Yes, slightly, and on some machines noticeably. As a bobbin empties, the diameter of the remaining thread shrinks, so the thread pays out at a different rate and with a different drag against the case. The last few metres are the worst.
What you see. A seam that was balanced starts to look slightly loose or slightly tight in its final stretch, or the stitch quality wobbles just before the bobbin runs out. On a well made machine the effect is small. On a cheap bobbin case it can be obvious.
The practical rule. Never start a long seam or a run of visible topstitching on a bobbin you cannot see plenty of thread on. Wind a fresh one. Running out mid seam forces a join, which is a weak point and shows.
Two related causes worth ruling out. An unevenly wound bobbin varies its tension from the start rather than only at the end, so wind through the proper guide and let the machine do it rather than winding by hand. And the wrong class of bobbin sits at a slightly wrong height in the case, which produces tension faults throughout.
Bobbins are not universal. Even where two look identical, a fraction of a millimetre in height, or a plastic bobbin in a machine designed for metal, changes how it turns.
If the fault appears at any bobbin level, it is not this. Clean the race and check the case for a thread caught under the spring.
Questions people actually ask
Should I always use a full bobbin?
For long seams and topstitching, yes. For short seams that will be crossed by other seams it makes little difference.
Can I wind over an existing bobbin?
Better not to. The old thread underneath may be a different weight or age, and the wind will be uneven.
Last reviewed 2026-08-11