My rayon threads always shread while embroiedering on tshirts

If the display reads "Check and rethread upper thread", follow the steps below to resolve the issue:
1. Upper thread may be broken.
2. Upper thread may be caught on the spool on top of the machine.
3. Upper thread spool may have run out of thread.
4. Replace the needle in the machine with a new needle.
5. Your needle could be bent or burred causing the thread to break.
6. Check that you are using the correct size thread.
- If embroidering, use 40/50 machine embroidery thread on top and 60 weight in bobbin only.
Turn your machine off and rethread the machine from the start.

There are tests to perform for testing and adjusting bobbin tension. There really aren't any "specifications" other than adjusting it until the bobbin drop test is where it is normally recommended.

adjust bobbin tension Google Search


P.S.--be sure to ALWAYS raise the presser foot when threading the upper thread to insure the thread seats completely in the tension disk.
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The tension(s) may be too tight and could be threaded incorrectly. Start out with a brand new needle. Be sure to RAISE the presser foot when threading the upper thread. Consult the owner's manual to be sure it is threaded in the proper order. Test your stitch on a straight stitch and adjust it so both threads meet in the middle of the fabric. This setting works for straight stitch. However, usually the upper thread tension is loosened a bit for embroidery so the bottom thread will not show on the top of the fabric. Test it on some small embroidery patterns first until it's where you want it.

It is very important to have the bobbin case and the top tension both right. If the thread is getting stuck there is a problem. Always thread the top with the foot up. While threading make small pulls to make sure there isn't any places getting jammed. I've attached a rule document to help you to adjust the tension of the top and bottom.

ALWAYS RAISE the presser foot when threading the top thread. This releases the tension disk so the thread will seat completely.

http://www.husqvarnaviking.com/ko/6953_2494.htm
Not sure if you have looked here but I posted it anyway... Hope it helps.

Call Viking direct

440-808-6550
800-358-0001

thread, threading, hooping all possibilities. Hard to say which without seeing

Each manufacturer have their own bobbins.......not interchangable

Try changing threads. If you're not using embroidery thread specifically, the "treatments" they use on different threads can really cause problems.