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Montag, 14. Januar 2013

Seam quality depends on shape and length of counter tip of the sewing hook

If the seam quality is poor even though stitch regulator, hook and thread tension are well adjusted, the reason can be the following:
The counter tip of the hook together with the thread tension spring should control the upper thread as long as possible without drawing and feeding it from the thread reel for stitch lengths up to 4mm. For stitch lengths above 4mm, there should only be enough thread feed by the hook counter tip that the thread can be tightened well by the thread lever. Only an optimal shape and length of the counter tip of the hook can ensure this.

The counter tip should have its smallest width at "a". A cutoff at "b" is not allowed.

The distance between hook tip and hook counter tip should be 0,2 mm with a tolerance of +/- 0,4mm.
Hook counter tip: Pic. 1: Regular measure, Pic. 2: maximum difference, Pic. 3: lowest difference (overlapping)

If the hook counter tip is too short and the shape of the tip is too slim, the upper thread will fall down too early and will twist. This may lead to knots on the lower side of the fabric. If the hook counter tip is too long and cutoff at "b", the upper thread will fall down too early and will be feeded without tightening. This will lead to loops on the lower side of the fabric that are not tightened. When using unelastic threads (e.g. cotton), the thread may break.

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