Why are my stitches like this?
 

I am using my avatar, a 1958 Kenmore made by Gritzner-Kayser. My top stitches look fairly good. Here's a photo.

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However my bottom stitches are a mess.
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I am sewing fairly lightweight fabric. I am using a size 11 needle. This is a new one, just put in. It replaced a brand new Organ needle, same size. That one kept breaking thread. This one does not break thread. (I am using polyester thread.) I can't figure what to do because it doesn't look like a tension problem, at least not the ones I see pictured on the web. I started with a size 12 needle, I've used 5 needles getting to this one. Same problem with all of them. Could I have a bunch of bad needles? Could it be something else?

Thanks!!

I think the bobbin tension might be too loose??? When have you last had it serviced???

Looks like your bottom tension is too loose. Adjust the screw on the bobbin casing a little at a time until it's right.

I would try a different bobbin, re inserting bobbin and/or cleaning bobbin case and area. It looks like your bobbin thread is way too loose…

Have you worked with the bobbin and upper tensions?

Charlotte

I'll definitely go and check my bobbin tension. I'll do that "yo yo" test. I thought a tension problem would be where there is a straight line of thread either on the top or bottom. That's what my manual and the web says. So tension problems cause these funny stitches too?

I don't get my machine serviced. I don't have a OSMG. I try to take care of it myself. I have the service manual but I'm a rank amateur.

OK. I checked my bottom tension and it was a little loose so I tightened it. But it had no impact on the stitch quality. Then I went ahead and changed my needle yet again. I used another brand new Organ needle. The bottom stitch quality is very much improved but I'm back to breaking threads. What the heck am I doing wrong????

(thanks.....)

Edited to add - maybe size 11 needle is too small and that's why the threads are breaking? Maybe the issues I had with the size 12's were all bad needles? I'm going to try a brand new size 12 and see how that goes. I'm just grasping for straws here. There are so many web sites to diagnose sewing machine issues but I haven't seen this specific problem.

tighten the bobbin tension a little more and use a size 14 for regular weight cotton fabrics and maybe a 16 for heavier weight fabric. I mostly use a size 14 needle.

is it possible that there is a thread caught in the bobbin tension slot?

I'll try a 14 needle momentarily and check my bobbin area again. I do keep it very very clean, I brush it out with every bobbin change. But it can't hurt to look again. Back soon. Thanks!