Linen Phenolic Tube

Linen phenolic tube combines the fine-weave fabric advantage of linen phenolic rod with the ready-to-bore sleeve geometry of tube — enabling precision instrument bearings, fine-pitch coil forms, and high-voltage isolation sleeves that require superior surface finish and tighter wall tolerances than cotton phenolic tube can deliver.

TL;DR — Linen Phenolic Tube Quick Facts

Standard Sizes — Linen Phenolic Tube

Linen phenolic tube is primarily a custom form — ID and OD are specified to the buyer's finished-part requirements. Standard near-stock configurations:

Linen phenolic tube is produced in smaller maximum OD than cotton phenolic due to the finer fabric weave used in the manufacturing process. For ODs above 10" in a phenolic laminate, cotton phenolic tube (NEMA C/CE) is the more available option.

Properties Relevant to Tube Form

Linen phenolic tube is wound or compression-molded with the linen fabric planes running circumferentially in the tube wall, maximizing hoop and compressive strength in the wall. The finer linen fiber versus cotton results in:

• Smoother as-manufactured bore surface
• More consistent wall thickness (fewer laminate gaps)
• Slightly lower impact strength (acceptable trade-off for precision bore work)

Grade L for precision mechanical sleeves and bearing applications. Grade LE for applications requiring voltage isolation — transformer coil forms, insulating sleeves in switchgear, and relay actuator sleeves in live-circuit assemblies.

For the complete datasheet, see Linen Phenolic properties.

Typical Applications — Tube Form

Linen phenolic tube is the preferred form when a ready-to-finish bore geometry, fine surface finish, and tight wall tolerances converge in a single part:

Precision instrument sleeve bearings — Linen phenolic LE tube bored to Class 2 bearing fits (H7 tolerance) for instrument pivots, galvanometer frames, and scientific apparatus bearings where stick-slip motion from surface roughness would corrupt measurement. The finer linen weave delivers bore Ra 16 μin after boring — comparable to honed steel but without metal contamination risk.

Transformer coil forms (bobbin tubes) — Grade LE tube as winding forms for small power transformers and toroidal chokes. The tube provides structural rigidity to support wire winding tension, thermal resistance to handle core losses, and electrical isolation between the winding and any grounded core material.

Precision electrical isolating sleeves — Cut tube sections as sleeves over bus bar bolts, machine screws, and fasteners connecting live components in switchgear, motor control centers, and relay panels; Grade LE at 250+ V/mil wall dielectric strength supports medium-voltage isolation.

Antenna coil formers — Linen phenolic LE tube as the coil former for variable inductors and RF coils in laboratory and industrial measurement equipment where the lower dissipation factor versus cotton phenolic improves Q factor at radio frequencies.

Aircraft instrument components — To MIL-I-24768/13 (Type FBG-LE), linen phenolic LE tube is specified in avionics instrument gimbals and actuator sleeves where electrical isolation and precision dimensional stability under vibration and temperature cycling are required.

Precision spacers in electronic chassis — Cut-to-length tube sections as PCB standoffs and chassis spacers in electronic racks where accurate board-to-board spacing (±0.005") and electrical isolation are both required.

Machining Notes — Tube

Linen phenolic tube machines with the same tooling as linen phenolic rod, with additional attention to wall support:

OD turning and wall finishing: Solid-carbide tooling, 400–600 SFM, 0.002–0.004 IPR for finishing passes. Support thin-wall tube (wall below 0.500") with a mandrel or steady rest to prevent chatter and wall collapse under cutting force.

Bore finishing (ID): Boring bar with positive-rake insert; spring-back 0.001"–0.002" after boring. For precision bearing fits, follow boring with honing to 220–320 grit — achieves Ra 8–16 μin in bore. Use a split expanding mandrel on the OD while honing to prevent out-of-round distortion under honing stone pressure.

End face squareness: Face both ends to square and flush. Linen phenolic tube ends can show a slight coned profile from the mandrel winding process; facing removes this and provides a flat datum for length measurement.

Thread tapping (OD threads): Linen phenolic accepts external threads cut by single-point or thread-chasing method; internal threads in the bore are feasible for coarse threads (1/4-20 and larger) in wall thicknesses above 1/4". Use sharp bottoming tap for maximum thread engagement.

Cutting parting: Carbide parting blade, 0.060"–0.100" wide, moderate feed. Support tube close to parting zone. After parting, deburr the inner bore edge with a chamfer tool or 240-grit abrasive cone to remove any fiber fringe at the cut edge.

Dust control: Localized exhaust ventilation, NIOSH P100 respirator required. Linen phenolic dust has similar respiratory hazard profile to cotton phenolic.

See the Linen Phenolic Machining Guide for complete parameters.

Standards and Compliance

Tube is frequently made-to-order; request a Certificate of Conformance citing NEMA LI 1 grade at order entry. For MIL applications, confirm QPL qualification of the tube manufacturer before committing to a procurement.

More related guides

Applications

• Electrical Insulation — Phenolic & Laminate Options
• Bushings & Bearings — Material Selector

Industries

• Aerospace Plastics
• General Industrial Plastics

Compare materials

• Cotton vs. Linen Phenolic
• Linen vs. Canvas Phenolic
• Phenolic Paper vs. Glass Comparison

Other linen phenolic forms

• Linen Phenolic Rod
• Linen Phenolic Sheet