Sewing machine issue
 

I am piecing together some blocks and I just notice the bottom tread is all tangled up on the piece I just sewn.
Can someone help me figure out why this is happening

A problem on the underside usually indicates a problem with the upper thread path. Rethread the top of the machine making sure there aren't any tiny pieces of lint or thread anywhere. Also make sure your pressure foot is up when you thread it so the thread gets seated in the tension disks completely.

Change the needle.

Check the bobbin. Make sure the thread is wound firmly.

Check the bobbin area for any stray threads.

My machines are older- I usually pull both threads to the back/ behind the needle and hold on to them when I start a new seam.
Doing so seems to help prevent that mess on the back.

Ye, this is usually the problem, please follow this advice.

Both my modern and vintage machines will do this at the beginning of a seam. I usually have a leader piece about 2 inches long that I sew on before I begin sewing on the real thing. If I don't have one available, I start sewing about a 1/2" down the seam instead of at the edge, go backwards a few stitches and then go forward to lock it. I always start needle down. I also think taking smaller stiches helps to abate this problem.

Good luck! You'll find what works for you!

Every once in a while, my upper thread will twist and loop, and that gets pulled through the tension disk. This causes a few inches of extra thread that gets pulled to the back side and nested up, but is often too small to cause a thread break so it all looks fine on the top side, and is only in one spot and then it's fine again.

however sometimes this causes the thread to pop out of the tension disk, but then I usually end up with a thread break and know it a lot sooner.

I've found some thread is more of a problem, and have needed to adjust the thread path to keep it from happening. With my embroidery machine, I'll put the thread nets on and that really helps for the more bouncy thread.