Set up of Juki LS-1341 type machine

[palvim]

Hello All,

I didn't want to hijack the Kobe 1341 thread hence writing here. I have a similar machine Juki LS-1341 copy. And I've had quite a bit of issues with thread jams and bobbin case being stuck etc. Sometimes to remove it, I've had to use some force. 

Problem is that I get very uneven stitch with 138 thread which this machine should easily handle. 

https://youtube.com/shorts/jjLYTC-UdCk?feature=share 

 

I'm wondering if someone could look through the timing and needle and hook position to tell if it is correct. Below are the three videos. 

1. Timing of the hook in relation to the needle

 

 

2. Position of hook when pickup lever is at 12 noon. 

3. The presser foot doesn't seem to move. Is that correct? 

https://youtube.com/shorts/VuLEKlz3f2k?feature=share

 

 

 

 

 

 

[DonInReno]

1 hour ago, palvim said:

3. The presser foot doesn't seem to move. Is that correct? 

The outer presser foot only goes up and down.   You’ll need material under the presser foot or it can just hang there and not look like it’s doing anything.
 

That’s the top of the leather?  To me it looks like upper thread is binding or getting twists in it which creates too much tension and pulls the knot to the top.   Make sure it’s threaded correctly.

 

Edited April 20, 2021 by DonInReno

[Uwe]

I agree with @DonInReno about the top thread possibly snagging or binding at times and causing trouble. Inspect your thread path starting at the spool and make sure it doesn’t get hung up anywhere. 

The normal stitches on your belt look very nice, actually, and I don’t see anything drastically wrong with your hook timing (nice video, by the way!) 

Sometimes the arm with thread guide holes gets pushed out of alignment with the spool, causing trouble. The thread should come off the spool straight up into a guide hole directly above the spool, like this:

 

Certain type of threads also have a tendency to unwind by themselves and fall down off the spool, causing it to get stuck under the spool. It’s easy to miss because you’re so focused on the needle area of the machine. A thread sock can help prevent that. You can buy special thread socks like in the picture below, or just use a piece of cut-off lady’s hosiery (a super elastic thin sock/pant, also called pantyhose) :

 

 

There are lots of other places where the thread might wrap itself around a post or something else, especially if the thread wants to twist and curl up around itself like your thread does in the take-up lever video:

 

Also, according the Juki LS-1340 manual (https://www.juki.co.jp/industrial_j/download_j/manual_j/ls1340.pdf) the thread should NOT go through that guide on the way up, only on the way down:

Edited April 21, 2021 by Uwe

[palvim]

Thanks Uwe! I managed to steal one of my wife's pantyhoses. It now seems that after playing a bit with the tension, I can get the top tension quite right. Bottom is right too for the most part however, you can see sometimes the knot shows up in the bottom. Not sure why that happens. 

Pic 1: Good stitch - see the stitch on the rightmost. 

Pic 2: Bad stitch - see the stitch rightmost pointed with red arrows. 

 

And I might add that this is with thread size 92 and needle 140. If I use thread 135 with needle 140 (which I believe should still be ok) the problem worsens. You can see that in 2nd pic on the 6th stitch from the right. That's on thread 135 with 140 needle. 

And the bad one. 

Edited April 21, 2021 by palvim
Added details

[Wizcrafts]

@palvim

When the position of the knots changes as much as your are it means something is interfering with the top or bobbin thread flow. I would take a close look at the top thread to see if it is getting twisted around the spool, or a thread guide. There may be debris inside the tension disks. Or, the thread might be lifting and then dropping into the tension disks.

Next, change needles and use a smaller needle for #92 thread. I find that a #19 works best with T90 thread and a #23 works best with T135 thread (both top and bottom). If the bobbin thread is smaller, I move down one needle size. Smaller needles make tighter holes that tend to stabilize the knot position.

