Ok.
I have checked - no damage to the hook. The broken needle did hit the feeding foot. I have sewn for one hour now in thinner materials and the machine works fine with this stack of materials:
from top: 4mm leather + 18oz waxed canvas + 1,5mm rubber.
perfect result.
If I move up one layer of canvas the splitting starts. This stack is though in a different order:
from top: 18oz canvas + 1,5mm rubber + 18oz canvas + 4mm leather.
It seems that the thread loop that the hook shall cach is to tight - resulting in missing one or two fibres.
I have worked for a few months on a singer 29k and when the materials get thicker it offers a way to adjust the take up.
Is there a way to feed more material to the thread loop on a Dürkopp? or shall I try a bigger needle and less tention?
Using a 120 needle and a serafil 15 thread.
Thanks