Shredding is a friction fault. The thread is being abraded as it passes through something, and there are only a few candidates.
The needle eye is too small for the thread. This is the most common cause, and it is nearly always topstitch or embroidery thread through a universal needle. Fit a topstitch needle, which has a larger eye and a deeper groove to protect the thread.
The needle is blunt or burred. A burr at the eye acts like a file. Change the needle — it is the fastest thing to rule out.
A burr elsewhere on the thread path. The needle plate around the hole, the bobbin case, or a thread guide. Run the thread slowly through by hand and feel for a catch.
Tension too tight, which increases the force pulling the thread across every surface it touches.
Speed. At high speed the thread passes through the eye many more times per second and heats up, particularly synthetics. If it only shreds when you sew fast, slow down and see.
And old thread. Cotton thread in particular degrades with age and humidity. Pull a length between your hands: if it breaks easily, it will break in the machine.
Questions people actually ask
It only shreds with metallic thread.
Metallic is abrasive and fragile. Use a metallic or topstitch needle, reduce tension, sew slowly, and use a vertical spool pin so the thread unwinds rather than twists.
Should I use thread conditioner?
For hand sewing, yes. In a machine it can build up on the tension discs and cause the fault you were trying to avoid.
Last reviewed 2026-08-11