Problem with hook gib (Gegenspitze) on a rotary hook Dürkopp 291

[Gymnast]

I know the German term, "Gegenspitze" for a point part of the hook, where the upper thread leaves the area, when pulled the last part up by the take-up lever. It is the point you see here:

For some machines like the Singer 211W this "Gegenspitze" is part of the hook gib.

My problem is, that the thread is pulled hard by the take-up lever on this Gegenspitze before the thread finally is pulled off the end of the tip. I have read, that the reason for this tip is to avoid, that the hook may catch or damage the remaining thread when it comes around the second time. I know that only a few rotary hooks got this tip. 

I have of cause checked timing and some other matters in order to fix this problem. One matter was to grind and polish this tip. It do get worse with thicker thread (I have tried Tex 70 and Tex 135 Amann Serafil). I know another user with another Dürkopp 291, that have used the machine without this tip and with no problems. And I have tried the same with some threads and fabrics, and I have not seen problems either. But I also have got some warnings about that from a sewing machine repair professional. I have also been told, that this hook have been made with specific differences, that may relate to subclasses. The original subclass of this machine is E1 and it is one of the early versions of the machine.

I have tried to measure the length of this tip when taken off in order to possibly compare the length with other users:


Do you know about the issue with this "Gegenspitze" and possible ways to fix it?

Edited 11 hours ago by Gymnast

[friquant]

 

2 hours ago, Gymnast said:

My problem is, that the thread is pulled hard by the take-up lever on this Gegenspitze before the thread finally is pulled off the end of the tip. I have read, that the reason for this tip is to avoid, that the hook may catch or damage the remaining thread when it comes around the second time. I know that only a few rotary hooks got this tip. 

Can you post an up-close slow motion video of the hook area as this is happening?

My usual approach to preventing the hook from catching on the thread when the hook comes around the second time is to retard the hook. It's quite predictable on the two machines I've tried this: Advance the timing and the hook grabs the loop of thread on the second time around. Retard the timing and the loop of thread is too far out in front of the hook point to be grabbed.

Rather than follow factory timing on those two machines, I found my own timing specification that is advanced enough that the thread can be pulled around the bobbin case without too much tightness, but retarded enough that the hook does not grab the thread on its second time around.

See this post for some background: https://leatherworker.net/forum/topic/131646-new-way-to-measure-and-visualize-hook-timing/

 

[Constabulary]

afaik the "counter hook tip" is meant for thinner thread at higher sewing speed. But I do not know how thin and how fast. So if the problem is solved w/o the tip then take it off al long as it does not cause other problems.

[nejcek74]

This is explanation from Cerliani:

which follows what your experience is and what Constabulary said, that with thicker threads the full gib is not always used. On my Pfaffs I have some hook variants with short and long gib for the same machine. They are variants for either A/B and C/D thickness classes and different gib goes with different hook.

Of course you can try and take this part away, but I am not sure exactly why. You wrote: "My problem is, that the thread is pulled hard by the take-up lever on this Gegenspitze before the thread finally is pulled off the end of the tip." Does it cause any real problem, like skipped stitches, broken thread or similar? Maybe you just need to make a little bit longer throw of the spring before the take-up lever? Have you compared hooks for different subclasses? Find if the differences is only in the gib or also in the other parts.

This is for DA N291, gib looks always long.

Durkopp also names it "Greiferspitze"