A machine that was fine and is now not has had something change, and it is usually one of four things.
The needle blunted or was damaged. A needle that hit a pin ten minutes ago may look straight and be burred at the tip. This is the most common answer and the cheapest to test.
Lint reached a threshold. Lint accumulates gradually and then crosses the point where the hook cannot pick the thread up cleanly. It feels sudden because the symptom is sudden even though the cause was not.
The thread reached a bad section, or you started a new spool of poorer thread.
The bobbin ran low. Tension changes as a bobbin empties, because the diameter of the remaining thread changes how it pays out. Some machines are noticeably worse in the last few metres.
The order to check. Change the needle. Re-thread with the foot up. Fit a fresh full bobbin. Clean the race. That is ten minutes and it fixes this fault the large majority of the time.
If it recurs on a schedule — every project, every few hours — that is telling you the machine wants cleaning more often than you are cleaning it.
Questions people actually ask
It only happens on one fabric.
Then it is not sudden, it is fabric-specific. Change to the correct needle type for that fabric and re-test tension.
Could it be the weather?
Humidity genuinely affects some threads, particularly cotton and viscose. It is a real if minor factor, and it is the last thing to suspect.
Last reviewed 2026-08-11