Set up of Juki LS-1341 type machine

[DonInReno]

Yes, I should have asked in a better way which side of the leather was up.  Disregard everything I said.

[palvim]

I'm so sorry for confusing you and wasting your time by using both layers looking the same. So sorry for that. Next time I'll definitely used two different looking leathers. 

I checked the bobbin case opening cycle and I think it is definitely wrong. I can distinctly see and hear two clicks. 

I guess I need to pull the bobbin case opening lever back so when the thread is just about to come out of the throat plate, the lever is already touching and pulling the bobbin case protruding thing  to the middle of the throat plate notch. Am I correct? 

 

 

[Uwe]

I see the thread snagging slightly as it’s trying to slip into the passageway under the throat plate, and a second time when it’s trying to cast off the hook gib. The thread take-up leaver is trying to pull up the thread, but the hook hasn’t let go if it yet.

The upper shaft with connected (non-adjustable) linkage for the needle bar and take-up lever determines the timing of everything else in the machine. 

So, based on that video I’d say you need to do two things:

1. Advance hook timing a little bit to make it arrive at the needle sooner. This will also make the hook let go of the thread a moment sooner. Your top thread snags momentarily as it’s trying to get cast off the hook.

2. Your bobbin case opener is too late in starting pull back the bobbin case. The thread has already force-slipped into the passage when the bobbin case opener is just starting to touch the bobbin case. Ideally, by the time the thread needs to slip into the passageway under the throat plate, the bobbin should already be pulled back into the center of the cutout under the throat plate.

The arrow in this still image points at your hook cast-off gib, the little finger that point up. Your thread gets stuck at the bottom of it. 

 

My stitch cycle video above does show both of those somewhat critical moments. The bobbin case opener video show the proper adjustment of that mechanism. Details matter. 

If the thread snags at any point during the stich cycle, more thread may get pulled from the spool and the thread take up lever has no chance of pulling the knot into the material.

In your case the hook timing and bobbin opener timing is off just a little bit, which may explain why it sometimes works fine, and sometimes it doesn’t. To make it work consistently, you have to adjust the timing to be in the sweet spot, not teetering on the edge of failure.

Just to illustrate the cast-off problem, this video shows the too-late-cast-off problem on one of my other machines. Advancing hook timing solved the problem in my case.

 

By the way, according to the Juki LS-1340/1341 parts manual diagram ( LS-1340-LS-1341_P.pdf), you appear to have the hook assembly for the LS-1340 (hook assy. 12 in the diagram) , which is the smaller capacity hook for smaller thread sizes (up to size 92). The large capacity hook (hook assy. 1 in the diagram) is for thick thread (up to 138) and has a bobbin cap. Clone manufacturers often mix and match parts from different versions of the original to come up with their own clone version.

This hook design difference may contribute to your troubles making size 138 thread work consistently, because it’s really beyond the spec for that hook assembly. However, with a little fine tuning, you can likely make it work.  

 

Edited April 22, 2021 by Uwe

[palvim]

Hi Uwe, 

Luckily, I might have the other hook assembly. I had asked for a table with wheels but they didn't send me that table. In exchange I asked for this hook to make my machine similar to Techsew's machine. You mean this hook in the picture is for size 138 thread? I didn't see in the manual about the hook sizes for thicker and thinner thread. Could this bigger size hook manage thread size 207 ? That would really be super!! I will never need to go above that. 

But I guess I'll have to take it to a service guy here in Sweden. Changing the entire hook assembly is a little out of my area of competence. I might screw it up even more and then I'm really stuck. 

But ok, at least it seems like we have found the main reasons why it doesn't work as it should. That's excellent. I can't thank you Uwe, Wizcrafts and DonInReno for your time to help me out. I'll take it to the service guys here and then update if this was the thing that fixed the issue. 

 

[palvim]

I just noticed that the existing bobbins don't fit into the new hook. Is there a need to change the pickup lever if hook was to be changed to the new one? Or is it a one to one replacement and no other parts need to be changed? 

[Uwe]

There are several parts that need to be changed over to use the other hook. Check the parts diagram. Every part that is listed separately for the 1340 vs 1341 is involved. It’s not a simple task, more like major surgery. I’d recommend trying to make the current hook work reliably before undertaking that project. That hook by itself isn’t very useful to you. 

[chrisash]

Uwe Many thanks for the above video, i only had a very vague idea of the Bobbin case opener function, your video is the perfect explanation, I doubt I would have figured it out the reason for it in a hundred years

[palvim]

1 hour ago, Uwe said:

There are several parts that need to be changed over to use the other hook. Check the parts diagram. Every part that is listed separately for the 1340 vs 1341 is involved. It’s not a simple task, more like major surgery. I’d recommend trying to make the current hook work reliably before undertaking that project. That hook by itself isn’t very useful to you. 

Hi @Uwe

I understand. Pity that they sent me a machine that is not suitable for 135 thread. 

I guess I'll have to try and give it a shot to advance the hook timing and the bobbin case opener. 

I'm quite clear about the bobbin case opener setting. However is the hook timing for this machine seems a little complex. Is it the same video you shared Uwe in the Kobe 1341 thread? 

Edited April 23, 2021 by palvim

[Uwe]

It’s not very difficult to make small hook timing adjustments. I just tried it out on my Juki LS-341. This video is NOT a full hook timing video! It’s just shows you how to quickly make very subtle adjustments to the hook timing.

 

Edited April 23, 2021 by Uwe

[palvim]

Thanks @Uwe

I just opened the throat plate and bottom plate to check my timing and to me it looks just right without doing anything to it. The feed lever is at 0. The hook also seems to meet the 1.7mm line from top of the needle hole just while it is coming up. 

 

Did I miss something? Could you check the video?