Why does my sewing machine vibrate?

Start with what the machine is standing on, because that is the cause far more often than the machine itself.

The table. A light folding table or a thin desk top flexes and amplifies every stroke of the needle bar. A solid table, or a machine mat, transforms this. Sewing cabinets exist largely for this reason.

The feet. Rubber feet harden and shrink with age, so the machine rocks on three of four. Check it does not rock, and replace perished feet — they are cheap parts.

Speed. Every domestic machine vibrates more at the top of its range. If it is smooth at moderate speed and harsh at full speed, that is normal behaviour rather than a fault.

An unbalanced bobbin. A bobbin wound unevenly, or one that is cracked or warped, spins off-centre and produces a rhythmic buzz that comes and goes as it empties.

Lint packed in the race makes the hook labour, which reads as vibration and noise together.

A loose needle plate or extension table, or an accessory box not clipped in properly, will rattle in sympathy without the machine being at fault at all.

Then the mechanism. A loose belt, a worn bearing or dried grease produces genuine mechanical vibration, usually with a change in the sound as well.

One clear signal to stop. Vibration accompanied by knocking means the needle is striking something, and that is not a vibration problem — stop and check the needle and plate.