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I hope some older specialists in sewing machines might see this and give me some guidance. Or perhaps somebody else got a clue. Lately I noticed a blogger writing about sewing knit stretch delicate fabrics with low tension. She got the impression, that the older type long shuttle machines is able to sew with lower bobbin thread tension than newer machines, as we know them. This is the blog: https://vintagesewingmachinesblog.wordpress.com/2018/04/20/that-elusive-flexible-stitch/ So I have tried to do some experiments with a household vibrating shuttle machine, and this is a photo of it: It is a quite heavy machine with some interesting mechanical details. I did however put on a motor and something to gear is somewhat down to make some experiments. In one trial I sewed Tex 210 thread in vinyl. However I got some issues regarding stitch balance, and I am not quite sure how you should expect to set timing of the shuttle movement in relation to the take up lever. The timing you know from normal sewing machines between needle and hook is not that much an issue with long shuttle machines, because you got a special movement of the needle bar with two dips for each cycle. This kind of needle bar movement is also used with patchers like the Singer 29. Therefore the needle do not move much when the point of the long shuttle catch the thread loop. Furthermore this kind of machines do not have any hard point in sewing cycle as normal modern machines, because the needle remains down while the needle thread is pulled down. So in this special way this kind of sewing machines got an advantage with heavy fabrics compared to normal leather sewing machines. I think this kind of machine cause less wear on thread too. When I got the machine, the timing was like this: 1) when the long shuttle is in most forward position, the full bobbin thread tension is applied to fabric. At this position, the take-up lever is 6 mm (1/4 inch) lower than max height. 2) When the take-up lever is at max height and the upper thread tensions is applied, then the shuttle have moved 5 mm (1/5 inch) back from max forward position, so it somewhat have loosen the lower thread tension. I have tried to move the the timing a bit so the shuttle only moved 2 mm back at max take-up position, but I am not sure I can identify any sewing quality change. I have tried to look in a German book for sewing machine mechanics from about 1955, but it do not provide clues on this. So I hope that somebody in this forum may have got some knowledge about this timing.