Symptoms
- Tangled loops of thread on the fabric's underside
- Fabric puckers or jams under the needle plate
- Machine may stall or the needle can break
- Top stitching looks fine while the bottom is a mess
Likely causes
- CommonIncorrect or incomplete threading of the top threadIf the thread isn't seated in the tension disks properly (often from threading with the presser foot down), tension goes uneven.
- CommonBobbin inserted incorrectly or wound unevenlyA bobbin put in backwards or wound with uneven tension causes the underside to loop.
- PossibleLint buildup in the bobbin case or tension assemblyTrapped lint changes how thread feeds through, disrupting tension.
- PossibleWrong needle size or type for the fabric/threadA mismatched needle can cause poor thread interaction at the stitch formation point.
What to do
- Raise the presser foot before rethreading the top thread, since tension disks only engage properly when it's up.
- Rethread the top thread completely, following the machine's threading path exactly as shown in the manual.
- Remove the bobbin and check it's inserted in the correct direction, with thread unwinding the way the case shows.
- Rewind a fresh bobbin evenly at a moderate speed if the current one looks sloppy or uneven.
- Clean out lint from the bobbin case and feed dog area with a small brush.
- Check the needle for the correct size and type for your fabric, and replace it if bent or dull.
- Test on a scrap of fabric before continuing your project.
Tools and parts
- Small lint brush
- Fresh bobbin
- Replacement needle
Universal sewing machine needlesSearch: “sewing machine needles assorted sizes”
When to call a pro
Take it to a sewing machine technician if rethreading and cleaning don't fix it, since it may point to a tension assembly or timing issue.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.