JoeJr

I recently came back to this, having reviewed the links from Janey, and letting it roll around in my head for a while. I rechecked the needle bar height, for starters, and tweaked it a little a bit. While I was at it, being a person who likes things straight and being the smartest (and only) person in the room, I eliminated the annoying slight cant in the needle bar. Turns out, further along in the service manual, that annoying slight cant in the needle bar is supposed to be there...so much for being the smartest guy in the room. I checked the timing after adjusting the needle bar height, it was off-a little behind, actually off before I adjusted the needle bar. Not sure if I did it incorrectly the first time. So I corrected that. I ran a bunch of stitches as in the pictures. The top stitch always looked fine, the bottom not so much. In one of Janey's links the person had the timing advanced slightly, so I tried that, not much change. Someone else had suggested bobbin thread tension, so I was adjusting that also, only an 1/8 of a turn at a time, which made a lot of difference surprisingly. I finally settled on leaving it as is and if I ever zig zag with it, it won't be much.

I did learn one thing, something true VSM veterans have probably been doing all along. I loaded up test bobbins (class 15s and 66s) with bright green thread, bright orange for top thread, I bought needles with known sizes for different test fabrics, instead of relying on eyeballing needle sizes from the catch all container. Unfortunately the people at the fabric store didn't really understand what I was trying to do, set up a test packet including different thread sizes for different needles, so I ended up with all purpose thread (I couldn't discern much about thread sizes from the 12,000 spools I was looking at).

But now I'm ready for the next machine.

1.41

The thread might not be coming off the spool evenly. It might help to increase the top tension to deal with this. It might also be that the thread isn't suitable for sewing machines or for your particular machine.

You can do a quick test by holding say 3 or 4 feet of thread between your hands. Slowly bring your hands together. If the thread twists onto itself it's not suitable for sewing machines. If the thread droops down straight it's fine.

I should add that it may also be that your needles need to be thrown away. If they've been used for a few hours they may simply be too dull. They may also be badly made. The edges of the eyes of inexpensive or "no-name" needles are generally not polished to the same quality level as brand name quality needles and thread simply does not move through the eye at a consistent tension.

Finally, I'm a bit confused by your picture. I believe you are showing both 15 class bobbins and 66 class bobbins. You're not by any chance not using the correct bobbin in the machine?

JoeJr

Although I have been known to use the wrong bobbin (see my last post over here World's Best Sewing Machine ) in this case I was using 66 bobbins. I tried the top tension at everything 8 and under on the dial. The last picture is my "test kit" for use on machines after I clean them up. The needles are brand new, but I can switch anyway. I will try testing as you suggest, and I think I will also switch to vintage 66 bobbins, can't hurt.

quiltedsunshine

What you're trying to accomplish is what I would call a "balanced zig-zag." I've learned that not all machines can accomplish this feat. What we did at the shop is get the tensions balanced, so the top and bobbin threads aren't poking through on either side. Then we evenly adjust the top and bobbin tensions tighter. Thread quality does matter. At the shop, we could never get a balanced zig-zag with Coats & Clark sew all thread. When you pull it through your fingers, it has a vibration that you can feel. Try a Guterman or Metler, 100% cotton or 100% polyester thread. It really does make a difference!

JoeJr

Yes, a balanced ZZ is what I'm after. I will hit the store again for different thread.

And thanks to everyone for all the suggestions and ideas!