Engineering · Manufacturing
Spring Coiling Troubleshooting: Pretension, Diameter, Distortion and Swarf
A symptom-to-cause guide for weak springs, unstable pretension, wobbly bodies, curved springs, excessive swarf, repeated weak points, wire escape and cutting problems on a single-point CNC spring coiler.
Source fidelity and use of values
This handbook page is derived from an anonymised machine-specific operating and setup manual. Numerical settings are retained only where they carry practical technical meaning. They are marked as source examples and are not universal specifications. Machine builders, tooling geometry, wire condition and site safety procedures can require different values.
1. Troubleshoot the forming system, not a single setting
Pretension, diameter, surface quality and straightness are coupled. The source troubleshooting chapter is most useful when read as a set of cause-and-effect relationships. Worn tools change wire retention. Guide pressure changes friction and twist. Coiling-point position changes both pretension and diameter. Feed-roll pressure can bend the incoming wire. A deflector that pushes sideways can create a local bump. Correct diagnosis therefore begins with the visible defect and follows the wire path backward.
2. Lack of pretension
| Potential cause | Mechanism described in source | Diagnostic action |
|---|---|---|
| Worn coiling point or block guide | Groove support is reduced; wire escapes before sufficient twist develops. | Inspect the leading edges and place the guide on a flat surface to reveal wear or loss of land. |
| Block guide too tight | Friction, heat and distortion rise, which can reduce pretension rather than increase it. | Back off in very small steps and check whether swarf and temperature fall. |
| Block guide too loose | Wire control is poor and blank diameter increases; pretension becomes harder to attain. | Increase support incrementally while retaining a sliding/rocking feel. |
| Sharp or poorly finished tool edges | High local friction and wire surface damage interfere with smooth forming. | Inspect tool finish and restore the intended small radius/chamfer without reducing groove depth. |
| Spring coils on tool face rather than on itself | Tool contact acts like unintended pitch and opens the helix. | Check front clearance geometry on the block guide and coiling point. |
| Pitch tool touching the spring | Acts like a pitch-forming tool and separates coils. | Retract or realign the pitch tool so it clears normal body coiling. |
3. Pretension falls during production
If pretension was initially satisfactory and then drops after a tangle or crash, the source first checks for chipped tooling. The block guide is described as relatively tolerant of minor chipping, while the coiling point is much less tolerant: a small chip where the wire passes can noticeably reduce pretension. This is why a process that suddenly changes after an incident should be inspected mechanically before the program is altered.
Also inspect for swarf packed under the block guide or behind the arbor. One source problem case showed that cleaning accumulated swarf restored pretension even when its origin was not immediately visible.
4. Excessive swarf
Swarf is a diagnostic signal. The source links heavy swarf to block-guide clearance that is too tight, incorrectly finished tooling, excessive coiling-point movement and wire misalignment through replacement tooling. If the operator keeps increasing pretension while heavy swarf is forming, the process can enter a damaging feedback loop: friction creates debris, debris further increases friction, surface finish worsens and pretension falls.
Do not treat swarf as normal waste
Fine dust may occur during running-in, but persistent heavy swarf indicates that the wire is rubbing or being shaved. Correct alignment and surface finish before continuing production.
5. Weak first coils
A spring can have acceptable pretension through most of its length but remain weak at the first few coils. The source identifies a worn coiling-point leading edge as a major cause. The worn edge reduces effective groove depth so the wire climbs out early. A useful observation is the direction of the spring as it exits the tool: if the start travels upward instead of close to horizontal, the wire may be escaping the groove prematurely.
Possible corrections in the source include restoring or replacing the coiling-point tool, moving the diameter tool slightly inward so the wire is forced more deeply into the groove, and in some setups trying the next larger coiling-point groove. Any inward movement must be small because too much can increase diameter and reduce pretension.
6. Wobbly or distorted spring body
A wobbly spring usually indicates that the wire is not following a stable circular path around the arbor. The source identifies several causes: coiling point too far out so the wire loses firm contact with the arbor cutting edge; coiling point too far in, which over-forms the spring; block guide too tight; insufficient material removed from the front of the guide; or a sharp outside edge that the wire catches as it coils.
