Machining PTFE / Teflon: Speeds, Feeds & Tolerances
PTFE machines easily in one sense and deceptively in another. Cutting forces are low, no coolant is required for most operations, and the material does not work-harden. But PTFE's softness, extremely high thermal expansion, and tendency to deflect and cold-flow under cutter pressure make it demanding for tight-tolerance work. Parts that look correct off the machine can measure out of tolerance after thermal equilibration or after sitting under load. Understanding how these properties interact with tooling and setup is the difference between acceptable and scrap.
At a Glance
- Tooling: sharp carbide preferred; HSS acceptable for light finishing cuts
- Rake angle: 10–15° positive — critical; negative or zero rake causes smearing
- Speeds: 400–1,000 sfm for turning; 300–600 sfm for milling — faster than for steel
- Feeds: 0.003–0.010 in/rev for turning; light passes for finishing
- Coolant: air blast or no coolant (virgin); avoid water-soluble coolants that can contaminate chemical-service parts
- Tolerances: ±0.005 in. routinely achievable; ±0.002 in. with care and temperature stabilization
- Key hazard: thermal expansion — parts measured at 73°F are 0.010–0.030 in. larger at 150°F
Why PTFE Is Challenging to Machine
Softness and Deflection
PTFE's Shore D hardness of 50–65 means thin walls, small-diameter bores, and slender features deflect under cutting pressure before the cutter reaches them. A 0.25-inch-diameter post will bow away from the tool; a bore in a thin tube wall will spring back. Standard fixturing approaches for metal do not transfer directly — you need to support the workpiece close to the cut and use lighter finishing passes.
Thermal Expansion
The coefficient of thermal expansion (CTE) of PTFE is approximately 5.5 × 10⁻⁵ in/in/°F — roughly 10 times that of steel. A 2-inch-diameter PTFE bore that you turn to specification at the bench temperature of 75°F will be 0.007 inches larger if the shop warms to 130°F. For close-clearance fits (e.g., seal grooves or close-bore bushings), measure the part at the intended service temperature or compensate with a predictive offset.
In practice, allow parts to thermally stabilize at room temperature for at least 30 minutes before final measurement after any machining operation that generates heat.
Creep After Machining
PTFE cold-flows under sustained stress, including the residual stress from workholding. If you clamp a rod in a three-jaw chuck tightly, the OD will show chuck-jaw marks when you release it — and those marks represent permanent deformation. Use soft jaws, collets, or backup fixtures with distributed contact area.
Tooling Recommendations
Carbide vs. HSS
Sharp solid carbide tools are the standard choice. The combination of high-positive rake angle and sharp cutting edge prevents the "smearing" effect that occurs when cutting pressure pushes PTFE ahead of the cutter rather than shearing it. Uncoated carbide (C2/K10 grade) works well; TiN or TiAlN coatings are not necessary and offer no meaningful advantage.
HSS tools with fresh edges are acceptable for prototype quantities and light finishing passes. Dull HSS produces immediate surface quality problems — PTFE tells you when a tool needs to be resharpened.
Rake and Relief Angles
| Parameter | Recommended Range |
|---|---|
| Top (back) rake | +10° to +15° |
| Side rake | +5° to +10° |
| End relief | 8°–12° |
| Side relief | 8°–12° |
| Nose radius | Small (0.005–0.015 in.) for finishing |
Negative rake angles cause PTFE to smear and load up on the cutting edge. The material needs to be sheared, not pushed.
Turning
Speeds and Feeds
| Diameter | Surface Speed (sfm) | Feed (in/rev) | Depth of Cut |
|---|---|---|---|
| <0.5 in. | 600–1,000 | 0.003–0.006 | 0.010–0.050 in. |
| 0.5–2 in. | 500–800 | 0.005–0.010 | 0.020–0.100 in. |
| 2–6 in. | 400–600 | 0.005–0.010 | 0.050–0.200 in. |
| >6 in. | 300–500 | 0.008–0.015 | 0.100–0.250 in. |
Run the lathe at speeds toward the higher end of the range for finishing passes; use the lower end for rough stock removal where chatter might be an issue with large billets. PTFE does not benefit from slow speeds the way that metal does — higher speed with a sharp tool consistently produces better surface finish.
