What This Collection Does for Your Rotary Assembly This is a line of torsion springs engineered for copper buckle shafts—the small rotating components that control snap-fit closures, latch mechanisms,
This is a line of torsion springs engineered for copper buckle shafts—the small rotating components that control snap-fit closures, latch mechanisms, and spring-loaded hinges. Each spring is wound from 0.3 mm to 4.0 mm diameter wire, heat-treated to 45 HRC, and ground flat on both end legs to within ±0.01 mm of your print. You get consistent torque output across 10,000 cycles because we control coil spacing with CNC coiling machines, not manual winders. From drawing approval to your dock, standard lead time is 10 working days. No MOQ—order one prototype or 50,000 production pieces.
Copper buckle shafts are short, often under 20 mm, and they rotate against a mating housing. A generic torsion spring will twist out of plane, causing side thrust that wears the shaft bore. Our springs use a closed-ground end configuration where the last coil is flattened and squared to 90° ±1°, keeping the spring perpendicular to the shaft axis. This eliminates axial runout. We also control the inner diameter to a H7 fit (for example, 6 mm +0.012 / -0) so the spring seats firmly on the shaft without play. Measured runout on a mandrel is below 0.05 mm, which is why these springs do not need secondary shimming.
We stock three wire grades for this collection: oil-tempered chrome silicon (ASTM A401), stainless steel 302 (ASTM A313), and phosphor bronze (ASTM B159) for corrosion-resistant applications. Each coil is stress-relieved at 260°C for 30 minutes after winding, then shot-peened to 0.25 mm intensity to remove micro-cracks. Chrome silicon springs reach 45–50 HRC, while stainless 302 is drawn to 42–47 HRC. We do not use zinc plating on copper shaft springs—the coating changes the coil friction coefficient. Instead, we offer electropolishing for a 0.2 µm Ra surface finish, which reduces wear against the shaft.
Every batch of 100 springs is torque-tested at three deflection angles: 30°, 60°, and 90°. We use a digital torsion tester with a resolution of 0.001 N·m. For a typical spring with a 10 mm outer diameter and 0.8 mm wire, the torque at 90° is 0.15 N·m ±5%. We also run a 10,000-cycle fatigue test on the first article from each production run. The spring must show less than 3% torque loss after cycling. If it fails, we rewind the entire batch. This is why our springs survive 100,000 cycles in high-end automotive latches—we test what we ship.
Raw springs have a 1.6 µm Ra surface from the wire drawing process. That is fine for enclosed mechanisms, but for exposed copper buckle shafts, we recommend a micro-peened finish at 0.8 µm Ra. This reduces friction when the spring leg slides against the shaft. If you need electrical conductivity, we offer silver-plated springs (5 µm thickness) on the end legs only—the coil body remains bare to avoid welding. For salt spray resistance, passivate stainless 302 to ASTM A967, achieving 48 hours neutral salt spray without red rust.
Your print may call for straight torsion legs, hooked ends, or a double-torsion design with two spring bodies wound in opposite directions. We support all these without extra tooling cost. Leg length tolerance is ±0.5 mm, leg angle tolerance is ±2°, and we can add a pre-set bend at the leg tip to hook into a slot. For automated assembly, we offer taped-and-reeled packaging with 500 springs per reel, so your pick-and-place machine feeds them continuously. We also add a light oil coating (ISO 3448 VG10) to prevent rust during storage—but we skip this if you specify dry springs.
Each spring is checked with a profile projector at 20× magnification for coil diameter, free length, and leg position. We measure hardness on a Rockwell tester (HRC scale) at three points along the coil. For critical orders, we run a scanning electron microscope check on the wire surface to confirm no laps or seams. The final inspection report includes a CMM check for inner diameter and a torque curve graph. You get this report with every shipment, even for a single prototype. If any dimension is outside your tolerance, we reject the part—we do not ship “close enough” springs.
| Parameter | Specification | Notes |
|---|---|---|
| Wire diameter range | 0.3 mm – 4.0 mm | Chrome silicon, 302 SS, phosphor bronze |
| Outer diameter tolerance | ±0.05 mm | Measured on unloaded coil |
| Inner diameter fit | H7 (e.g., 6 mm +0.012 / -0) | For copper buckle shaft seating |
| Free length tolerance | ±0.3 mm | For springs under 50 mm total length |
| Hardness (chrome silicon) | 45 – 50 HRC | Oil-tempered and shot-peened |
| Hardness (stainless 302) | 42 – 47 HRC | Cold-drawn wire |
| Surface finish (raw) | 1.6 µm Ra | As-wound |
| Surface finish (micro-peened) | 0.8 µm Ra | For exposed copper shaft contact |
| Torque tolerance at 90° | ±5% | Example: 0.15 N·m ±0.0075 |
| Axial runout on mandrel | ≤0.05 mm | Tested with 6 mm mandrel |
| Lead time | 10 working days | From drawing approval, prototype or bulk |
| MOQ | No minimum | Start with 1 piece |
Send us your drawing in STEP or PDF, but if you only have a sample, mail it to our Dongguan factory—we reverse-engineer it within 48 hours. Include the shaft diameter, free angle, maximum deflection angle, and required torque at that angle. If you are unsure about torque, tell us the application (e.g., latch for a 2 kg door), and we will calculate the spring rate using our in-house design software. For reference, our CNC cutting tool selection guide explains how tool geometry affects spring winding, and our CNC machining tolerances guide covers what ±0.01 mm means in practice for mating parts.
There is no MOQ—we make a single prototype for you to test, or we run 50,000 pieces at the same per-unit setup cost.
Yes, we custom-wind any wire diameter from 0.3 mm to 4.0 mm, any number of coils, and any leg shape—just send your drawing or a physical sample.
We torque-test three angles per 100-piece batch and run a 10,000-cycle fatigue test on the first article; if torque loss exceeds 3%, we rewind the whole batch.
Standard is 10 working days, but for a spring under 20 mm outer diameter with no heat treatment, we can ship in 5 working days.
Send your drawing to sc@bquq.com or WhatsApp +86 13713157787. We reply with a firm quote within 12 hours—including torque calculation, tolerance confirmation, and delivery date. No MOQ, no engineering fee for standard reviews. Precision manufacturing, made in China, backed by 20 years of spring and CNC experience.
| Parameter | Capability |
|---|---|
| Materials | SUS302/304/316, SWC piano wire, SWP music wire, 65Mn, phosphor bronze, beryllium copper |
| Types | Compression, extension, torsion, wire forms, battery springs, touch springs |
| Wire Diameter | 0.05 - 12.0 mm |
| Tolerance | ±0.02mm standard, ±0.01mm on request |
| Surface | Zinc plating, nickel, black oxide, passivation, shot peening |
| Machines | CNC spring coiling machines, torsion machines, wire forming machines |
| Prototype | 72 hours, no MOQ on samples |
| Inspection | Load test per batch, fatigue test data on request |