Next comes the bobbin, the bobbin case and its tension spring. Pull out some bobbin thread and feel if it varies as you pull. You can rewind the thread after pulling out enough to learn if there is a problem with it. It could be cross wound on the bobbin. Or, there could be a small piece of shredded thread under the bobbin tension spring. Try reversing the direction the bobbin feeds through the slot in the case.

Next, check the hook for burrs. Then adjust the bobbin case opener lever so it pulls just enough to let the top thread clear the tab on the throat plate and doesn't hold too long as the thread comes around the case. Listen for any snapping sound as the thread goes around the bobbin case and shuttle. It could be getting hung up due to the timing being off.

Last, try a different spool of thread, including winding a fresh bobbin with it.

[Uwe]

The presser feet also play a role. Your left-only presser foot may not hold soft or thin leather down quite enough to make consistent stitches. If the leather pulls up as the machine tries to pull the knot into the material, then the knot will stay on the bottom. This may happen only occasionally as you encounter soft or thin spot in the leather. Leather is not as uniform in thickness and density as man-materials like vinyl. 

When you get a chance, perhaps show us a close-up video of your machine sewing that stich line, veeeeeery slowly.

There are reasons to choose different feet for various sewing projects, to get closer to an edge, to see better, etc. The “best” feet for consistent stitches are double-toed feet that hold the leather down very close to the needle. 

Very thin leather of course is also among the most challenging because there just isn’t a whole lot of material for the knot to pull into. It doesn’t take much variation to have the knot become visible on top or bottom. Thick leather or material is much more forgiving in that regard.

When I test sew a new material/thread/needle combo, I usually sew extremely slow while turning the tension knob to increase the top thread tension until I see the knots getting pulled to the top. Then I back off the top thread tension again until the top knot disappears into the material and that’s my tension setting for that particular combo.

 

Edited April 21, 2021 by Uwe

[palvim]

@Uwe

Here is the video from the side. Unfortunately I don't have a speed reducer and this is the slowest it'll go. The leather is almost 7mm of veg tanned leather. Anyways, in the first video the stitching came perfect on both sides. But see the second video shot immediately after the first one. And there the bottom stitch turned out horrible. It's very hard to trust the machine. 

 

 

Edited April 21, 2021 by palvim
Added details

[Uwe]

Tough one, it works perfectly until it doesn’t. Next move: experiment.

My next suggestion would be to try a larger needle. The machine appears to pull the knot into the material just fine, until it doesn’t.  (The machine does appear to struggle a little pushing the needle through the leather.)

A larger hole might help makes things easier for the machine and provide more consistency.

The tip of the needle also plays a role. If you’re using a fabric needle with a regular pointy tip, you may get a different results compared to a leather needle with a cutting knife-edge tip.  The knife-cut hole in leather has less of a tendency to close back up again, making it easier for the knot to get pulled into the material. The knife edge makes it easier for the needle to slice through the leather, allowing you to use larger needle. Leather needles tend to make clean holes with clean edges, fabric needles sometimes tear a rough-edged hole out the back, which may resist the knot more.

Some may protest that there’s some chart somewhere that says a size 140Nm/#23 needle should work fine with size 138 thread. These charts work well in some circumstances, in others they don’t. Use the chart as a starting point and then make adjustments as needed. Whatever works, works. If the needle in chart doesn’t work, change it. Leather type and thickness, machine design, moon phase and The Force may play a role as well. There’s no needle police coming after you for using a needle that’s not in the chart. 

Sewing is an art and science. The needle chart is part of the science, the art comes in when you ignore the chart. Of course it’s not quite that simple in real life.

 

[palvim]

I'm just wondering if the thread knot always shows up in the bottom, could it be that the bottom thread is getting stitch somewhere in its path as @Wizcraftswas suggesting? 

I know I had to force the machine to open the thread jams. Could it be that bar that pulls the bobbin case back to let the thread from the throat plate notch? I guess that's called bobbin case opening lever. I had to force the case through this lever by force. May it moved just a tiny bit. But in that case shouldn't the top thread be stuck meaning the knot should appear on the top instead of the bottom? 

