Thread is bunching up under fabric - Sewing Machines

Your tension must be wrong. If the top tension is too weak the thread on the bottom is not being pulled through the fabric to form a proper stitch. Try different tensions on scraps of fabric.

Is it really the bobbin thread that is bunching? Generally, thread messes under the fabric are the fault of the top thread, and thread messes on top of the fabric are a bobbin problem.

Top thread bunching under the fabric is called "thread nesting" or "bird nesting" but I prefer to call it thread "barfs." Most often, it occurs because the top thread has not been seated completely in the tension disk.

Install a brand new needle.
Remove the top thread from the machine.
RAISE the presser foot and rethread the top thread.
(Verify the thread path is correct.)
Set the top tension disk at the midway point.

Retest your machine. Tweak the top tension if required.

Check whether it is bobbin thread or the top thread accumulating under the fabric. Generally, if thread problems exist "under" the fabric, it is a top thread issue. If the problems exist "above" the fabric, it is a bobbin issue.

Sounds like a thread nesting (bird nesting) problem where the top thread is globbing under the fabric. Usually, this is caused by misthreading (confirm the thread path), the thread not seated in the tension disk (ALWAYS RAISE the presser foot when threading!), or very loose top thread tension.

Remove the thread. Raise the presser foot and rethread from the beginning. Check that the thread path is correct. Set the upper tension at the midway point between high & low numbers (this is the beginning point for tension and will most likely need to be tweaked for your particular machine).

Sewing Machine Thread Bunching Up Here Why

What causes Bird Nests Superior Threads

Birds nest under the fabric big loops of thread top side looks good...

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adjust the tension to a appropriate setting,
See the video here.
Sewing Help Sewing Machine Problem Thread Bunching Under Fabric
The knob and its location can differ based on the model of your sewing machine.

Sounds like bird nesting. The upper thread accumulates under the fabric creating a series of loops and knots.

First: Install a brand new needle and make sure it is installed facing the correct direction. (A new needle is the least expensive fix for most sewing machine issues.)

Second: Remove the thread. RAISE the presser foot and rethread from the beginning. Make sure it is threaded correctly (consult the owner's manual).

Third: Pull up the bobbin thread through the fabric and gently hold the thread tails in your left hand while slowly taking the first couple of stitches.

How and Why to Bring up the Bobbin Thread

Sewing Machine Thread Bunching Up Here Why

https://answers.yahoo.com/question/index?qid=20100303212248AAnRUQA

Why Do Get Bunched Up Thread Under My Fabric

WHY IS THREAD BUNCHING UNDERNEATH MY FABRIC

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First thing: install a brand new needle.
Second: remove upper thread. RAISE the presser foot and rethread from the beginning. Set upper tension to the midway point between high & low numbers.

These links may be helpful:

Sewing Machine Thread Bunching Up Here Why

5 Common Causes of Birdnests

Why Do Get Bunched Up Thread Under My Fabric

WHY IS THREAD BUNCHING UNDERNEATH MY FABRIC

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Is it really the bobbin thread that is bunching under the fabric, or is it really the top thread that is creating loops and "bird nests" under the fabric???

Rethread your upper thread. BEFORE you thread the upper thread, be sure to RAISE the presser foot. This releases the upper thread tension disks so the thread is firmly seated in the tension disk.

If it continues to be a problem, then the upper tension needs to be tightened. Adjust slightly, then test. Repeat until the upper and lower threads meet in the middle of the fabric.

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check the needle to see if it's bent
check to make sure the needle & thread are right for the project
some sewing machine bunch under fabric when the top thread come off the thread take up lever

tension could be too loose. start with bobbin tension- should allow thread to pass with SLIGHT resistance. then adjust top tension at about 2-3 to start.

Clean the bobbin area and then re-thread the machine with the presser foot up.

Lengthen the stitches.

Test on a scrap of the fabric.