Just a little tip (I have never seen this one anywhere). Once in awhile, you will be stitching along when the bobbin thread comes to the surface. You may have been stitching for a long time before it happens. You know that occasionally the bobbin does not get 'in tension' at the beginning of your project, but this is much later in the design.
This peek-a-boo has happened to me a few times. It can happen when you are using cardboard bobbin spools. It is caused by your
bobbin spool becoming too light weight allowing that spool to jump and get out of its tension path. You can see that this spool is not yet going to be alerting you via the bobbin thread sensor. But so much of the thread is gone that the piece weighs nearly nothing.
By the way, when I did use cardboard (I switched to plastic some time ago) spools, here is another tip - I bought a 'box' which was a gross or perhaps 100 spools. An instruction page was inside the box saying to 'REMOVE' the top cardboard of the spool so that the thread sensor would work correctly. I know many of us buy bobbin spools in packs of 10 or similar quantities, therefore instructions may not be present. I don't know if all the cardboard bobbin manufacturers would say that, but mine did.
At less than 35 cents per spool AND consistent, evenly wound thread,
these bobbins are a bargain. They sew a great deal further than a 'home wound' bobbin.
Lastly, on the subject of bobbins, if you missed out on my tip for inexpensive
bobbin thread holders, check my blog.
I do like to let the newbies who may be reading me for the first time, or the 51st time, some of my blogs have been really notable. IMHO, the Bobbin Thread Holder is one of them.