff, abrasion resistant, and expensive per kilogram, so they suit small functional parts rather than large panels. Carbon fibre loading dulls cutters quickly, which shows up as a higher per-part price. PA (nylon) absorbs moisture and moves after machining, so a part checked the day it comes off the machine may not match the same part a week later in a humid room.

Soft and gummy grades are the ones to avoid when tolerance matters. PP and HDPE cut easily but deflect under clamping pressure and burr heavily. If your geometry is mostly flat and the tolerance is loose, they are fine and cheap. If you need ±0.005 mm on a thin wall in PP, expect scrap.

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  ABS, PC, POMEveryday engineering plastics; good dimensional control and clean threads.
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  PMMAOptical and display parts; needs sharp tooling and supported exits.
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  PEEK, carbon fibreHigh stiffness and heat resistance; higher tool wear and part cost.
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  PP, HDPECheap and chemical resistant; soft, burr-prone, poor for tight tolerance.

Wall thickness is the first thing we look at. In plastic, a 0.8 mm wall can be machined, but it will move when the clamps come off unless the part is supported or the cutting sequence is planned around it. Below 0.5 mm, deflection during cutting usually decides the result rather than the machine accuracy. Tell us the minimum wall on the drawing so we can plan workholding.

Deep pockets and tall thin ribs are the second constraint. A 6 mm end mill reaching 40 mm deep will chatter in plastic unless the tool is necked or the depth is stepped. Sharp internal corners are a related problem: a cutter has a radius, so a true 90° internal corner is a drawing error in most cases. Add a corner radius at least 0.5 mm larger than the smallest practical cutter.

Undercuts and side features are where 5-axis earns its place. On a 3-axis machine, an undercut means a second setup and a re-fixture, and the second setup is where position error creeps in. On one of our 16 simultaneous 5-axis centres, the part is cut in one clamping, so the relationship between features stays as drawn. This matters most on manifolds, housings, and any part with features on four or more faces.

Material is usually the smaller line on a plastic job. A 200 g POM block costs little; the same mass in PEEK or carbon-filled stock can cost many times more. That single choice can move a quote more than any negotiation on hourly rate. If the part does not need high temperature or chemical resistance, ABS or POM will do the same job for far less.

Machining time is the bigger variable. A part with deep pockets, thin walls, and a fine surface finish takes longer than its size suggests, because the cutter has to step down carefully and the finishing pass runs at a small stepover. On a simple bracket, one setup and a few minutes of cutting is normal. On a five-face housing with a sealed bore, you are paying for the 5-axis setup, the probing, and the inspection.

Then there is yield. Plastic parts are scrapped for chatter marks, dimensional drift after clamping, and burrs on soft grades. A shop that quotes a thin-wall PP part at a rigid-resin price is either very good at it or has not run it yet. We would rather quote the realistic cycle and tell you which features are driving it, so you can decide whether to loosen a tolerance or change a radius.

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  Resin choicePEEK and carbon-filled stock can dominate the material line.
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  Cycle timeDeep pockets and fine finishes add cutting hours, not material cost.
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  Setup countEvery extra fixture is a chance for position error and added labor.

Ask what resin grade is actually in the quote. "PC" is not a specification. PC from one supplier and PC from another can differ in melt flow and internal stress, and a machined part will show that difference as warpage or crazing. We list grades on the quote and keep the material certificate with the job.

Ask how the shop handles moisture-sensitive resins. PA and some PC grades need drying before and sometimes during machining. A shop that pulls stock off an open shelf in a humid workshop will produce parts that measure differently next week. This is a process question, not a price question, and the answer tells you more than the hourly rate.

Ask about inspection on plastic specifically. Plastic is soft, so a caliper squeezed too hard reads a smaller number than the true size. Good shops use controlled force gauges or optical measurement on plastic, and they check after the part has settled rather than immediately at the machine. Our inspection runs raw material check, in-process monitoring, and final inspection before shipment, with reports on request.

Finally, match the process to the quantity. Machining from stock makes sense from one piece up to a few thousand, and it is the fastest route to a functional prototype. Above that, injection moulding usually wins on unit cost, and the machined parts become your bridge to the tool. Knowing where that crossover sits for your part keeps you from overpaying on either side.