Tension question - Class 26

[Landcruzer94]

I have an issue with setting the tension on my Class 26.  Here is what I'm working with

Fresh size 20 LR needle

92 thread

2 pieces of 3-4oz leather

Threaded and bobbin loaded according to LM Co's instructions.

 

When I'm sewing I have the tension adjusted to bury the knot equally between both pieces of leather, but every time I stop and turn a corner (1/4" above BDC) the top thread pulls the bottom up and leaves the knot exposed. Doesn't matter if I use the foot pedal to raise the foot or just turn the piece under pressure the same thing happens.  If I lower top tension to help the corners then all the knots start showing on the bottom.  There doesn't seem to be a middle ground that will solve everything.  I'm only adjusting the main tension knot, everything else is factory from Leather Machine Co.  Sewing size 69 thread didn't seem to be an issue with a size 18 needle.

 

I also note that the tension mechanism seems to be making some extra clang noises that I don't hear on others machines on YouTube.  

The final cycle is done by hand to show the kind of tension that's on the top.  It doesn't feel right to me so maybe others can confirm.

[JREESER1]

Make sure the needle is starting the up-stroke, before you make the turn. (even just barely starting up)

[Landcruzer94]

1 minute ago, JREESER1 said:

Make sure the needle is starting the up-stroke, before you make the turn. (even just barely starting up)

Yes it's 1/4" or so above bottom dead center before I do

[Constabulary]

when I make turns my needle tip is still in the material the way that I see needle scarf - maybe worth giving it a try.

BTW - have you opened your slide plate / hook cover and watched the thread when it slides around the hook? Maybe it keeps hanging somewhere maybe on the bobbin case opener or the hook needs some adjustment - just a guess.

Edited August 30, 2024 by Constabulary

[kgg]

11 hours ago, Landcruzer94 said:

I also note that the tension mechanism seems to be making some extra clang noises that I don't hear on others machines on YouTube.  

Maybe you might want to send Leather Machine Co. an email with the video to determine what the clanging noise is.

kgg

[TomE]

To narrow the possibilities, I would test with thin veg tan leather and a TRI point needle.  I am interested in learning more about this symptom.  I  mainly sew heavier leather with #138 thread on a Class 26.

[Landcruzer94]

Thank you all for the suggestions.  I tried the suggestion by TomE, switched to veg and a diamond point needle and unfortunately did not remedy the issue.  I did however uncover the source of the sound I referenced earlier.  The slapping sound is because of the top thread binding within the shuttle(?) below as the string goes around.  The below video shows the two slapping sounds, first as the thread goes over the first gap, second as it binds down below and finally the takeup spring slaps upward as it breaks free.  This does not sound/look normal to me and may be the source of at least some of the tension issues that I have.

 

 

9 hours ago, Constabulary said:

when I make turns my needle tip is still in the material the way that I see needle scarf - maybe worth giving it a try.

BTW - have you opened your slide plate / hook cover and watched the thread when it slides around the hook? Maybe it keeps hanging somewhere maybe on the bobbin case opener or the hook needs some adjustment - just a guess.

You may be on to something, per the video I just posted.

[Constabulary]

I have not worked on machines with this type of hook for a loooong time. I guess its a thread take up lever or hook timing issue (or both).

 

[Wizcrafts]

First of all, I see thread that is bound onto the bobbin hold down tab. Free that thread before you do anything else! There should never be thread trapped like that!

After freeing the thread from the tab, check the hook timing vs the eye of the needle on the upstroke. A properly timed hook will intersect the needle about 1/8 inch above the eye and sill be within the scarf cutout. Many times, a late hook will cause that snapping sound. Advance the hook a bit the loosen the thread loop.

The check spring comes into play here. If the travel is too long, the top thread stays taut longer than necessary. Before you change the bottom stopper, try moving the screw in the curved slot to the right end of its travel. If that doesn't help, loosen the screw under the bottom stopper bracket and move it so the spring only moves a little past when the needle makes contact with the top of the leather. This adds slack thread and reduces the tension as the thread goes around the bobbin case.

[Constabulary]

Wiz, I think the bobbin thread belongs there. Thats what the gap in the bobbin retainer is for. Other machines have it this way or very similar too

[Wizcrafts]

7 hours ago, Constabulary said:

Wiz, I think the bobbin thread belongs there. Thats what the gap in the bobbin retainer is for. Other machines have it this way or very similar too

That's a first for me. I have never had a machine that threaded the bobbin retainer tab like that.

[kgg]

1 hour ago, Wizcrafts said:

That's a first for me. I have never had a machine that threaded the bobbin retainer tab like that.

The Cobra Class 26 is a hybrid clone of the Juki LS-341 and what appears to be bobbin assembly similar to that used in Durkopp Adler 867 ( https://www.youtube.com/watch?v=jpzfM0bsd6g )

kgg

 

[Landcruzer94]

Hi all, thank you for the responses!  I stumbled upon a thread from last year that showed the exact situation creating the binding/noise below the bobbin case.  Surely enough I was slightly out of time: 

 I took a few hours this AM and adjusted the hook timing to spec, made sure the bobbin case opener was adjusted properly according to what I'm seeing on the videos within that thread.  The noise is gone and stitches look great.  The only thing I still have is the knot poking up when turning a corner.  The check spring was the last question mark for me that I've been trying to understand the adjustments for.  The only thing I've touched on it has been the bottom U-shaped limiter so far.  @Wizcrafts I'll take a look at some of those adjustments you suggested.

