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?

Date: 2014-04-09 03:58 pm (UTC)
From: [identity profile] onyoukai.livejournal.com
Hey, sorry I missed this - aside from being really busy the past month, I was also having problems with LJ literally giving me a blank page for my friends view, as though no one on my friends list was posting at all. I only just now, in the past couple days, got anything actually showing up, and even then for some reason it's not giving me more than 1 page of friends posts. (Now I'm wondering if there's some new hidden setting I don't know about...)

I'm sure at this point you've already called the shop to get this problem taken care of, but if not, my first thoughts are on the thread and the bobbin case.

Threads that are very large like that nylon can cause problems for automatic threader mechanisms. And with my Ellegante, there are times where the auto-threader seems to set everything up fine, but when I start sewing, I get big ugly loops on the bottom. It usually turns out that the upper thread isn't in all the hooks and tension discs that it's supposed to be in, and when I completely unthread the machine and rethread it again, everything works fine. It's something I don't like about Baby Lock machines: how the upper thread path is completely concealed from view and I have to rely on guesswork AFTER things start screwing up, simply because I can't see when a thread has slipped out of where it's supposed to be. I've taken the chassis off the machine to really pick things out, but it's something I REALLY try to avoid doing because it's a bitch to put back on properly.

Baby Lock machines seem rather finicky when it comes to threads. Apparently they work great with some threads and pitch a fit with others.

I've never worked with a twisted nylon upholstery thread, so I honestly can't share any firsthand experiences with it. However, I have used nylon "invisible thread" in my Viking Rose, and one thing I noticed about it is that it is STRETCHY. If I ran the machine like how I normally sew, it warped like crazy and I had loops in my stitching. To get normal, tight stitching out of it, I had to sew at a very low speed, and I created another "angle" in the upper thread path by physically tugging the thread away with two fingers on my right hand, specifically changing the angle so that the thread had a direct approach to the lever arm and wasn't being pulled and stretched around some tiny corner on the machine body. It's possible that this nylon twist thread is also prone to stretching.

Another possibility is that the bobbin case tension could be at the wrong setting for sewing with this kind of thread. Are you trying to use it in both the top and the bottom? The default bobbin case isn't calibrated to handle thick nylon upholstery thread like this, so I'm thinking that's the issue if changing the upper tension doesn't help. With home machines, generally you use a heavy top thread with a regular lower thread. This was something I didn't know until I took college courses, because this info just wasn't out there to find. I didn't understand why my top-stitching with top-stitching thread looked like shit, but it turned out it was a consequence of putting topstitch thread in my bobbin, too. If you want to have a nylon bobbin thread, you should probably get a second bobbin case that's calibrated for that kind of thread. For that, I'd call the shop you bought the machine from and ask if they can calibrate a bobbin case for you.

Date: 2014-04-12 04:13 am (UTC)
From: [identity profile] amethyst73.livejournal.com
Huh! I hadn't thought of the _upper_ threading being off. I would bet you're right that the thread slipped out of something up top, because it had been behaving fine.. up until the point when it didn't (upon switching from triple-stitch to overcasting was when it started misbehaving). I actually haven't called the shop yet; I was able to complete the project with less insanely thick thread. (Truth be told, the heavy cotton thread is going to be fine going forward, and it gives a much less stiff final result than the nylon did. Triple-stitching PLUS overcasting with nylon gives you rather stiff edges!)

I was using the nylon in both the top and the bottom, because I didn't have any idea that you weren't supposed to. (Like you said, it just isn't mentioned anywhere.) I'm not making any more bags in the near future, and I'll bring along the sample that I photo'd here to the next embroidery club that I get myself to, and ask about it then.

Thanks, as always, for your help and diagnosis!

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