Moreover, the external fixator strut clamp body is the locking node of an external fixator frame. It grips the carbon fibre or stainless strut at one end and the Schanz pin or half pin at the other. It has to hold that grip while the frame is loaded by patient movement and by the surgeon’s reduction manoeuvres. Fab-welded clamp bodies distort at the weld, so the strut and pin bores end up out of parallel and the clamp creeps once the frame is tensioned. Solid-machined bodies avoid the weld but waste most of the billet and leave a sharp step where the two bores meet. A one-piece investment casting puts both bores, the clamp split and the tightening lug in the same body, then gets finish machined after H900 aging so the two axes stay parallel to the drawing.
Specifications
| Parameter | Specification |
|---|---|
| Casting process | Silica sol lost wax investment casting; water glass route offered for non-critical cosmetic bodies |
| Material options | 17-4PH (H900 primary / H1025 optional), AISI 316L for the pin bushing and clamp insert |
| Dimensional tolerance (ISO 8062-3 CT grade) | CT5 as cast; CT4 on the strut bore, pin bore and clamp datum faces after machining |
| Machining | 4-axis and 5-axis CNC milling, CNC turning of the bores, reaming of the pin seat, slotting of the clamp split |
| Surface finish (Ra) | Ra 1.6 um machined; Ra 0.4 um electropolished on request; Ra 3.2 um bead blasted matte |
| Weight range | 45 g to 220 g per clamp body depending on strut diameter and pin size |
| Typical lead time | Tooling 4-5 weeks; first article 2-3 weeks after tooling; production 5-7 weeks |
Key features
- One-piece cast body removes the weld and post-weld straightening operation, holding the strut and pin bores parallel within +/-0.04 mm over a 60 mm clamp length.
- Both bores are finish reamed after H900 aging, so the clamp grips without the bore ovality that lets a pin rotate under frame load.
- H900 condition delivers 38-42 HRC at the clamp split and tightening lug faces, resisting the wear that loosens the screw over repeated frame adjustments.
- Cast clamp split with a radiused root removes the sharp machined corner where crack initiation starts in solid-machined clamp jaws.
- Uniform wall section through the lug-to-body junction prevents the sink and shrinkage porosity that appears in thick weld-built clamp corners, verified by X-ray sampling.
- Cast-in size identification pad and torque reference mark are laser marked after passivation for legible identification after hospital sterilization cycles.
- AISI 316L insert or bushing option isolates dissimilar metals at the carbon fibre strut interface to limit galvanic corrosion in long-dwelling frames.
Applications
- Ring and hybrid external fixator frames for open tibial and femoral fracture management.
- Moreover, Monolateral and unilateral fixator clamp bodies in limb lengthening and deformity correction systems.
- Generally, Pin-to-bar and bar-to-bar coupling clamps in trauma damage control frames.
- Pelvic and periarticular external fixation sets used in polytrauma cases.
- Paediatric and small bone fixator frames built on scaled clamp geometry.
- Additionally, Veterinary external fixator clamp bodies for small and large animal orthopaedics.
Quality & compliance
Ningbo Ruican is not an ISO 13485 contract manufacturer. It supplies cast and CNC-machined components in 17-4PH (H900/H1025), AISI 420 and AISI 316L together with project-level documentation under the customer’s Quality Agreement, including material traceability and ISO 10993-5 biocompatibility test support. Each clamp body release ships with EN 10204 3.1 material certification, heat lot records, furnace charts from solution treatment and aging, a hardness survey across the lug and clamp split, and dimensional reports generated against the approved drawing. Process control records, non-conformance handling and change control follow the customer’s documented requirements rather than a claimed device QMS registration.
FAQ
Can you work from an existing clamp sample rather than a drawing?
Yes. Send a sample clamp body plus the strut and pin sizes it must accept, and we reverse scan the part, rebuild it as a 3D model, and return that model with a DFM review covering gating, draft, machining allowance and bore tolerance. Production starts only after you approve the rebuilt model and the first article inspection report.
What is the minimum order for a new clamp design?
There is no fixed minimum. We build one tooling set and supply prototype and pilot quantities from it, then move to multi-cavity tooling once your annual volume justifies the investment. Also, tooling is maintained and stored for repeat orders, and we can hold agreed safety stock against a released schedule.
Which documentation ships with the first article?
The first article ships with a dimensional report against every ballooned feature, EN 10204 3.1 material certificate, heat lot record, solution treatment and aging furnace charts, a hardness survey, surface finish measurement and photographs. Production lots repeat the package at the sampling intensity agreed in the Quality Agreement.
Can you hold H900 hardness consistently across the clamp body?
We age in a calibrated furnace with load thermocouples, then survey hardness at the lug, clamp split and body as agreed on the drawing. H900 typically lands at 38-42 HRC, and any out-of-window result is quarantined, dispositioned and reported through the customer’s non-conformance route rather than silently re-tested.
Do you passivate or electropolish fixator clamp bodies?
Both. Standard supply is passivation per ASTM A967 after final machining, with optional electropolishing to Ra 0.4 um where a smoother cleanable surface is specified. Bead blasting to Ra 3.2 um is available for a matte finish, and marking is applied last so it survives sterilization.
CTA
Send your external fixator strut clamp drawing, sample or 3D model for a DFM review and a tooling plus piece price quotation. Contact Wendy She — sales@cnsandcasting.com — WhatsApp +86-13777124360, or visit https://cnsandcasting.com to start your orthopaedic trauma casting program with Ningbo Ruican.