I'm confirming there is absolutely no tension on the upstroke where I would stop and make my turn.  I watched inside as I turned to see if there was anything binding and I'm not seeing anything.  At this point I'm suspecting either my needle is pulling the knot upward as it's coming out or there is some loss in tension on the bobbin, which wouldn't make any sense since it's a constant setting not impacted by anything other mechanisms, right?

 

[Landcruzer94]

Okay, another 8 hours or so worth of fiddling and I can say that the machine is working great (in the forward position, see belopw) and I completed a flawless spiral while being able to lift the presser feet to make 90deg turns!

Some things I noticed:

I set my machine to the timing specs EXACTLY in both Al Bane's and @VanPlew 's video (two separate attempts to reset timing) I still get that Twang sound as the thread gets hung up between the hook and the inner hook race, you can actually hear it in his video too (Timestamped in the link). I feel that this is wrong after hearing what a machine sounds like with no interference. 

I ended up going to the Juki manual and set my needle bar to the specs they note, but for some reason when aligning the hook to the center of the needle at their spec of 2.4mm above BDC, the hook ends up at about 2 o'clock when the takeup lever is at TDC.  I retarded the hook back to 1130(ish) after seeing how Uwe's machine was set up in his video and this was the fix.

The factory setting of the hook assembly "saddle" was outside of Juki spec, so I also shifted that closer to the needle.

The only issue I now have with the machine is that the reverse stitches don't exactly align with the forward, but I think I may need to mess with the feed dog height and research where others are hitting the reverse lever in the stitch process.  If the hook timing doesn't alter that at all (which I doubt it does) then it's probably user error.

 

Thanks everyone for the advice!!

 

[TomE]

Thank you for all this information, @Landcruzer94.  I will work through it carefully as I become more familiar with the Class 26.  Which Juki manual are you working from?  LS-341?  LS-1341?

My first machine was a Class 4 that I knocked out of time shortly after I bought it.  Uwe's video on timing the 441 type machines was a great help.  

Edited September 2, 2024 by TomE

[deboardp]

I have a LM 26 and have the same problem. I'm not doing leather work any longer, but if I get back to doing some, I will refer to this thread. I know that LM doesn't know how to deal with the clanging noise, and they suggested things that I think made it worse. Of course it's a timing issue. Their head tech had me try things sort of like mechanics do, change a part or a setting, see if that fixes it.  It's better to know how to troubleshoot rather than do that. Figure out the problem, and then fix it. These adjustments only make things worse if we're guessing. We need to be smarter than that. 

Your videos are great quality!

[kgg]

15 hours ago, Landcruzer94 said:

Some things I noticed:

In your first video when the machine was under power the noise not the dinky noise but the rough cranking noise did you get that straighten out? Was that caused by a dry speed reducer bushing and over tight belt? A video with the machine under power would be nice.

kgg

[Landcruzer94]

2 hours ago, kgg said:

In your first video when the machine was under power the noise not the dinky noise but the rough cranking noise did you get that straighten out? Was that caused by a dry speed reducer bushing and over tight belt? A video with the machine under power would be nice.

kgg

The slow grinding noise? Sounds like Owen from Planes, Trains and Automobiles? 

  Believe it or not that's from the servo motor that they're putting on these machines.  The motor unit itself is smaller and I'm assuming the same power as other motors, but compared to the servos on my CB3200 and Yamata 810 it's a clunky mess.  The two aforementioned machines have a silky smooth run up, very low speed capable and are super quiet.  This motor has a very touchy pedal that--while it can go slow--is either on or off.  I get that it has the control unit for EPS, but if I had an extra servo motor I'd swap it out in a heartbeat.  On top of that the motor pulley is slipping, causing a harmonic resonance and I have rubber dust all over the belt train.  I've tried to tighten it briefly as I've been messing with the other bits, so now that I'm done I'll look at that deeper.

[Landcruzer94]

17 hours ago, TomE said:

Thank you for all this information, @Landcruzer94.  I will work through it carefully as I become more familiar with the Class 26.  Which Juki manual are you working from?  LS-341?  LS-1341?

My first machine was a Class 4 that I knocked out of time shortly after I bought it.  Uwe's video on timing the 441 type machines was a great help.  

The manual I used specifically was the juki engineers manual PDF from the thread I linked in an earlier post, it's for the 341N.  Being that they use a different (bigger?) bobbin than the 26 there may be some differences and probably why my hook position was off when I followed the first set of their alignment instructions

Here is an after video so you can see and hear the difference.  Im sure there's maybe a liiiiittle bit more headroom to adjust, but I'm satisfied with the way it's sewing. 

 

[kgg]

5 minutes ago, Landcruzer94 said:

Here is an after video so you can see and hear the difference.

A lot better. Glad you got that pretty well solved.

kgg

[Landcruzer94]

17 hours ago, TomE said:

Thank you for all this information, @Landcruzer94.  I will work through it carefully as I become more familiar with the Class 26.  Which Juki manual are you working from?  LS-341?  LS-1341?

My first machine was a Class 4 that I knocked out of time shortly after I bought it.  Uwe's video on timing the 441 type machines was a great help.  

Uwe completely saved my ass with my CB3200 thanks to the same video! This community is awesome