In this video, we show how to check whether the bobbin tension is set properly on a Toyota ESP 9100 using the H test. To do this, we sew a block-style font sample and then turn it over to inspect the back of the stitching.
When we examine the back, very little to no bobbin thread in the middle of the columns usually means the bobbin tension is too tight. If we see all or most bobbin thread and very little top thread, the bobbin tension is most likely too loose. Ideally, we should see a balanced result: one-third top thread, one-third bobbin thread, and one-third top thread.
If the stitching appears too tight, the bobbin tension may be too tight or the top tension may be too loose, and the opposite is true when too much bobbin thread is showing. To correct this, we adjust the main tension knobs slightly, loosening or tightening by about a half turn, three-quarters of a turn, or at most one full turn. It does not take much adjustment to compensate for the issue.
Looking to fine-tune your machine's tension? Check out our tension tools and supplies.