Machining for medical and dental hardware
Medical work is less about exotic tolerance and more about evidence: the right material grade, a surface that can be cleaned, edges that will not cut a glove, and a record that survives an audit two years later.
Part families
Handles, forceps bodies and instrument shafts in 17-4 PH, 420 or 440C. The critical features are flatness on the mating faces, pivot hole alignment, and an edge break that is comfortable in a gloved hand.
Aluminium or stainless enclosures with gasket grooves, display windows and connector cutouts, finished by anodizing or passivation. Cosmetic faces are agreed on the drawing rather than argued at incoming inspection.
Implant-adjacent parts, abutment holders, model components and prosthetic hardware. Small features, tight position tolerances, and a surface finish that will not trap residue.
Manifolds, valve bodies and connectors with intersecting passages and O-ring grooves. Burr at a passage intersection is a contamination risk, so deburr is a process step with a check, not a courtesy.
Go/no-go gauges, holding fixtures and microfluidic test blocks. These parts are the measurement system, so their tolerance is tighter than the part they check.
Material and finish logic
| Requirement | Material | Finish | Note |
|---|---|---|---|
| Corrosion plus strength | 17-4 PH (630) | Passivation | H900 or H1025 condition |
| Cutting edges, wear | 440C | Passivation, polish | Hardened after machining, ground after |
| Chemical resistance | 316L | Passivation, electropolish | Low carbon for welded assemblies |
| Lightweight housing | 6061-T6 | Anodize | Not for repeated autoclave cycles |
| Insulation and wear | PEEK, PTFE | None | Stress relief between rough and finish |
| Biocompatible metal | Ti Gr2 / TC4 | Passivation | Mill cert per heat lot |
Cleanability starts at the drawing
A part with a blind 1.5 mm groove, a sharp internal corner and a cross-drilled hole breaking into it cannot be cleaned reliably, whatever the surface finish. Residue collects in geometry, and geometry is a design decision.
Practical rules: give every internal corner a radius of at least a third of the groove width, avoid blind holes intersecting passages at acute angles, and specify Ra 0.8 µm or better on any surface contacting tissue, drug product or cleaning fluid.
| Edge break | 0.2–0.5 mm on handled edges, stated on the drawing |
|---|---|
| Internal radii | ≥ 1 mm, ideally ≥ 0.5 × feature width |
| Blind holes | Depth ≤ 4 × diameter, or through-drilled |
| Surface finish | Ra 0.8 µm functional, Ra 0.4 µm fluid contact |
| Marking | Laser engraving, away from contact surfaces |
Documentation we supply
Mill certificate with grade, heat number, chemistry and mechanical properties, matched to the batch. For 17-4 PH the condition is stated, because H900 and H1025 machine and perform differently.
The callouts that affect function, measured on a CMM with the drawing's datum scheme. Bubbled drawing numbers make it reviewable in minutes.
Issued against the batch, covering the material and the finish chemistry. Useful when the finished device has its own declaration obligation.
Industry questions
Yes, and we recommend it. Send the NDA first, then the model. Design files stay with the programme and are not used for any other customer.
Ti-6Al-4V (TC4) is available with mill certification. Machining is slower than aluminium and the quote reflects tool wear, so it is worth confirming the grade is genuinely required before specifying.
By process: sharp tooling, controlled final passes, a defined deburr step, and magnification inspection on critical edges. For batches, vibratory finishing followed by edge inspection.
Yes, coordinated with the finishing supplier and quoted with the part. It removes 5–20 µm, so any tolerance on a polished surface must account for that before machining.
Send the drawing with material and finish condition stated.
For medical work, tell us the cleaning cycle and the documentation level early. Both change the process and neither can be added cheaply after the first batch.
From the shop notes
Longer answers to the questions these pages raise.