What’s causing the thread to break?
Q Why does the thread snap when I am tying off flies with a whip finish? Is the hook to blame? David Todd
PAUL PROCTER REPLIES: Initially, I’d be tempted to say the tension on the feet of your bobbin holder is a little tight, which prevents the thread spool from turning smoothly. However, given that breakages are occurring on completion of the fly, it sounds like one of the two following problems. The most likely cause is that during the process of tying a fly, unless you keep it in check, the multi-fibre threads we use will gradually become more tensioned due to twisting. Assuming you’re right-handed, the threads gradually tighten in a clockwise direction with each revolution of the hook shank when viewed from above. This tightening process eventually becomes too much for the thread, causing it to break. Do bear in mind that a fair few turns of thread are required when dressing each fly, so it’s possible to see how this can happen. In extreme cases the thread begins to ‘ball up’ on itself, especially prior to snapping. Because we’re taught to maintain a tight bobbin/thread this ‘balling-up’ effect isn’t always obvious. However, when completing a fly using a whip finish, or series of half hitches, sometimes we inadvertently generate a little slack, which causes the thread to ‘ball-up’. This small tangle of thread cannot possibly pass through the whip finish knot and consequently causes a break. There is good news here, as this is preventable. When dressing a fly, after each stage, like tying in the tail for example, we should periodically and gently spin our bobbin holder in an anticlockwise direction. Such actions release excessive twisting of multi-fibre threads, leaving them in their un-twisted neutral state. We can even gauge this by letting the bobbin holder hang for a few moments, when you’re likely to see it begin rotating in an anticlockwise direction until all the unwanted twists are removed, whereupon it will come to rest. This indicates the thread is now in the desired neutral state. The second issue is sometimes caused by a tiny burr which can occur on the hook eye end during manufacturing process. Or, the eye is not properly closed, resulting in a miniscule gap. Both these faults result in a possible sharp edge that is lethal on taut threads and cuts them like a hot knife through butter. As we tend to initially secure our thread (catch it on) a little way behind the hook eye this burr remains unnoticed until you come to the tying off (whip finish) procedure. Now, the thread is immediately behind the hook eye where it can catch on any sharp edge. As hooks tend to come in batches, if you do experience this it’s best to disregard that certain box/ packet of hooks.
Check hook eyes for gaps or burrs that can snag thread. Thread gradually tightens in a clockwise direction during tying. Periodically and gently spin the bobbin holder in an anticlockwise direction to release excessive twisting.