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I recently bought a Pfaff 360. I've used sewing machines before, but this is the first I've actually owned and I don't recall this being an issue I've noticed. I believe I have the tension settings correct (based on the "dangling bobbin" test, and adjusting the upper dial), but it looks like straight stitches are slightly slanted.

Straight stitch showing slanted thread

The needle entry points look OK, so I don't think this is an issue with one of the zig-zag cams being engaged by mistake. For example here I've just run some fabric through to puncture it:

needle entry pattern

my accuracy in sewing a straight line/fabric stretch aside this looks like random jitter to me.

I've also read that this can be caused by torsion in the thread, which is just some Gütermann polyester. But I wondered if I have some remaining tension issues. I wouldn't say the stitches are obviously loose and with different top thread/bobbin colours they're well separated.

Here's a GIF - it does look like the needle is coming down slightly at an angle, but it's hard to really tell if this is an optical illusion or not (I'll get a video with less shaky cam).

enter image description here

Side view:

enter image description here

Josh
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  • I saw something similar on my bernina the other day. Turned out I'd accidentally increased the stitch width while it was set to a straight stitch. But I'm not sure that's what you're seeing (hence not an answer). – Chris H Aug 10 '23 at 10:33
  • The Pfaff has a dial for width adjustment (zig-zag) and I wondered if it was slightly miscalibrated, but I'm not sure that's the issue. Maybe I can try and set up a video and manually advance the needle to see if it's moving from side to side? – Josh Aug 10 '23 at 10:38
  • I managed to see the needle moving on close inspection, so that's possible. Video is good because it would allow you to compare the motion with the machine threaded and not. – Chris H Aug 10 '23 at 10:49
  • Another thought - if you unpick the stitches, what does that line of holes look like – Chris H Aug 10 '23 at 10:50
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    I just uploaded a GIF - bit wobbly at short notice but gives an idea. I'll get something set up with a tripod later, this is just handheld with a camera I have lying around. Should be able to get something where we can see the thread getting looped too. From a first glance it looks like the needle is puncturing the same spot every time, but the motion isn't perfectly vertical? – Josh Aug 10 '23 at 11:02
  • Maybe it's just a weird effect of watching the slow-motion gif, but is your needle straight/not bent? Have you tried replacing the needle? – Allison C Aug 10 '23 at 15:14
  • Hi @AllisonC yeah I wondered about this. I tried with a spare that I have on hand, but I might get some more from the store and try those. However same result with the spare (the needle doesn't look obviously bent either). – Josh Aug 10 '23 at 22:11
  • @Josh thanks for the info! I'd suggest some new needles; they should be replaced regularly anyway, and even if they aren't bent it's possible they've become dull and that's having an effect. Good luck! – Allison C Aug 10 '23 at 22:28

2 Answers2

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From what I can tell, this is completely normal. At least, if it's not normal, my machine does the same and I've never had any issues with it. If it makes you feel better, the same phenomenon happens to other people, too:

enter image description here

The actual stitch holes are all in one perfect line. Between the stitch holes run 2 threads, one above and one below the fabric. Exactly in the stitch holes both threads cross each other twice to form the actual stitch. (Sewing machines do that in the bobbin compartment by grabbing the upper thread and moving a loop of it once around the bobbin.)

This crossing cannot possibly be straight for both threads, they physically have to wind around each other. So one thread must move to the left while the other moves to the right. That's why the threads look slanted while the holes are in a perfect line.

I hope this schematic of a machine stitch by Coles Sewing Centre makes it clear:

enter image description here

When the tension is set correctly, the threads should cross right in the middle between both layers of fabric. Since the threads have to wind around each other, one must lean to the right and the other to the left, it's impossible for both threads to be perfectly straight. If you could remove the fabric, you should see both threads forming a double helix.

If the tension is too low or too high, one thread is straight(er) and pulls the crossing loop of the other thread to the top or bottom of the fabric. The low tension thread has more room to move and twist around so the high tension thread is kept relatively straight.

Elmy
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  • Thanks! Yes, I've noticed that the slanting actually occurs when the needle is on its upwards path and the thread is drawn over to one side as the loop is formed, I guess for the reason you've mentioned. What I've noticed is that this isn't as apparent if I use a much thicker fabric - for example nylon webbing. The Pfaff also has a horizontal spool holder which is supposed to work better with cross-wound threads and I wondered if that might help (because coming off the vertical spool, the thread looks pretty wavy, though I think the tensioner should compensate for that). – Josh Aug 29 '23 at 13:06
  • (Pfaff also have quite a nice diagram in their manual which looks very similar - the instructions for adjusting tension are a lot more comprehensive than I expected when I bought it) – Josh Aug 29 '23 at 13:08
  • @Josh Honestly, I wouldn't worry abount it. I don't think that the bobbin style has anything to do with it because the balanced tension of both threads shound negate any curling of the thread caused by any bobbin. If it bothers you, I noticed that the effect lessens with a shorter stitch length and that the bobbin thread looks straighter than the upper thread. So for example when you hem a garment by turning the edge under twice and sewing over it the neat line is outside and the slanted line hidden inside the garment. – Elmy Aug 29 '23 at 19:42
  • I've marked this as the correct answer because after playing with some other fabrics, it seems to be a lot more prevalent with thin/stretchy stuff. If I go through something heavy (like velcro) it does seem to be straight. – Josh Sep 16 '23 at 21:39
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Have you tried changing the needle. Sometimes even a slight bend in the needle could do this. Always try the more simple fixes before moving towards paying out of pocket to get it fixed.

Priscilla Botirca
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  • Thanks! I did swap out the needle with no difference - I will also check some new thread today, I wonder if it's some weird torsion going on. But I also wanted to video the needle being threaded too (but this is more of an excuse to play with the camera) – Josh Aug 17 '23 at 10:46