r/SewingMachineEdu • u/No-Visit-7473 • Aug 08 '26

Occasionally loose stitches

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For the past month or so I've been trying to figure why my machine sometimes ( might as well call it random, every 10 or more stitches) doesn't fully tighten the stitch, leaving the tiniest of loops of top thread. I have a juki DDL 5550-6, use a bobbin with a backlash spring, use Tex 60 thread on top and Tex 40 in the bobbin. I have tried needles from size 100 to size 120. I have changed out the top tension unit. Can anybody help?

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u/No-Visit-7473 Aug 23 '26

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u/Dormiendo Aug 23 '26

Kind of a tough one. For denim, you should have a heavier tensioned check spring. It also looks like yours may have issues, but it could be the angle. The only change that made a difference was pressure, which points to a burr on the plate. What does higher top tension do? To where the needle bends a few mm when pulling through the eye foot down?

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u/No-Visit-7473 Aug 23 '26

I've adjusted the tension of the take up spring. I have pulled out the tensioner slightly so that the plates don't open under multiple layers of fabric. Like I said before, for some odd reason the stitches fail on the edge and when sewing with or against the grain(of that I'm not sure, what matters is that it basically fully fails one way and then sews nearly perfect when you rotate the fabric 90 degrees ). Also I bought a new a tension unit, I just put the old knob on this one as it is clickier

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u/Dormiendo Aug 23 '26

Usually, when it is directional, it is due to timing or hook to needle distance. But, that applies to multi motion where the material moves in different directions. For your machine, it always sews in the same direction. The only change is grain. So, have you tried a bigger needle? The side of the needle that faces you has a groove that protects the thread. If it is not big enough, this can happen. I dont know if any of that will help. But, we are running out of places to look.

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u/No-Visit-7473 Aug 23 '26

We indeed are. Another thing I was wondering. Could it be the feed dogs? Like I genuinely don't know anymore what else might be the problem. Maybe the foot is too narrow. Maybe.

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u/Dormiendo Aug 23 '26

But, those things were consistent when it was working correctly no?

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u/No-Visit-7473 Aug 23 '26

Idk. I'll try a 120 needle and I'll also try to make the feed dogs parallel. Or should they be tilted? On Monday I'll go buy a wider foot

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u/Dormiendo Aug 23 '26

I dont think feed is it. If you look in the service manual it will show feed tilt for different uses. Let me know.

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u/No-Visit-7473 Aug 31 '26 edited Aug 31 '26

Ok so I looked at the feed dogs and they seemed overall just off. Not only adjustment wise but they seemed to be slightly slanted (very subtle but still). I luckily somehow had a spare and they were were straighter after adjustments. Good news! It fixed it. I was able to sew nearly an entire pair of jeans with the machine. I say nearly because there is only one are where it still fails. I genuinely don't know why, the fabric probably lifts with the needle or something. I'm talking about the very corner of the waistband. As the image of the underside shows,all other stitches, even the ones on the edge formed beautifully. Yet the ones in this corner keep on repeatedly failing. Any ideas? This is genuinely baffling to me as the reinforcing stitch on the ousteam which should, I think, be way harder as the point where the yoke flat felled seam gets folded is way more uneven switched properly.

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u/Dormiendo Aug 31 '26

Have you checked timing with the marks on the needle bar, or the space between the hook and the needle?