Finishing Passes
Leave 0.005–0.010 inches of material for the final pass. Use a light feed (0.002–0.004 in/rev) and full surface speed. Allow the part to cool to room temperature before measuring — frictional heat from turning temporarily expands the workpiece.
Drilling
PTFE drills readily with standard twist drills, but several issues arise in blind holes and deep holes:
- Chip evacuation: PTFE chips are soft and sticky; peck-drill (0.5D peck intervals) for holes deeper than 2× diameter
- Entry burr: PTFE tends to raise a slight burr at the drill entry — a countersink entry pass eliminates this
- Hole size: drilled holes are typically 0.001–0.005 inches oversize due to thermal expansion and spring-back; if a close tolerance is needed, bore or ream to size
Recommended Drill Parameters
| Drill Diameter | Speed (rpm, using sfm ~500) | Feed |
|---|---|---|
| 1/8 in. | ~4,800 rpm | 0.002 in/rev |
| 1/4 in. | ~2,400 rpm | 0.004 in/rev |
| 1/2 in. | ~1,200 rpm | 0.006 in/rev |
| 1 in. | ~600 rpm | 0.008 in/rev |
Use a 118° point angle (standard) or a 135° split point for better centering and reduced thrust force.
Milling
End Milling
Conventional (climb) milling tends to pull the workpiece upward; conventional up-cut milling may smear the surface. Either approach works if the part is well-supported. Use:
- 2-flute end mills for aggressive stock removal (better chip clearance)
- 4-flute end mills for finishing passes (more cutting edges, better surface)
- Full-radius ball end mills for curved surface interpolation
Surface speed: 300–600 sfm; feed per tooth: 0.001–0.005 in.
Fixturing Thin Parts
Thin PTFE sheets (under 0.125 in.) deflect during face milling. Vacuum fixturing is effective for flat parts — PTFE seals well enough to hold under moderate vacuum. Double-sided tape is an acceptable alternative for prototype work but can leave adhesive residue.
Tolerances and Surface Finish
Achievable Tolerances
| Grade | Typical Tolerance | Tight Tolerance (with care) |
|---|---|---|
| Virgin PTFE | ±0.005 in. | ±0.002–0.003 in. |
| Glass-filled (25%) | ±0.003 in. | ±0.001–0.002 in. |
| Carbon-filled (15%) | ±0.003 in. | ±0.001–0.002 in. |
| Bronze-filled (60%) | ±0.002 in. | ±0.001 in. |
Filled grades are dimensionally more stable because the filler reduces thermal expansion and creep. For precision-fit components — seal grooves, close-bore bearings — bronze or carbon-filled grades hold tolerances more reliably than virgin.
Surface Finish
A well-set-up turning operation on virgin PTFE achieves Ra 32–63 µin (0.8–1.6 µm) without difficulty. Finer finishes (Ra 16 µin / 0.4 µm) require sharp carbide, light finishing passes, and adequate spindle speed. PTFE surfaces do not burnish the same way metals do — do not try to lap PTFE to improve surface finish; the material deforms and smears under lapping pressure.
Safety and Housekeeping
PTFE is chemically inert at room temperature. Machining dust is not acutely hazardous, but:
- Ventilation: required if machining heated or near-charred PTFE — decomposition products at temperatures above 260°C are toxic
- No smoking near PTFE dust: cigarette smoke drawn through PTFE particles creates polymer fume fever risk
- Chip disposal: standard non-hazardous waste; PTFE swarf is not reactive and does not absorb oils
PTFE grinding or sanding is not recommended — the process generates fine airborne particles. Use cutting operations (turning, milling, drilling) wherever possible.
For comparison, machining PEEK is more demanding (higher cutting forces, different tool geometry) but PEEK holds much tighter tolerances with lower creep. See the PEEK vs PTFE comparison if dimensional stability is driving your material selection.
For grade selection relevant to machining, see PTFE grades. For stock size availability, see PTFE specifications.
Order PTFE sheet, rod, or tube for machining — cut to size available
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