I cannot figure out why the bobbin thread cannot be picked up when I lower the needle.
Take a look at the following video about how a sewing machine works...it's super short and it'll help with the explanation.
From the video you saw that the needle comes down and the rotary hook grabs the thread pulling it around to catch the bobbin thread.
If something prevents the needle thread from coming around it can't grab the bobbin thread and bring it up.
Problems you can fix...
Check to see that your needle is fully inserted into the needle clamp. If the needle is sitting too low, it doesn't allow the thread to loop at the proper time and the rotary hook can't catch it to do it's job.
Loosen your needle tension just a tad. You'll still want a balanced stitch, but usually you can reduce the tension a bit and still have a good looking stitch.
If you're sewing through higher thread count fabrics, like batiks, switch to a Microtex Sharp needle. This needle does a better job piercing the high thread count material.
If your fabric is 'flagging' (i.e. pulling up with the needle) that would also inhibit the formation of the loop and prevent the bobbin thread from being grabbed. The Microtex Sharp would help there also.
Make sure that your needle thread is properly seated on/in the uptake lever. That would prevent the loop from forming.
And so with any problem, change to a new needle. A damaged needle can also keep the thread from being at the proper place to form that loop.
You need a dealer's help...
...if none of these work.
It may very well be that the timing of your sewing machine is off. This could have happened by sewing over pins or hitting a pin with your needle. It does mean a trip to your dealer for an adjustment.
Sewing machine problems are so FRUSTRATING! But I hope that one of these suggestions works for you.
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