Capabilities · Materials
Polycarbonate machining
Polycarbonate machining is the CNC milling of polycarbonate, a transparent, impact-resistant engineering thermoplastic, into finished components. BELL Machine Works machines clear and pigmented polycarbonate to ±0.001", including flow channels down to 0.4 mm, at our shop in Gilroy, California.
Why engineers specify polycarbonate
Optical transparency. The reason it gets chosen more than any other. If someone has to see the fluid, the cell culture, the mechanism or the fill level, the part is probably polycarbonate.
Impact resistance far beyond acrylic. It deforms rather than shattering, which is why it survives handling and vibration where clear alternatives crack.
Dimensional stability across temperature, electrical insulation, biocompatibility in laboratory and medical grades, and UV resistance in stabilized grades.
Where it fails: it is chemically vulnerable. Many solvents, some cleaning agents and certain adhesives will craze or attack it, and a part that is fine in service can be ruined by the wrong wipe-down. It also scratches more easily than glass.
Why machining it is difficult
Polycarbonate is not hard to cut. It is hard to cut while keeping it clear, and clarity is usually the entire reason it was specified.
It melts before it burrs. A low glass transition temperature and no heat conduction away from the cut. A dull tool, too little chip load or a rubbing cutter puts heat into a small area and the surface goes hazy, permanently. On a part someone needs to image through, a hazy surface is a scrapped part.
It crazes. Fine internal cracking appears under stress, and machining stress is stress. Aggressive cuts, sharp internal corners and clamping pressure all cause it, and crazing is worse under later chemical exposure.
Stress is already in the stock. Extruded polycarbonate carries internal stress from manufacturing. Machining releases it, and a flat plate can bow after the second operation. Cast grades are more stable and cost more.
Chips weld. Molten polycarbonate sticks to the flute, the flute stops clearing, and the tool goes from cutting to rubbing to melting in a short distance. Chip evacuation is not housekeeping here. It's the process.
Finish is the function
On clear polycarbonate the surface is not cosmetic. The reason anyone specifies the material is that they need to see through it, and a hazed surface is a scrapped part. Polycarbonate hazes permanently when a tool stops cutting and starts rubbing. There is no polishing it back.
We finish polycarbonate straight off the machine, with no flame polishing, vapour polishing or secondary operation. Where glare rather than clarity is the problem, a bead blast is the right answer: a matte surface scatters reflection while leaving optical access intact for imaging.
Against a standard callout of 125 μin Ra, we measure 32 μin Ra on a profilometer, on a surface someone specified because they need to see through it.
Parameters we hold in polycarbonate
| Standard tolerance | ±0.001" |
| Minimum feature | Ø0.010" (0.25 mm), to 8:1 depth-to-diameter · 0.4 mm channels machined |
| Grades | Clear and pigmented; cast where flatness across thin sections governs |
| Finishes | Machined, or bead blast to cut glare while preserving optical access |
| Governing difficulty | Melting, crazing, stress release, chip welding |
What we machine in polycarbonate
Microfluidic manifolds and flow geometry. Complementary halves carrying serpentine bypass and return loops at 0.4 mm channel width, over mounting foundations with threaded fluidic ports. Channel width governs whether flow stays laminar, so the tolerance is functional rather than cosmetic. And the part has to stay optically clear, because researchers image live cultures through it.
Mirrored component pairs. Left and right cable clamps with contoured gripping channels, vertical retention walls and integrated mounting bases, in UV-stable grades for outdoor and wide-temperature service. Symmetry across a mirrored pair is a programming and inspection problem as much as a machining one.
Test and calibration fixtures with precision hole patterns for sensor mounting, where optical clarity is functional: it lets a vision system be tested through the fixture rather than around it.
Viewing plates and optical-access windows for equipment where the process has to be visible.
Specifying a polycarbonate part
Say whether clarity is functional or cosmetic, and on which surfaces. There is no reason to pay for optical quality on a face nobody looks through. Tell us the chemical environment, including cleaning agents; this is the most common way a good polycarbonate part fails in service. Avoid sharp internal corners where you can. Consider cast over extruded if flatness across a large thin part matters. That review is part of every quote.