amethyst73: (tazz)
[personal profile] amethyst73
So, I was putting together the bird bag earlier today.  I use a light cotton duck for the body and a (undoubtedly unnecessarily heavy) nylon thread for sewing, with an (also undoubtedly unnecessarily heavy) 110/18 jeans needle.  I start with a very long piece of fabric, fold it in half (with the fold being the bottom), sew up the edges with a triple seam stitch, finish the seams with an overlocking stitch, and then use standard straight stitching for the top and attaching the handles.  The stitch length is generally 3-3.5 mm to account somewhat for the heaviness of the fabric; I may be Doing It Wrong and having the stitches be kind of too big, but the standard 2.5 mm made things behave badly.

With the exception of the tension looking skewed with a bias strongly towards the bobbin, the thread has always behaved reasonably in the past. (I try to make up for the bobbin by adjusting the tension to somewhere between 4.4 and 6, which sometimes helps a little.)  Not so today.  I was able to do the initial triple-seaming down the sides without particular issue.  But when I started the overlocking, something just wasn't working right on the bobbin side of things.  It seemed really loose and wasn't holding together properly.  After running a quick test, I ended up overlocking with standard Aurifil cotton, which behaved fine.

Then I took a look at what happened with a plain old straight stitch.  It looked fine on the top:



but the bottom was completely messed up:



Running a similar test with the Aurifil cotton thread behaved rather better (front not photographed):


(Aurifil on left, nylon on right)

A heavy-duty cotton Coats and Clark thread also behaved well on the back, though it (and the Aurifil) both had the same sort of issues with bobbin tension beating out the upper thread tension, which I wasn't ever able to entirely resolve.  I was however able to complete the bag with the heavy-duty cotton.

What's going on with that nylon thread?  I'm guessing it's missing the two little notches in the bobbin case when it's auto-threaded.  (FWIW, it also has decided it's not going to clip with the machine thread cutter.)  Any hints on what's going on?  Can I fix this on my own?
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