Kobe 1341 not bringing up knots.

[palvim]

On 4/13/2021 at 8:08 PM, Uwe said:

I still think the issue has to do with hook timing and not needle size, although it may be a combination of factors. 

It looks to me like the hook arrives a little too late at the needle. This causes it to be slightly out of synch with the the take-up lever movement. The still frame below shows the moment where I think more thread gets pulled from the spool. The thread is taught everywhere and the check-spring is overpowered and maxed out. The thread take-up lever has already started going back up at this moment. At this point it does not matter what tensions setting you have dialed in, thread will get pulled from the spool no matter what. Every millimeter of extra take-up arm movement pull two millimeters of extra thread from the spool. That excess thread will later prevent the knot from getting pulled into the material.

 

This still frame below is taken at the moment the needle is at bottom dead center. The tip of the hook appears to be near the 6:30 o’clock position. It really should be near the 7:30 o’clock position (needle is at the 9:00 o’clock position)  

 

I made a quick handheld video showing the stitch cycle on my Juki LS-341 in a slow motion hand-turned stitch. Hopefully it will allow you to compare my stitch cycle timing with your machine. 

 

My recommendation would be to advance hook timing by about “5 minutes on the clock face” and see if it helps.

I am having similar issues and I have the same machine just a different brand. I had got the thread jams and all kinds of issues with the bobbin case being stuck etc. Somehow I managed to unjam and get the machine sewing again. This video is so helpful. I see that my hook point is more at 11 O' clock rather than 12 O' clock at the lever being in its highest position. I am wondering how to fix the hook point to be at noon. Could you point me to some instructions Uwe? Thanks. 

[Uwe]

(I can’t remove the accidentally embedded/deleted video above, please ignore)

The Juki LS-341 manual is the main reference for adjustments. Here’s the full PDF:

ls341n.pdf

Here’s the relevant section:

 

The picture below shows the three screws that hold the hook driving gear to the shaft. Follow the manual for adjustments and screw tightening sequence.

Things to keep in mind:

Keep the teeth of both gears engaged at all times. The gears are very likely matched pairs, meaning they are made to mesh with specific opposing teeth for optimal smoothness. 

Push the driving gear gently to the left to fully engage the teeth before tightening the screws again. If the teeth are not fully engaged (touching), you will have play in the driving gears, meaning you will be able to wiggle the hook back and forth. Ideally the hook should nice and snug with very little play.

This hook driving gear design on the Juki LS-341is nearly the same as on the Adler 67, the only real difference being the number of clamping screws on the gear itself. The two machines are very different in many aspects, but this driving gear detail and how to adjust it is very similar. You can watch this video on hook timing for the Adler 67 to get an idea of how those gears work, starting at the 3:50 mark.

Note: The Adler uses only two screws, the Juki uses three screws and a specific screw tightening sequence!

 

 

Edited April 20, 2021 by Uwe

[DonInReno]

Patty,  Maybe bobbin tension was talked about more and I missed it - at the risk of beating the dead horse here's a way to eliminate that as a cause.   Because bobbin adjustments are so subjective, it's not uncommon for us to be helping someone who thinks they have adjusted the bobbin tension correctly only to find out it's way too tight.

I'm assuming since the bobbin is loaded from the top that the bobbin case is built in and only the bobbin itself is removeable?   Over a discussion forum its really hard to describe and judge the correct tension since the traditional way of judging a starting tension involves a removable bobbin case hanging from the thread tail.  

I measured that thread tension and it's about 30g.   Putting 5 loonies or 5 US quarters in a baggie and hanging it by a thread gives you an idea about the amount of tension you should have coming out of your bobbin tensioning spring.  4 loonies is not enough - that's the equivalent of the bobbin case falling to the floor on it's own.  7 loonies is definitely too much.

If nothing else this will help those of us who worry bobbin tension hasn't been ruled out. :-)

You've been sewing heavy fabric with this machine - does the bobbin thread pull up ok in the fabric?  A picture of the bottom thread in fabric would be nice.  (this helps to rule out needle size as being the culprit since needle size isn't as big a deal with fabric - if the stitch looks great in fabric and crappy in thick leather that suggests needle size is still too small in leather.)

Is this the same machine that says made in Japan, but the box said made in China?  I have a few parts with similar pedigrees - I have no idea if they are Japanese, were assembled by Japanese, were inspired by Japan, or are just mislabled.  :-)

Hang in there - the more things you can rule out the closer you're getting to smooth sailing!

[DonInReno]