What is thread tearing at the exit?
Thread tearing at the exit occurs when the chip, not properly evacuated, accumulates in the final part of the hole and is dragged out by the tap during retraction. This causes deformation of the thread in the final turns, resulting in loss of quality, strength and compliance.
The defect is particularly common in deep blind holes, where the chip has no space to move and tends to compact.
Signs that indicate thread tearing at the exit
- damaged or irregular thread in the final turns;
- compacted chip in the final area of the hole;
- tap “jams” in the final millimeters;
- thread surface is dull or torn at the exit;
- screw enters correctly but does not complete tightening;
- abnormal noises in the final stage of tapping.
Why thread tearing at the exit occurs: the main technical causes
Thread tearing at the exit is almost always linked to insufficient chip evacuation in the final part of the hole. The most common causes include:
- Deep blind holes, where the chip has no space to move.
- Long and continuous chip, typical of mild steels, stainless steels and tough alloys.
- Tap geometry unsuitable for blind holes or difficult materials.
- Cutting speed too high, which increases heat and chip compaction.
- Insufficient lubrication, which does not facilitate chip flow.
UFS solutions to eliminate thread tearing at the exit
To prevent thread tearing at the exit, it is essential to use tools designed to improve chip evacuation and optimize cutting parameters. The most effective UFS solutions include:
- Use taps with a pronounced helix, such as the E60+ and K80 series, which promote upward chip extraction.
- Choose chip-breaking taps to fragment the chip and reduce the risk of compaction.
- Reduce cutting speed in the final stage of tapping.
- Improve lubrication to facilitate chip flow.
- Check the usable hole depth to ensure sufficient space for chip accumulation.
Best practices to prevent thread tearing at the exit
- prefer high-helix geometries in blind holes;
- monitor chip shape during machining;
- avoid cutting speeds that are too high on tough materials;
- ensure constant and adequate lubrication;
- choose taps designed for optimal chip evacuation;
- check hole depth before tapping.