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I noticed that the patcher sewing machines got a special movement of the needle bar compared to most other sewing machines. This is a video of the Chinese patcher sewing in some transparent fabric. Make note of the screw that fasten the needle in top of the picture: https://youtu.be/LOliY3NHg_A The needle height is controlled by a cam in the flywheel of the machine, and the hook position is controlled by another cam in the flywheel. The needle penetrates the fabric and goes to minimum height and a bit up again to form the loop of the upper thread for the hook to catch. Then the needle is hold down at same position a long time, while the hook moves forward and pulls down the thread. Then after this hook movement have finished the needle is lifted up. For normal sewing machines, the needle position is controlled by an eccentric on the main shaft and a connecting rod to the needle bar. Then the needle eye is lifted through the fabric and further up, while the hook pulls down the upper thread. This way causes a peak in thread tension near the hook, because the friction on the needle thread is high when the needle eye passes the fabric. This video explains this problem from 0:50 to 2:20 in the video: https://youtu.be/80WASgbKIX4 It is not only the Chinese Patcher, that moves the needle this way. The Singer 29, Adler 30-1 and some older sewing machines like the Singer 28 got a similar movement of the needle. I am sure, that in this way it is easier for the hook to pull down the thread, because the friction to the thread in the grove of the needle is limited. And therefore I guess that it may be possible to sew with smaller needles than normal with these patchers. Goto 10:50 in this video to see a similar movement for a Singer 29-4: https://youtu.be/aQLre-l5RkU Perhaps more leather sewing machines are made with this special needle bar movement, but I have not noticed that. Have you? I guess that you got some other disadvantages with this kind of cam controlled needle movement, and therefore most other machines are not made this way. I think one problem can be vibration at higher sewing speeds.