Quote:
Originally Posted by Robert Young
sorry, to me if the front side looks good... go with it! your bobbin lines are pretty straight otherwise just not centered.
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Actually if you get strait even but offset lines like that more often then not when you go to do smaller details/text you end up having bobbin show on top.
I have run into and solved for this problem before. Usually its a timing issue of being too Early for optimal loop off the needle catching.
The loop that is formed between the needle down position and the hook point position has an optimal catch point where the forces/physics involved creates the least amount of instantaneous tension on the top thread.
Generally its when the loop is fully formed at its largest before the needle starts pulling the thread loop back out/up where the needle no longer manipulating the thread.
That is when you want the hook to make contact with the thread as it hands off the point of tension from the needle to the hook.
If the hook makes contact early you get a weird jolt in the top tension that pulls a small bit of excess thread gets pulled into the material. Because the release time of the rotary hook and the timing of the thread take up happen at the same time as pantograph movement you get directionally biased stitch tensions because the release always happens on the left side of the of a counter clock-ways rotating rotary hook, you end up with a looser top tension going one way because the slack in the thread tension you get a looser side, and a tighter tension going the otherway because instead of the take up lever being what pulls and forms the bottom stitch the pantograph movement is what forms the bottom stitch after the take up lever has fully pulled up the remaining slack... (Thats what I think happens at least I need an ultra high speed camera to confirm the hypothosis)
But in practice changing the rotary hook timing solves the issue (and allows you to lower tensions to reduce puckering issues.)
Whenever I buy up a used machine I always go through lots of testing and adjustments and fine tune the machine far beyond the original from the factory adjustments or even what a technician would adjust for.
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Thread and bobbin tension - offset to 1 side
