Thin-Wall Filament Wound Tubes: Specifying Walls Below 0.5 mm
Engineer's Guide · 2026-09-16 · 5 min read
Thin-wall composite tube is where the process stops being a sourcing decision and becomes an engineering one. Below roughly half a millimetre of wall, the tube is no longer a stiff pipe with an insulating function. It is a shell, and every property that matters is set by the winding, the mandrel and the machining, not by the resin data sheet. This is what to fix on the drawing before you ask for a price.
Where the floor actually sits
There is no single minimum wall figure, because the achievable wall depends on the diameter. A smaller circumference has less of itself to support, so a micro diameter can hold a thinner wall than a large bore. Our own published capability runs from around 0.2 mm on micro diameters, with the practical floor rising as the bore and the strength duty grow. Ask for a wall at your bore, not for a wall in general.
| Bore regime | Wall capability | What the limit is |
|---|---|---|
| Micro diameters | From around 0.2 mm | Mandrel handling and removal, then machining support |
| Small diameters | Around 0.5 mm and up | Roundness retention while the wall cures |
| Medium bores | Thicker again, and set by the strength duty | Hoop stress and the handling load during assembly |
| Large bores | Set by the load case | A large circumference and a high load both need more section |
Six inputs the drawing has to state
- Inner diameter with tolerance, or outside diameter with tolerance. Decide which one is functional, because the other one floats by the wall.
- Wall thickness, stated as a nominal with a band. On a thin section the band is the capability, so state what you can accept rather than what looks tidy.
- Concentricity as a maximum wall variation. This is the number that governs whether a part that has to slide inside a close-fitting bore actually will.
- Length with tolerance, plus end-squareness, plus the cut or the machining required at each end.
- Environment: continuous temperature, peaks, any cryogenic exposure and any chemical contact. The epoxy grade follows from this.
- Load case: what the tube carries in hoop and in column, and how the assembly loads it during fitting. Thin walls fail at assembly more often than in service.
Why filament winding holds the tolerance
Filament winding lays continuous resin-impregnated glass rovings onto a rotating mandrel at a controlled angle under controlled tension. The fibre runs unbroken along the length. That gives the highest hoop strength for a given wall, uniform wall around the circumference, and concentricity tight enough to matter when a part slides inside a close-fitting bore.
- The mandrel sets the bore directly, so the bore is accurate by construction rather than by machining after the fact.
- The fibre is continuous, which is why the burst and hoop performance is better than a rolled tube of the same wall.
- The winding angle sets the strength direction, so the fibre can be placed where the load is instead of evenly and wastefully.
- Cure is where roundness is won or lost, so the process control that matters is the cure, not the resin bag.
The three ways a thin wall fails
| Failure | Where it starts | What prevents it |
|---|---|---|
| Delamination at the machined end | A tool that rubs instead of shearing, on a section with little material to absorb the error | Sharp tooling, proper support, controlled feed, and a deburr that removes lifted fibre |
| Loss of roundness | Cure and mandrel support, and handling before the part is fully cured | Process control at cure and support through every subsequent operation |
| Deformation at assembly | Press or clamp load applied to an unsupported wall | State the assembly load, and design a support or a shoulder into the part rather than relying on the wall |
Machining a thin wall without ruining it
Most of the thin-wall problems we get asked about are machining problems rather than material problems. Composite delamination starts when the cutting edge rubs instead of shearing. On a thin wall there is very little material to absorb that mistake, and the damage does not always show until the part is in service.
- Use sharp tooling and change it on a schedule rather than on failure. A worn edge rubs, and rubbing is what delaminates.
- Support the bore during machining. An unsupported thin wall deflects away from the tool and the cut goes out of tolerance.
- Control feed and speed together. A slow feed with a high speed generates heat at the cut and softens the resin.
- Deburr deliberately and inspect the edge for lifted glass. A lifted fibre is a start point for tracking and a handling hazard.
- Measure the bore and the end-squareness after machining, because those are the two dimensions the assembly depends on.
Where the process is the wrong choice
If the wall is not thin and the tolerance is not tight, a rolled or a pultruded tube is cheaper and good enough. Filament winding earns its cost when concentricity, thin-wall capability or burst strength is the actual requirement rather than a habit. The process comparison is worth reading once before a drawing is released, because the two routes have different cost structures and different lead times.
Where it fits in the wider build: our thin-wall filament wound micro tube route gathers every part that goes into it.
Products for this job
These are the wound tubes we run, from thin-wall micro tube up to larger load cases. Send the part and the equipment you recover with, and we will confirm the size and the profile against them.
Related reading
- Out-of-Round Tubes and End Delamination
- Filament Wound vs Pultruded Fiberglass Tube
- Filament Wound Tube Suppliers
- G10 vs FR-4 Epoxy Fiberglass
Common questions
How thin can a filament wound tube wall go?
It depends on the diameter. Our published capability starts at around 0.2 mm on micro diameters, and the practical floor rises as the bore and the strength duty increase, because a larger circumference and a higher load both need more section. Send the drawing and we confirm the achievable wall for your size.
Why does the minimum wall change with diameter?
A smaller circumference has less material to support and less hoop stress to carry at the same pressure, so a thinner wall remains stable. As the bore grows, roundness during cure and hoop load during service both push the minimum wall up.
What tolerance can a wound tube hold?
Close inner and outer diameter with controlled concentricity, which is the reason the process exists. The exact figure follows your diameter and wall rather than a single published number, so state the dimension that is functional and we confirm the band.
How should I specify concentricity?
As a maximum wall variation, which is a form an inspector can measure with a wall gauge or by sectioning. Stating a concentricity ratio leaves the measurement open to interpretation, and on a thin wall the interpretation is where the argument happens.
Why do thin walls delaminate at the end?
Because the cutting edge rubbed instead of shearing. On a thin section there is very little material to absorb the error, so the damage goes straight into the laminate. Sharp tooling, bore support and a controlled feed prevent it.
Can the ends be threaded or slotted?
Yes, within the limits of the remaining wall. State the feature depth, the edge distance and the remaining section, because a thread in a thin wall removes material exactly where the load concentrates. We confirm the feature against the remaining wall on the drawing.
Which resin grade?
It follows from the environment. Our wound epoxy glass tube runs in epoxy service typically from minus 50 C to plus 130 C, grade dependent, and the engineered range is quoted as class F to H up to around 155 C to 180 C with dielectric strength above 14 kV/mm through the thickness. Tell us the temperature and any flame class.
How do I get a thin-wall tube quoted?
Send the inner and outer diameter, the wall with its band, concentricity as a wall variation, the length, end-squareness, the machining required, the load case and the environment. WELLELE makes filament wound epoxy fiberglass tube with thin-wall capability from around 0.2 mm at micro diameters, close ID and OD, controlled concentricity and machined ends that are deburred and checked.
Specifying this part?
Send the drawing for a manufacturability review.