Cotton is not threading up from bobbin. - Janome 6019QC Mechanical Sewing Machine

it is called bird nesting and the upper thread tension is not tight enough
Proper needle thread tension is when you feel resistance as you pull the thread through the needle eye

Yes it usually is caused by lack of bobbin tension. The bobbin tension doesn't usually change by itself though, so check for other reasons before changing it. Can you feel some tension when you pull the bobbin thread?
Is the bobbin cotton threaded correctly through the bottom tensioner? Is it the same size as the top cotton?
Is the top cotton correctly threaded and freely moving through its path? How much tension is felt when you pull it?
Good luck finding the problem.

Might be a silly question but is your machine threaded correctly? Are you using a new needle, and new thread suitable for the material you are using? Also correct tension with the same thread in bobbin and top thread? :-)

Be sure to use a brand new needle. A bent/damaged needle may have difficulty picking up the bobbin thread.

Verify that both upper and bobbin threads are threaded correctly. If so, and it still fails to pick up the bobbin thread, most likely there is needle/hook timing issue. Take it for service.

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Is the spool thread catching on something (like the little notch on the thread spool) or is wrapped around a thread guide? That will tend to break the thread.

Check that you are using the correct kind of needle to match the thread and fabric you are sewing. (Are you using good quality needles? Might try a different brand.)

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0ahUKEwjJ7Nm4u-bMAhVl6YMKHdOqBwIQFggjMAE&url=http%3A%2F%2Fwww.schmetzneedles.com%2Flearning%2Fpdf%2Fschmetz-needle-chart.pdf&usg=AFQjCNHTR52AmqwzvyCjbXmD5Ch52Va5_Q&cad=rja

All About Needles

Something else to consider is whether the thread is old or bargain bin variety. Try a different brand (preferably a better quality brand) of cotton thread. Threads have really improved over the past few years. If the thread is shredding at the needle eye or you see little fuzzies on the thread (similar to the old cotton-wrapped polyester threads of the 70's), it is not good quality and should be thrown away or used somewhere else.

Another thing to check is whether there is a rough spot on the needle plate or in the bobbin area that may be snagging the thread. Wrap your index finger in some very fine fabric (old pair of hosiery, chiffon, etc.) and rub your finger around and see if it snags anywhere.

Verify that the bobbin is loaded properly in the bobbin case.

The tension could be too tight. Remove the upper thread from the machine. RAISE the presser foot and rethread from the beginning--confirm it is threaded correctly. Set the tension to the midway point between high & low numbers. Retest. The tension is correct when the upper and bobbin threads meet in the middle of the fabric.

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Check to be sure the needle is installed correctly. If the flat side is facing the wrong way, your machine will not stitch.

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Most likely a timing issue. the needle hook and needle are not aligned correctly.

have you tried a youtube video that shows the bobbin winding for machines like your?

Paul... youtube it.... It's really not difficult. Have to load bobbin with thread first... install bobbin (under the needle plate in its holder) thread cotton from top of machine through the correct catch points to the needle.... catch the thread from the bobbin..... pull threads under pressure foot (but look in youtube... loads of vids)

Lint and or thread has collected behind or under the bobbin. use a q-tip (cotton) and swipe out and around the bobbin and bobbin case. Use a can of air and blow out and around the bobbin area. Remove the spool thread from the machine and rethread the spool and bobbin thread in machine.