Bottom thread keeps knotting up

SOURCE: I have a Brother SE-270D

its the problem of the timing belt in your machine its extra loosen or extra tightned or is slightly came out of its position or finally broken.
as the machine is proper just missing the proper speed as it should be .
it is running continuosly as you stated.
check the timing belt and make it proper if its worn out and needs replacement this is how its done

There is an adjusting screw on the right side of the machine head. Follow the motor bracket to the machine head and loosen that big old screw or bolt which will raise or lower the motor giving you slack to remove or replace the belt.

feel free for further queries
thanks

SOURCE: thread knotting around bobbin case

hello, I had the exact same problem and could not find the solution until i took my machine to my sewing sensei and i solved my tedious problem. It was actually not a tension problem at all but a threading problem. Make sure you have threaded your bobbin correctly and that when you pull on the bobbin thread that the bobbin turns the right way. (mine must spin anti clockwise to work)  Make sure that when you pull up the bobbin thread using the needle that it is not over the feed dogs connective bar but under it. A big problem when the thread gets caught around the bobbin case wheel is that the thread is looped around the feed dogs once and that causes the thread to get caught around the bobbin wheel. In conclusion, thread the bobbin correctly and read over your instruction book before spending the money to get it fixe in s shop.

SOURCE: needles keep breaking & bobbing wont feed thru

First try taking your bobbin case right out of the machine (not sure if this model has a top loading or front loading bobbin, but your manual will help you here) and floss out the tension slot with a piece of strong thread. Don't use waxed dental floss, but non-waxed would work okay. (The bobbin case is the piece that the bobbin sits in.) Look around while you have the machine open and remove any fluff and thread you can see - TURN MACHINE OFF BEFORE DOING THIS! Replace bobbin case. Replace bobbin and make sure it "clicks" into the tension slot.

Then unthread the top of the machine, clean the tension disks by passing a folded dollar bill (or any paper money, depends on what country you are in) through the disks in the direction you thread the machine. Do this several times. Re-thread making sure you follow the correct thread path.

Make sure the needle plate is on firmly.

If after all that it still won't work, I'm sorry to say that it sounds like you have a misaligned needle bar. This commonly happens after you have a major thread snaffoo and needle breakage. The needle gets caught in the thread knot, pulls to the side and breaks but if it gets seriously caught it can pull the needle bar out of place. You cannot put the needle bar back in place yourself - it's a job for the workshop. Don't sew on your machine until it is fixed. The noise you are hearing is likely to be the needle striking against the needle plate or even the bobbin. Your timing will probably need re-setting too and this needs to be done by a qualified technician.

If you really need to sew before you can get your machine into the workshop, and if you can move the needle position on your machine by pressing a "sideways" button of some sort, you could try to get the needle in the centre yourself using this feature. This will not help if it is the timing that is the major problem.
Pam M.

SOURCE: Sewing Machine (brother XL 3200)

You may have the bobbin case in wrong.  I have this machine, and I know that it is really easy to put the bobbin case in wrong.  Try taking it out and making sure that the little stop is in the front and it is seated down in there and able to wiggle back and forth.  My experience with this machine, until the other day when my cat knocked mine off the table and knocked something out of alignment, is that it just works.  Any time mine hasn't worked, it has either been dirty, needing oil, threaded wrong or the bobbin case wasn't seated right.  In other words, it has always been my fault.

SOURCE: how to stop bobin thread from knotting

When loading the bobbin there is most likely not enough tension on the thread letting it overlap incorrectly. Try wrapping thread around a tensioner when filling and that should help. That way the bobbin is rolled as tight as the tension on the upper thread when sewing.