Machining Ertalyte PET — Speeds, Feeds & Tooling Guide
Ertalyte (bearing-grade PET-P) machines readily on standard CNC lathes and mills with carbide or sharp HSS tooling. It produces better surface finishes than acetal on turned bearing bores and holds tighter tolerances than nylon because of its low moisture absorption. Ertalyte TX (PTFE-filled) machines similarly to the unfilled grade with slightly faster tool wear. Neither grade requires special handling, pre-drying, or post-process heat treatment for most bearing applications.
At a glance:
- Turning: 400–600 SFM; feed 0.005–0.010 IPR; positive-rake carbide or sharp HSS
- Milling: 200–400 SFM; 0.003–0.006 IPT chip load; climb milling preferred
- Drilling: 150–250 SFM; parabolic flute drills; coolant for deep holes
- Tapping: spiral flute taps; cutting fluid recommended
- Chip character: long stringy chips (less than acetal) — chip breaking is important
- No pre-drying required; moisture absorption is negligible
General Machining Behavior
Ertalyte PET-P behaves more like a hard engineering plastic than a soft thermoplastic. It does not melt and smear at the cutting edge the way LDPE or UHMW does. Instead, it cuts cleanly — more similar to acetal — but tends to produce longer chips that wrap around the tool if not managed. This is the main practical difference from machining acetal, which breaks chips more readily.
Key behavior notes:
- Chip formation: Long, curling chips. Use chip-breaking tool geometry or program chip-breaking tool paths.
- Heat sensitivity: Ertalyte's HDT is 85°C (264 psi) — this is not a concern under normal cutting conditions with adequate chip clearance, but avoid dwelling on the surface or running without chip evacuation at depth.
- Dimensional stability: Ertalyte holds dimensions well after machining. No moisture conditioning is required before or after — moisture expansion is <0.05% at saturation, meaning machined tolerances are stable in air and water.
- Surface finish: Ertalyte takes a better surface finish than nylon in precision turning — Ra values below 32 µin (0.8 µm) are achievable with sharp tooling and proper feeds.
Turning Parameters
Turning is the primary operation for Ertalyte rod stock into bushings, bearings, and rollers.
| Operation | Surface Speed (SFM) | Feed Rate (IPR) | Tool Material |
|---|---|---|---|
| Roughing | 400–500 | 0.008–0.012 | C-2 carbide or sharp HSS |
| Finishing | 500–600 | 0.003–0.006 | C-2/C-3 carbide, polished rake face |
| OD groove / parting | 200–300 | 0.003–0.005 | Carbide parting blade |
| Internal boring | 300–500 | 0.004–0.008 | Carbide boring bar |
Tool Geometry Recommendations
- Rake angle: Positive, 5–15°. Positive rake reduces cutting forces and chip compression, producing cleaner cuts with less surface tearing.
- Relief angle: 10–15° clearance. Standard for plastics — prevents rubbing on the workpiece below the cutting edge.
- Nose radius: 0.015"–0.032" for finishing. Larger nose radius improves surface finish; too large causes chatter on thin-wall parts.
- Edge condition: Sharp, honed — not highly rounded. Ertalyte responds best to a razor-sharp edge. Dull tooling causes smearing, elevated cutting temperatures, and degraded surface finish.
Tolerances Achievable
Ertalyte rod on a CNC lathe holds ±0.001" on OD and bore diameters reliably. For bearing bores, a reaming pass achieves H7 tolerance (±0.0005" in small diameters). Bore gauging immediately after machining is accurate — no need to wait for moisture equilibration as with nylon.
