Capabilities · Materials
PTFE machining
PTFE machining is the CNC milling and turning of polytetrafluoroethylene, the material most people know as Teflon, into finished components. BELL Machine Works machines virgin and filled PTFE to ±0.001" for flight programs, semiconductor equipment, laboratory and chemical-process applications from our shop in Gilroy, California.
Why engineers specify PTFE
Chemical inertness. Unreactive to nearly every industrial solvent, acid and base. It is the default when a part sits in a fluid path nothing else survives: propellants, pressurants, solvents.
Temperature range. Serviceable from cryogenic temperatures through roughly 500 °F, which is why it appears in cryogenic and propellant systems.
The lowest friction of any solid polymer, and self-lubricating.
Dielectric strength, making it a standard insulator in RF and high-voltage assemblies.
Non-stick and non-marring, so it can contact finished surfaces without scratching them.
Why PTFE is difficult to machine
Everything that makes PTFE useful makes it hard to hold a dimension in.
It is very soft. PTFE has a Shore D hardness in the 50s. Tooling pressure that would barely register on Delrin pushes PTFE out of the way, and the material returns after the cutter passes, so the programmed dimension and the finished dimension are two different numbers.
Thermal expansion is extreme, roughly ten times that of steel, and the coefficient itself changes across the temperature range. A PTFE part measured on a warm bench and installed in a cryogenic line is not the size anyone wrote on the drawing. Tolerance callouts on PTFE need a temperature attached to be meaningful.
It cold-flows. Under sustained load, PTFE creeps, permanently. A clamped PTFE part slowly changes shape, which affects both how you fixture it during machining and how it behaves in service.
It burrs relentlessly. Soft, ductile and low-friction, PTFE tears rather than shears unless tooling is genuinely sharp. Dull tooling produces a fuzzy edge that no amount of deburring fully cleans up.
Filled grades machine differently. Glass-, carbon- and bronze-filled PTFE are dimensionally more stable and stiffer than virgin, but the fillers are abrasive and consume tooling. Glass-filled in particular is hard on cutters.
Finish
PTFE is the material where the difference shows most. It tears rather than shears the moment a tool is past its best, and the fuzzy edge that results never fully cleans up by hand. Deburring afterwards leaves a rounded, uneven edge where a crisp one was specified.
We finish PTFE straight off the machine, with no secondary operation. Getting it right at the cutter is the only way it comes out right.
Against a standard callout of 125 μin Ra, we measure 32 μin Ra on a profilometer, on the part as it leaves the fixture, with nothing done to it afterwards.
Parameters we hold in PTFE
| Standard tolerance | ±0.001", referenced to temperature |
| Grades | Virgin and filled, white and black |
| Service range | Cryogenic through approximately 500 °F |
| Chemical service | Propellants, pressurants, solvents, acids, bases |
| Geometry routinely cut | Scalloped raceways at varying diameters · matched top-and-bottom halves · tabbed mounting ears · sealing faces and grooves |
| Part families | Multi-part-number families machined as matched sets |
What we machine in PTFE
Line and tube raceway clamping. Matched halves that bolt around parallel fluid lines and secure to structure through tabbed ears. Each half carries scalloped raceways cut to different tube diameters, and both halves have to align across a whole part family, which is why these arrive as multi-part-number sets rather than single brackets, and why they are a fixturing problem before they are a cutting problem.
Seals, sealing plates and gasket geometry, where groove dimension and surface condition determine whether the seal holds.
Insulators and dielectric components for RF and high-voltage assemblies.
Fluid-path components where nothing else survives the chemistry.
Non-marring contact hardware, where a part touches a finished surface that cannot be scratched.
Grades: virgin PTFE in white and black; glass-, carbon- and bronze-filled on request.
Specifying a PTFE part
A few things worth deciding before you send the drawing. Attach a temperature to your tolerances, on PTFE, ±0.001" without a reference temperature isn't a specification. Consider a filled grade if the part carries load or must hold a dimension over time; virgin PTFE will cold-flow. Expect a limit on wall thickness and unsupported features that would be routine in Delrin. And tell us the service environment, because cryogenic, high-vacuum and chemical service each change what we'd recommend.
That conversation happens inside the quote. Our DFM review is part of every one.