Most Common Tension Issues with Vibrating Shuttle Sewing Machines

Hello everyone, I have been piecing a quilt top on one of my Singer vibrating shuttle treadle sewing machines and  I started to run into some tension issues. I remember some erratic tension problems from the last time I used it to quilt a baby quilt. I finished quilting before I found the problem. I decided to track down the cause and share the experience. In hopes that it might help someone else who finds themselves with a gremlin living in their sewing machine.

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Now as the title suggested we are going to be targeting the older style sewing machines with the vibrating shuttle. I say older style because there were still this type of machines in use with electric motors up into the 1960's. Some of what we will discuss can be directly translated or transferred to the more typical round bobbin style cases and tension assemblies.

Left Side - Singer 27 Shuttle  Upper Right - New Home Shuttle Lower Right - National Shuttle

Here is the scenario as it played out, I was using one of my Singer 127 sewing machines, simple straight stitch on typical quilting cotton. Things were going good when my bobbin ran out of thread. Not a big deal I had several other bobbins all set to use, all filled from the same serger cone probably all done at the same sitting, So I pulled the shuttle,dumped the empty bobbin and dropped a full one into the shuttle. It went in fine and threaded through the slot and under the spring. I picked up the bottom thread same as any other machine and started to sew on my project again. Well after about a dozen stitches it started to make noise and half dozen more stitches it was all balled up and locking the needle bar up. I opened the slide plate to see a mess of thread and knots. I cut the project loose. then cut the shuttle loose from the carrier. After checking to make sure all the loose threads were removed and the carrier and feed dogs were functioning correctly I re-threaded the shuttle and dropped it back into the carrier. A few stitches into the project and again the same thing. After clearing the problem again checking the bobbin and making sure it was threaded right, I grabbed some scrap and tried it again. perfect stitches.long row and short rows all perfect. Same fabric as the project. OK, set the project back under the needle and the stitches were still perfect. For about 10 minutes any way then they started to loosen up, the bottom thread was looping on the top of the seam. I checked the shuttle and everything looked OK. Re-thread and start again, instant tangle. Check the top tension,looked good. Bottom tension was loose. I tightened the adjustment to the leaf spring on the shuttle. It helped but the stitch balance was still off. I couldn't tighten the bottom tension further so I decided the top must be too tight and I loosened it. Now the balance was better but the stitch was very loose and sloppy. It wasn't long and the bottom thread was too tight and top too loose and looping on the bottom. I tightened the top tension back to original position. It looked good for a few stitches then back to looping the top again. I thoroughly cleaned the upper tension discs, checked thread path, and this time I changed the bobbin.



Now the shuttle tension spring was so tight that it broke the bottom thread after about 6 stitches. I can clearly see that the bobbin thread was cut off at the leaf spring. I am finally starting to analyze the events and I realize all the problems are revolving around the bobbin and bobbin tension leaf spring. I removed the shuttle and dropped the bobbin out of it. The thread was still caught up under the spring but it wasn't all frazzled and frayed like a cracked spring or worn out spring can do. When I removed the adjustment screw (very tiny) to allow me to remove the leaf spring I began to see what was causing the issue. When I gingerly removed the spring the space between the spring and the shuttle was packed full of 100+ years of old oil,thread, and lint. The old oil had collected the lint and dirt as it hardened into what is best described as varnish. The thread had worn grooves into the surface of the hardened varnish and as a result eliminated the ability to control the bobbin tension. The spring was being held off of the thread by the old varnish.  From the outside it was impossible to see  but once the hardened oil was cleaned off the shuttle and the spring.The spring had to be gently nudged back into its original shape. Suddenly all my bottom tension issues were gone. Once again my sewing machine was happily clicking out perfect stitches. And we buried one more pesky gremlin. If you find yourself having tension issues maybe my experiences will lend you a hand. If this doesn't help but the symptom is very similar I might also suggest looking inside the shuttle with the bobbin removed. I do on occasion find thread and dirty gunk in the shuttle interfering with the bobbins ability to unwind and feed through the shuttle.

Check out Paul's other posts to learn more about caring for your vintage sewing machines.  Also be sure to check out all our vintage sewing machine posts.

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