CNC plastic parts for electronic products

• 1
  Why plastic parts stay in the electronics bill of materials
• 2
  What actually happens when a cutter meets polymer
• 3
  Which polymers hold tolerance in electronic hardware
• 4
  Wall thickness, corners and threads that survive machining
• 5
  Where five-axis changes the outcome for plastic parts
• 6
  Inspection and finishing after the cut
• 7
  Machining versus molding for electronic plastic parts

Inside most electronic products, plastic does jobs metal cannot do cheaply. It insulates, it lets radio signals pass, it damps vibration, and it keeps weight down. A connector body, a board carrier, a lens holder, a battery spacer: none of them carry structural load, but all of them position something that does.

Machining enters the picture when the geometry is not a simple shell. A housing with a stepped internal cavity, a slot for a flex cable, a snap feature that must seat a display within 0.05 mm, all of these are hard to mold before the design is frozen. Cutting them from a billet takes days, not weeks of tooling.

There is also the material question. Polymers such as PEEK, POM and PC are available as rod or plate in small quantities. A molder buys resin by the bag and runs a tool that costs real money. For 50 parts, that math rarely closes.

The trade-off is cycle time. A mill removes material one pass at a time, so per-part cost stays high no matter the quantity. CNC plastic parts for electronic products make sense from one unit to a few thousand, and stop making sense once the design is stable and volume climbs.

• 1
  InsulationMost engineering plastics are dielectric; no coating needed.
• 2
  RF transparencyABS, PC and PP do not shield antennas the way aluminum does.
• 3
  WeightRoughly one-sixth the density of aluminum for the same volume.
• 4
  Design freedomUndercuts and internal steps are cut, not molded.

Metal cutting is mostly about shear. Plastic cutting is about heat and elasticity. Polymer chips soften at the tool tip, then smear back onto the finished surface. The result is a built-up edge, a fuzzy burr, or a melted stripe that no amount of polishing will fully remove.

The fix starts with sharpness. We run polished two-flute and single-flute carbide cutters with high rake angles, often the same geometry used for aluminum. A worn tool that still cuts steel will burn a POM edge. Tool life is measured in edges, not hours.

Next comes evacuation. Plastic chips are light and springy, so they pack into pockets and recut. High helix angles and strong air blast clear them. Coolant is a mixed blessing: it controls heat but can leave stress marks on PC and PMMA.

Feeds and speeds run opposite to metal. Spindle speed goes up to 12,000–20,000 rpm, chipload stays light, and feed per tooth sits around 0.05–0.15 mm. Cutting too slowly generates more heat than cutting fast, which surprises people who learned on steel.

ABS is the default. It machines cleanly, takes a matte finish, and costs little. It is also hygroscopic and creeps under load, so it is a poor choice for a part that must hold 0.02 mm over a year at 60 °C.

PC is stiffer and clearer, and it takes a better thread. It also stress-cracks around sharp internal corners and turns gummy if the cutter dwells. We slow the feed and add a finishing pass to avoid the clouded edge.

POM, often called Delrin, is the best all-round machining plastic. Its chips break cleanly, it holds ±0.05 mm easily on a stable part, and it has a low friction coefficient, which matters for sliding latches and cam tracks. It does not bond well and it is hard to paint.

PEEK and PEI (Ultem) enter when the part sits near a power stage or a reflow oven. PEEK machines like a dense hardwood: slow, hot, and expensive, but it keeps its shape past 250 °C. For most consumer electronics, the cost is not justified. For test sockets and high-temperature fixtures, it usually is.

• 1
  ABSCheap, easy, low stiffness and poor creep resistance.
• 2
  PCStiffer and clearer; watch stress cracking at corners.
• 3
  POMBest chip control and dimensional stability in the group.
• 4
  PEEK / PEIHigh temperature and chemical resistance at high cost.

Wall thickness is the first number to check. Below 1.0 mm, cutting forces push the wall away from the cutter and the part sings. Between 1.5 mm and 4 mm, machining is comfortable. Above 6 mm, consider whether the mass is doing anything, because you are paying for removed chips.

Internal corners cannot be square. A cutter has a radius, so every pocket corner carries at least the tool radius. If the drawing calls for R0.5 and the pocket is 30 mm deep, the tool needed to reach the bottom is too slender to survive. Either open the radius or accept a stepped floor.

Threads in plastic are best cut, not tapped to full depth. A cut thread leaves a cleaner flank and less hoop stress. For M3 and smaller in POM or PC, we often recommend a molded-in metal insert or a heat-set insert instead, because repeated assembly strips plastic threads quickly.

Bosses and ribs need draft on the outside if they will be released from a mold later, but for a machined prototype the concern is different: sharp rib roots act as stress risers. A 0.5 mm fillet at the root adds almost nothing to cycle time and a lot to drop-test survival.

A three-axis mill reaches a part from one direction. Anything on the side faces becomes a second or third setup, and each setup adds a repositioning error. On a plastic part held in soft jaws, that error is often larger than the tolerance itself.

Five-axis work holds the part once and tilts the tool. A curved light-guide channel, an angled connector shroud, or a contoured gasket face can all be finished in one continuous pass. Fewer setups means fewer chances to clamp too hard and leave a witness mark.

Short, stiff tools matter more in plastic than in aluminum. With a tilting head, we keep the cutter short and reach the feature by rotating the part rather than by hanging a long tool out of the spindle. That is the difference between a clean floor and a chattered one.

GreatLight runs 16 simultaneous five-axis machining centers, alongside 12 four-axis mills and 27 three-axis machines. For plastic work, the five-axis cells handle contoured housings and complex internal geometry; simpler plates and spacers stay on three-axis machines where the cycle is faster.

Plastic moves after machining. A part cut in the morning can measure differently in the afternoon as it absorbs moisture and releases internal stress. For tight features, we let the part rest before final inspection rather than measuring hot off the machine.

We inspect 100% of parts before shipment, with raw material checks, in-process monitoring and a final dimensional report available on request. On plastic, the critical measurements are usually hole position, boss height and flatness of a sealing face, not overall length.

Finishing options for plastic are narrower than for metal. Bead blasting gives a uniform matte surface and hides tool marks. Tumbling softens edges. Polishing brings PC and PMMA toward optical clarity, though a machined surface will never match a polished mold.

Laser marking works on most dark or filled polymers and needs a minimum character height of 1.5 mm to stay legible. Painting and plating are generally metal processes; on plastic, we recommend choosing a colored stock or a textured finish instead.