Milling Parameters
| Operation | Surface Speed (SFM) | Chip Load (IPT) | End Mill Type |
|---|---|---|---|
| Face milling (roughing) | 250–350 | 0.005–0.008 | 2–3 flute carbide |
| Face milling (finishing) | 350–450 | 0.002–0.004 | 2–3 flute carbide, sharp |
| Slot milling | 200–300 | 0.003–0.005 | 2 flute carbide |
| Profile / contour | 300–400 | 0.003–0.005 | 2–3 flute, positive helix |
Climb milling is preferred over conventional milling for Ertalyte. Climb milling begins each chip at maximum thickness and exits thin, which reduces cutting temperature and produces a better surface finish. Conventional milling creates a rubbing action that generates heat and can cause the chip to weld momentarily to the tool.
Use air blast or light misting coolant to clear chips — chip re-cutting degrades surface finish and tool life. Flood coolant is not required for Ertalyte but is acceptable if present for other operations.
Drilling Parameters
| Hole Diameter | Surface Speed (SFM) | Feed (IPR) | Drill Type |
|---|---|---|---|
| <0.250" | 250–350 | 0.003–0.005 | Standard parabolic flute carbide |
| 0.250"–0.750" | 200–280 | 0.005–0.008 | Parabolic flute, 135° split point |
| 0.750"–2.0" | 150–250 | 0.008–0.012 | Parabolic flute, through coolant preferred |
Drilling Notes
- Parabolic flute drills are strongly preferred. The wider flute channel and polished surface evacuate the long Ertalyte chips effectively, reducing the risk of chip packing and bit binding.
- Peck drilling: For holes deeper than 3× diameter, program peck cycles to break and clear chips. Full-depth passes without pecking will pack chips in the flute and cause drill binding, particularly in deep holes in rod stock.
- Coolant: Air blast is sufficient for shallow holes. Through-coolant or peck cycles with flood coolant for holes >2× diameter or tight-tolerance bores.
- Reaming: Ertalyte drilled holes are typically 0.003"–0.005" oversize. Ream for H7 bearing fits. Standard HSS chucking reamers work well; carbide reamers extend life in production quantities.
- Thread tapping: Spiral flute (gun) taps are recommended. Cutting oil or tapping fluid should be applied. Standard tapped threads in Ertalyte — 75% thread engagement — hold pull-out loads well. For critical threads (>0.500" diameter), Helicoil inserts add strength.
Machining Ertalyte TX vs. Natural Ertalyte
Ertalyte TX (PTFE + solid lubricant) machines very similarly to the unfilled grade with a few differences:
- Tool wear: PTFE itself is non-abrasive, but the solid lubricant additive (MoS₂ or graphite) can slightly reduce tool life. Expect 15–25% shorter tool life at the same cutting parameters.
- Chip character: TX chips are slightly shorter and more manageable than natural Ertalyte. The internal lubricant reduces chip weld-on tendency.
- Surface finish: TX achieves slightly lower surface roughness than natural Ertalyte due to the internal lubricant — Ra values below 16 µin (0.4 µm) are achievable in finish turning.
- Tolerances: Same as natural Ertalyte — TX holds ±0.001" on CNC lathe without difficulty.
Workholding and Setup Considerations
Clamping Pressure
Excessive chuck pressure on thin-wall Ertalyte tube or ring sections can deform the bore during turning, causing parts to spring out-of-round after unclamping. Use soft jaws or a collet whenever possible for thin-wall workpieces. For tube with wall thickness less than 0.125", support the bore with an expanding arbor or mandrel.
Stress Relief
Unlike crystalline polymers with high residual stress (some nylon grades, PEEK from certain lots), Ertalyte rod and sheet as produced by reputable suppliers carries low residual stress and does not typically require annealing before precision machining. If dimensional instability is observed in precision parts, a mild anneal at 200°F (93°C) for 2–4 hours in an oven (not forced air) will relieve any residual stress without degrading properties.
Coolant Compatibility
Standard flood coolant (water-soluble), light oil mist, and air blast are all compatible with Ertalyte. Avoid chlorinated cutting fluids — Ertalyte's chemical resistance to chlorinated compounds is limited, and prolonged coolant residue in machined bores can cause surface crazing.
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