May be a stupid question. How to check for burrs on the hook or elsewhere? 

[Uwe]

Yes, it is possible that the top thread snags somewhere as it travels around the hook, that was the focus of the Kobe 1341 topic.

In general, it’s almost never a good idea to “force” though a thread jam. The only sensible thing to do when the thread gets jammed is to stop the machine, open the cover and un-jam the thread gently by pulling it out with a tweezer and/or gently rocking the hook back and forth to loosen the jam.  

Going forward you’ll to make it VERY clear whether the knot is on the top or bottom, especially in pictures. Use two layers of leather that face the same direction so that there’s a very clear visual difference which side it top and which is bottom. Then always stitch from the top side. I think several of us got confused early on when we looked at photos of your stitches. 

Take another look at the stitch cycle video, and if possible, show us what that exact same sequence looks like on your machine.

 

As for the bobbin case opener detail, here’s another video that goes over the function and adjustment (and possible bind issues) of that mechanism.

 

 

[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? 

[palvim]

I also notice that when the bobbin case opener is put in the right place more or less the machine jams somewhere and I can't rotate the flywheel further. Is the bobbin case installed wrongly? 

 

 

[Wizcrafts]

For the time being, I would back off the position of the case opener until the hook turns freely. There could be some thread or other debris caught in the gears that drive the hook. Or, the opener might be pulling back too far. It only needs to make a slight movement on the bobbin case so that the top thread clears the tab.

[palvim]

I've more or less got the machine to be where it was before. 

Hook timing seems to be ok

Bobbin case opener a little better. 

But the same problem persists. 

I'm really curious if all parts that are listed in the parts manual need to be for 1341 to use the 1341 hook? Could it be that the machine actually is a 1341 but just has the wrong hook? The company specifications says the following. 

 

Cylindrical lockstitch machine with compound transport and high walking foot. The model is destined for medium and heavy sewing. Compound transport, large stroke of needle bar and foot lifting to 16 mm facilitate technical sewing. The hook is larger about 30% and it is especially useful in case of technical sewing with thick threads. The diameter of cylinder is 72 mm. There is energy-saving motor which saves even 70% of energy.

For this model of machine JUKI parts are suitable.

We offer assembled, ready to work set including:

head, motor, top table and stand, a drawer, additional accessories, operating manual

Technical parameters

Type of stitch	Flat lockstitch
Type of transport	compound
Direct drive	no
Maximum length of stitch	9 mm
Maximum speed	2000 spm
Maximum foot lifting	16 mm
Stroke of needle	36 mm
Size of hook	enlarged
Lubrication	open
System of lubrication	manual
Automatic needle positioning	no
Automatic thread cutting	no
Automatic foot lifting	no
Automatic bartacking	no
Automatic walking foot	no
Automatic wiper	no
Automatic nipper	no
Control panel	no
System of needle	DPx17
Thickness of thread	#10
Clearance under arm	260 mm
Built-in LED lamp	no
Controlled by smartphone	no

 

 

[DonInReno]

How interesting this problem has become!

We don’t know exactly what kind of machine this is.

We don’t know what size thread it’s designed to sew.

We don’t know what’s binding up the hook.

We still don’t know what is causing the original tension issue, although it’s probably related to the hook binding up.

I’d say you should find a repair shop to clear the hook, then get the machine to sew correctly with thinner thread, before trying to do anything more with thick thread.    The hook has to be completely cleared of what’s jammed it up. 

[palvim]

I guess that's the right thing to do now. It seems we've tried enough. Now let the repair shop try. I'll be going the week after next. I'll update here. But I really hope this machine can handle 135 thread easily otherwise, I'll ask them to order the parts for the 1341 machine and install that. I counted from the parts manual and it's about 13 parts. 

I can say enough how grateful I am for all the help I've received so far. Thank you.