Cannula & Lumen Work — The Burr Is Inside, and You Cannot See It
Four defects you find by cutting the part open
- Internal burr at a side port. A cross hole into a lumen leaves a burr on the inside wall. It cannot be reached by hand, it traps residue, and it disturbs flow at exactly the point the port was designed for.
- Lumen step at a junction. Two drilled features meeting slightly off-axis leave a step. It measures acceptably at both ends and creates a ledge in the middle.
- Thin-wall deflection. A tube wall deflects away from the drill, so the hole is not round and the wall on the far side is thinner than the drawing. The second effect is the dangerous one.
- Torn tip or edge. The distal tip and any cut window are functional edges. A rolled edge there is both a trauma risk and a cleaning problem, and it cannot be corrected after the geometry has moved.
General small-hole drilling fundamentals — speeds, pecking, runout — are covered on Small-Diameter Holemaking. This page assumes them and addresses what a lumen adds.
What drives tooling on a cannula
| Feature | What usually decides the tool | HENTRY entry |
|---|---|---|
| Main lumen through a shaft | Depth-to-diameter ratio, and whether coolant can reach the bottom | Deep Hole Carbide Drills · Gun Drills |
| Side ports into the lumen | The exit condition on the inner wall, which is the defect you cannot inspect | Micro Carbide Drills |
| Tip and window forms | Whether the geometry can be cut clean at the wall thickness available | Micro End Mills · Custom End Mills |
| Hub and luer interfaces | Taper form and concentricity to the lumen axis | Carbide Reamer · Custom End Mills |
| Hypotube in long coils | Support along the length, because deflection grows with unsupported span | Reviewed per print — support method is part of the quote |
Which alloy pushes you where
| Material | Route | Why |
|---|---|---|
| 316L and 304 stainless tube | Carbide micro drills with a controlled entry | Work hardens; a rubbing entry hardens the wall before the hole is even started |
| Nitinol tube | Sharp geometry, low engagement, expect springback | Superelastic; it moves away from the tool and returns, changing effective depth and burr |
| Ti-6Al-4V tube | Carbide, coolant aimed at the cut, no dwelling | Heat stays at the edge and a pause welds material to the flank |
| PEEK and polymer tube | Sharp single-flute or PCD geometry with a defined exit | Melting and fuzzing at the edge rather than a conventional burr |
| Pt-Ir and precious alloy tube | Reviewed per print | Material cost makes scrap expensive; the process is proved on a coupon first |
Boundaries, so you do not read the wrong page
- Instrument bodies, jaws and edges — mated condition and serrations → Surgical Instrument Machining.
- Screws, plates and threads → Orthopaedic Implant Machining.
- General micro drilling without a device requirement → Small-Diameter Holemaking.
- Deep passages in a solid block rather than a tube — hydraulic galleries → Hydraulic Manifold Drilling.
What makes a cannula quote reviewable
- Tube OD, ID, wall thickness and the tolerance on each
- Lumen depth and the depth-to-diameter ratio, plus whether it is through or blind
- Side-port position, diameter and the inner-wall condition required
- Which edge or window is functional, and what it must not have
- How the tube is supported during machining, and the maximum unsupported span
- Material and condition — 316L, nitinol, Ti-6Al-4V, PEEK — and the cleaning step that follows
Quick answers before you RFQ
How do you control a burr you cannot reach?
By not creating it. The exit condition at a side port is set by the drill geometry, the feed as it breaks through and what is behind the exit — the opposite wall of the tube acts as the support. Where the burr cannot be prevented, the operation is planned so the burr forms on a side that can be reached, which sometimes means changing the drilling direction rather than the tool.
What is the practical limit on lumen depth?
It is set by deflection and chip evacuation together, not by a fixed ratio. A short, stiff drill in a supported tube reaches further than a long one in a free span. That is why the support method is asked for at RFQ stage — the same tool gives different results depending on how the tube is held.
Can nitinol tube be drilled reliably?
Yes, with the behaviour accounted for rather than assumed. Nitinol is superelastic: it moves away from the edge and returns, so the effective depth of cut and the burr differ from stainless at the same setting. The process is set for that and proved on a coupon before a batch is committed.
Where does the general micro-drilling guidance live?
On Small-Diameter Holemaking. That page covers speeds, pecking and runout for small holes in general. This page covers what a lumen and a thin wall add — the inner-wall exit condition and the support question.
Send the tube section and the support method
Primary tooling entries for cannula work: micro carbide drills, deep-hole and gun drills, micro end mills for tip and window forms. Support method and depth ratio are reviewed with the tool, because they change the result more than the geometry does.