The manual notes that a wire catching a sharp guide edge can sometimes be heard as a clicking sound during blank-spring generation. This makes sound a useful process observation. A repeating click at the same point in every revolution can reveal a tool edge that is not obvious from visual inspection.
7. Curved spring
A spring that is straight in coil spacing but bends like a bow can be caused by the diameter tool being set too far in, excessive feed-roll pressure, or an over-tight block guide. Excess feed pressure is particularly important because it changes the condition of the wire before forming. The source recommends only enough pressure to prevent slip; one example uses approximately 300 lbf entry and 350 lbf exit on 1.12 mm wire.
8. Bump near the front of the spring
A local bump near the hook can be created when the hook catches a gap between the guide bracket and guide plate in the ejector area. The source recommends minimising the catch point at the guide bend. A second cause is spring diameter that is not at the minimum stable setting: when the spring contacts the deflector, the loose geometry can buckle locally.
Sideways adjustment of the ejector ramp also matters. Pushing the spring down into the ramp can be acceptable, but a strong sideways deflection as the spring exits the arbor can produce a bump. The source later updated the setup to position the ramp so the spring is already touching the ramp as it leaves the arbor, reducing the lateral impact.
9. Irregular coil spacing at the front
If the spring guide bracket is bent upward, the spring can climb out of the ramp and create a local gap between coils. Bending the guide downward helps the spring climb into the ramp, but too much downward angle can prevent reliable ejection. The correct position is therefore a compromise between guidance and discharge.
10. Wire pushed out of the block guide
Thinner wire can sometimes be forced sideways out of the block guide. The source uses the pitch tool underneath the guide as additional support. The pitch tool must not be advanced so far that it contacts the spring body and acts like a pitch-forming element, because that would reduce pretension.
11. Spring noisy in the ejector
A rattling spring can indicate that the hook leg is not parallel with the spring body. As the spring rotates in the ramp, the hook protrudes and strikes the chute, potentially introducing waviness and even reducing pretension. Correct hook perpendicularity before modifying the ramp or slowing the machine.
12. Equally spaced weak points
The source describes cyclic weak regions at roughly 12 mm spacing and links the spacing to one revolution of a feed roll. That is a powerful diagnostic method: if a defect repeats at a fixed pitch, compare the pitch with the circumference of rotating components in the wire path. The source’s normal cause is a loose or broken spring/component in the feed-roll assembly.
The exact 12 mm spacing is machine-specific. The general rule is to use defect periodicity to identify the rotating element responsible.
13. Wire jumps out of the coiling-point tool
If the wire suddenly escapes the coiling-point groove, the force required to drive it around the arbor may be too high. The source suggests reducing the coiling-point pressure, reducing the programmed pretension value and polishing the tool with fine diamond compound to lower friction. Before reducing process capability, however, inspect the guide for over-tightness and the tool for rough or damaged surfaces.
14. Problem-solving case: many changes, one damaged edge
One source investigation changed arbor size, arbor relief, coiling-point size, guide tightness and wire coil while trying to recover pretension. The key observations were that a looser guide significantly improved pretension, swarf accumulation reduced pretension, and the coiling-point tool had a small chip in the leading edge. The operator ultimately altered torsion so the wire path missed the chipped region. The case illustrates why visual tool inspection should be early in the troubleshooting sequence.
15. Problem-solving case: replacement tool alignment
Another case followed a broken block guide that was replaced by a locally made part. Pretension was difficult and swarf was heavy despite grinding and polishing. The successful correction was a small change to arbor axial position. The replacement guide’s groove sat slightly differently, so the wire no longer aligned correctly from the upstream guide into the forming zone. Moving the arbor restored alignment, eliminated swarf and allowed good pretension at a lower coiling-point setting.
16. Structured troubleshooting order
- Confirm the defect on more than one part and note where it begins.
- Check whether the problem appeared after a tangle, crash, tool change, wire change or zero reset.
- Inspect coiling point, block guide and arbor for chips, sharp edges, wear and swarf.
- Generate a blank spring and check horizontal exit and minimum stable diameter.
- Check block-guide sliding fit and feed-roll pressure.
- Check wire alignment and straightening.
- Only then change pretension, diameter or torsion program values one at a time.
- Revalidate at production speed and record the successful correction.