Dig-in is the failure where a turn sinks into the layer beneath it and the spool stops giving up product cleanly. The operator sees a sudden increase in tension, then a jerk, then either a jam or a length of product that has been stretched or marked. It is one of the most common winding faults and one of the most preventable.
How it happens
Turns in a layer sit side by side. If a gap opens between them, the turn in the next layer can drop into it. Once it has dropped in, it is wedged: to come out, it has to climb back over the turn beside it, and that takes more force than the payoff provides.
The result is a sudden resistance, a spike in tension, and either a break or a jerk that damages the product even if it does not break it.
The usual causes
- Traverse pitch too wide. Gaps between turns are an open invitation. This is the most common cause by a distance.
- Tension too low during winding. A slack layer is not held in place and shifts under the pressure of the layers above.
- Soft or compressible product. A jacket that deforms under pressure will settle into gaps that a stiffer product would bridge.
- Too many layers. The inner layers carry the accumulated pressure of everything wound on top, so deep packs are more prone to it.
- Tension falling off near the end of the wind. The last layers are the loosest and the most likely to have been wound with the winder slowing down.
Early warning signs
You can often see it before it causes a jam. Look at the surface of a finished pack: if you can see a regular pattern of depressions, or if the outer layer is not flat, the layers beneath are probably not either. Run a fingernail across the pack — a bumpy or ridged surface means the wind is not laying flat.
A second sign is a periodic tension variation at the frequency of turns rather than once per revolution. That is a different signature from unbalance, and it points at the wind rather than the spool.
Preventing it
- Tighten the pitch so turns sit close together without riding up. This is a setting, not a purchase.
- Hold tension constant through the wind, including at the end. Most winders reduce tension as the pack builds; some reduce it too far.
- Use a taper tension profile if the product is soft — slightly higher tension at the start, easing off, gives a firm base without crushing the inner layers.
- Limit layer count for soft product. A wider spool with fewer layers is kinder than a narrow one with many.
Interlayer separation
For genuinely soft or sticky product, an interlayer sheet — a thin film or paper wound between layers — prevents one layer bonding to or embedding in the next. It works, and it costs money and handling time, so it tends to be reserved for product where the alternative is worse.
Where it is used, the sheet has to be wider than the pack and it has to be removed cleanly at payoff, which means a take-up reel. That is a real capital item, and it is worth pricing before deciding that interlayer is the answer.
When it is the spool
Occasionally dig-in is caused by the spool rather than the wind: a core that is slightly undersized lets the first layer sink, or a flange that flexes inward under tension pinches the pack at the edges. If the same wind runs fine on one spool and not another, check the core diameter and the flange deflection before touching the winder.
Send us the product, the tension and the spool dimensions and we can usually tell you which of the causes is most likely before you spend a shift on trial and error.