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.