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Bobbin Spring Tension on Treadles, Handcranks, and Electric Sewing Machines

Hello everyone, today our topic is bobbin spring tension on vintage sewing machines. It doesn't matter if the machines are treadle  sewing machines or electric machines, or if they have round bobbins in them or shuttle type bobbins, with two exceptions I can think of off hand. The first exception would be a third type bobbin assembly which I am unfamiliar with, transverse shuttles were used on some very early and antique sewing machines and I haven't experienced any of these at this time so I won't repeat what I have only read about. The second would be the (White) designed rotary bobbin which we will address later in the post.

necchi bobbin and case

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In an earlier post, I discussed some of the overlooked things about tension issues and discussed the cause and effects of a good cleaning. Now I would like to call attention to the simple mechanics involved and offer some insight to the inexperienced sewers who have been led to believe the treadle machines and vintage machines were made to compete with commercial machines. No, they were not. Yes, they do handle some thicker seams and heavier material easier than the fantastic plastics. Only because history shows the fabric available then to be heavier than most of the fabric now. It does not suggest we load a bobbin with bailing twine and sew canvas tarps together.

The bobbin or lower tension, as it is sometimes referred to, is adjusted by tightening a screw against a flat spring and the spring, in turn, pinches the thread leaving the bobbin creating the tension needed to manage the loops and balance the stitch. It is the same principle for shuttles as it is for round bobbin machines. Most machines are designed to accommodate a wide variety of needle eye and shank  sizes and will usually have a chart to show what needle to match the desired thread size. These work very well and cause minimal damage. The problem starts when we as individuals decide to use heavier thread than what the spec sheet shows the machine was designed to use. When this occurs generally it works for a while and gets us through the projects in fine order. No, harm no foul until we realize we can no longer control the stitch balance and quality when we switch thread sizes. The thinner the thread the more problems we have with loops on the top and the screw is already bottomed out with no more adjustment left. The heavy thread has either worn a groove into our spring due to friction or it has bent or cracked our tension spring.

Now our choices are to replace the tension spring or the entire bobbin case or try to polish the groove out and gingerly bend the spring back to a usable shape. First I would recommend don't go above design, if you do,check into replacement parts availability and use a machine you can get parts for. I would recommend  a second bobbin case when possible just for a heavier thread within the designed parameter. It is much easier to swap out bobbin cases than it is to readjust the tension every time if you change thread sizes often.
singer shuttle bobbin

The White sewing machine company designed rotary bobbin case. These machines were built and or designed for several different labels such as Free,Westinghouse, and Kenmore. They are different because they do not use the flat spring pressure technique. Instead, they use a compression coil spring with a screw adjustment in the center to compress two surfaces together and pinch the bobbin thread applying the tension as needed. They seem to be as suited to the task as the flat spring counterpart. But they are not as easily found and not recommended for heavy work for that reason alone. We have a few around here and I have never found them a problem to use or adjust.

white westinghouse bobbin

All in a nutshell, yes they can sew heavily, they were not designed to replace commercial machines and should not be used continually on overweight materials. They will do a wonderful job until they break. After all, how do you find out just how much it will handle? Push it till it breaks. I hope this reminds the experienced as well as gives the inexperienced food for thought good luck with your machines,may they bring you as many hours of enjoyment as ours does for us.

Want more vintage sewing machine posts?  Be sure to check out all of our treadle posts and electric sewing machine posts.

bobbin spring tension issues

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