If you have a Singer vibrating shuttle machine such as the model 27/127 or 28/128, this is some preventative maintenance that you probably need. Because the steps are the same, this applies to all vibrating shuttle machine for any manufacture. It’s really easy to do and it will assure that the bobbin tension is smooth and consistent.
This is a shuttle from an antique Singer model 28. From the outside, it looks pretty good.
The small screw at the nose of the shuttle adjusts the bobbin thread tension and attaches the flat spring to the body of the shuttle. Simply remove this screw and detach the flat spring from the body of the shuttle.
Very often, you will find some crud under the spring and inside of the shuttle. Maybe not this much, but remember, anything that obstructs the smooth passage of the bobbin thread will cause tension problems.
Remove all of the debris and if you can, polish the shuttle. Just be sure the surface is as smooth as it can be. Once clean, reassemble it, insert a bobbin and pull the thread up under the flat spring. Adjust the tension screw until the thread has a slight resistance pulling it from the bobbin. This will get you in the ballpark tension wise, and for a good balanced stitch, the final tension adjustment can easily be made while in the machine.
You will find the bobbin tension is more consistent and it is much easier to adjust for a balanced stitch.
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