The timing of the needle/hook may be off which happens often if the needle strikes a pin or something else it shouldn't. If a brand new needle has been installed facing the correct direction and it is still hitting under the needleplate, then the timing needs to be addressed. There are many web sites and videos online explaining sewing machine timing that you can try if so inclined. Otherwise, take it for service.
Is it the right size needle, some needles are longer than others. Is your bobbin case in correctly, is a needle pushed all the way up before you tighten their thumb screw if it wasn't tightened it may have come loose and drop down just a bit
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The timing of the needle/hook may be off which happens often if the needle strikes a pin or something else it shouldn't. If a brand new needle has been installed facing the correct direction and it is still hitting under the needleplate, then the timing needs to be addressed. There are many web sites and videos online explaining sewing machine timing that you can try if so inclined. Otherwise, take it for service.
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Is it the right size needle, some needles are longer than others. Is your bobbin case in correctly, is a needle pushed all the way up before you tighten their thumb screw if it wasn't tightened it may have come loose and drop down just a bit