Class 26 Loose Stitches/Loud Noise

[LiftPig]

Good morning everyone,

I'm having some trouble with my Class 26.  I'm usually running 138 or 207 top and bottom through 8-16 ounces of firm veg tan.  I use a 23 needle for 138 and a 25 for the 207.  I'm getting inconsistent stitch tension and the occasional balled up knot/loose stitch that isn't pulled up through the piece.  This is especially true going around any type of corner but as you can see in the pictures it happens in the straights a lot too.  The pictures below are 207 through 8 ounces of veg on a 25 Schmetz tri point needle.  I've cranked down the tension until every knot is on top and it still happens.  I've cranked down the pressor foot as far as it goes and it still happens.  I've raised the needle until its barely in the leather before making a turn and it still happens.  What's most frustrating is that it's so random.  I'll get two or three stitches that has too much top tension, then two or three that have two little.

I spoke to a guy who is well established as knowing these machines well and we worked on tension, bobbin tension, cleaning out the tension discs, changing needles, rethreading the machine, different threads, looking at timing, and technique.  We were on the phone for about three hours and at the end he said "I can't think of anything else to help you, you might be screwed".  

One thought I have is that when the thread pulls from under the bobbin case it makes a loud popping sound.  I have a video of it but it's too large to embed here.  I've scoured the internet looking at videos of sewing with a 26 and with only one exception, nobody's machine makes that noise.  It seems logical in my brain that the top thread getting caught under the bobbin case is going to make a tension issue as the take-up lever raises.  I've taken apart the race to look for debris but haven't found anything.  The machine is well oiled.  Could this be my culprit?

I'm at a loss.  I do know that I have a backlog of orders and a machine that's making loose stitches that have to be-resewn.  I am extremely grateful for any help or insight.

Cheers,

Jordan

Edited May 16, 2023 by LiftPig

[kgg]

38 minutes ago, LiftPig said:

I'm having some trouble with my Class 26. 

How long have you had the machine? Have you contacted the Leather Machine Co? There was recently another member with a similar problem.

kgg

[LiftPig]

Hi KGG

I've had the machine about 18 months.  I always thought the noise was the spring on the third tension disk (check-spring?) resetting and the knots were something I was doing.  I slowed way down, watched the spiral exercise videos on YouTube, practiced a lot, and was very careful about technique and still have issues.  It wasn't until the gentleman I spoke to on the phone said he heard the twang and had never heard such a noise coming from a 26 that I started investigating where it came from.  

I did look through the thread you linked - his noise was some sort of squealing coming from the shaft - mine's something else.

I haven't talked to LMC yet.  My work schedule has me working when they're open.  The good news is my schedule changes in a couple weeks and I'll have Friday's off to call them.

Here's a link to the sound: 

 

 

Edited May 16, 2023 by LiftPig
Adding movie

[Burkhardt]

Are your issues mostly happening using black thread and in the pictures are they of the same size thread in both pics top and bottom? Also are you using 2 different color threads when you have problems?

[Wizcrafts]

I think that the top thread is getting pinched as it exits the shuttle and bobbin case. It looks like the case opener lever isn't pulling back the bobbin case to give its tab some clearance for the thick thread you are using. Try setting the opener arm so it pulls the case backwards as the thread moves around and past the bobbin case. Also, play with the check spring travel and position settings to get a little more slack in the top thread.

[kgg]

18 hours ago, LiftPig said:

Here's a link to the sound

Looking at the video what I see is the bobbin thread appears to be under tension with no slack as the thread is being slipped pass the tip of the hook about the 5 o'clock position. A couple of things I would check is the needle to the hook timing, worn / sticky parts in the bobbin release mechanism, damage to the notch in the needle plate and hook assembly.

A couple of good video's to review:

i) The stitch cycle of a Juki LS-341 by @Uwe gives a really good demonstration of how the the bobbin release should work (1:37 of video)

ii) Cobra Class 26 needle hook timing inspection and reset procedures by Al Bane

kgg

[Tequila]

I’m with kgg on this.  Maybe these manuals will be of some help

Juki LS-341N InstructionManual.pdf

Juki_LS-341N_Engineers_Manual.pdf

[LiftPig]

13 hours ago, Burkhardt said:

Are your issues mostly happening using black thread and in the pictures are they of the same size thread in both pics top and bottom? Also are you using 2 different color threads when you have problems?

The thread is same size top and bottom - 207.  It happens with all threads pretty equally.  I did once think it was a black thread issue (of which there are many) since most of my sewing is black thread but that's not the case.  

 

2 hours ago, Tequila said:

I’m with kgg on this.  Maybe these manuals will be of some help

Juki LS-341N InstructionManual.pdf 653.29 kB · 2 downloads

Juki_LS-341N_Engineers_Manual.pdf 738.97 kB · 2 downloads

Wow these are great manuals.  Why aren't the ones that come with Cobra's this good?  Thank you so much!!

 

 

Wiz and KGG - Thank you for the advice and videos!  Looking at the 341 video compared to mine and breaking them down frame by frame, mine is under way more tension.  I'm betting that the take up spring and/or bobbin case opener are mal-adjusted.  I'll work on those adjustments and report back.

 

 

[kgg]

1 hour ago, LiftPig said:

Wow these are great manuals.  Why aren't the ones that come with Cobra's this good?  Thank you so much!!

Clone machine manuals vary greatly with the Sailrite manuals being some of the best I have seen while others well lets say they are less then. Some I have seen were very poorly translated, almost unreadable to almost English. Generally clone owners have to track down what their machine is cloned after to get the proper manuals or find decent youtube video's. 

kgg

[LiftPig]

On 5/16/2023 at 11:30 PM, Wizcrafts said:

I think that the top thread is getting pinched as it exits the shuttle and bobbin case. It looks like the case opener lever isn't pulling back the bobbin case to give its tab some clearance for the thick thread you are using. Try setting the opener arm so it pulls the case backwards as the thread moves around and past the bobbin case. Also, play with the check spring travel and position settings to get a little more slack in the top thread.

Update:

I moved the bobbin opener back as much as I can without causing a bind.  The manual is really vague as exactly how to set it so I used @Uwe method of setting the tab in the middle of the slot when the thread reaches 3 o clock and then a touch more.  I also changed the swing and tension of the check spring to give the top a little more throw.  I would say the noise of the thread getting caught beneath the bobbin case has reduce about 50%.  I did a few test stitches that looked pretty good but then had to leave for work.  I'll test some more today.

@Wizcrafts you mention in a few other threads advancing the timing a little bit (a couple degrees) when someone else described a similar problem.  Would that be helpful?  I have my timing set in the method that @VanPlew describe in their youtube video.  I recall seeing a post from @Uwe saying how he likes to time based on hook position rather than a distance above BDC but now I can't find it again and I don't remember which position he mentions.  I think it's having the hook tip at 7:30 when at BDC but I can't recall exactly.

 

The aforementioned @VanPlew video:

 

[LiftPig]

Here's my (I think) resolution post for my own reference and for anyone else running into problems who don't want to go through all the posts above and just want to skip to the weenie.

I ran several pieces yesterday with 138 on a #23 needle through 8 ounces of veg tan married to 4 ounces of soft oil tan with contact cement and got good stitches and a quiet machine.

1.  I shortened the throw of the check spring by loosening the screw on the underside of the device and moving the curved piece of metal clockwise about 20 degrees.  The video from @Uwe posted above explains the proper position.  The screw isn't obvious, it's not the two screws on the front of the disk, it's the one on the bottom going through a curved slot in a piece of metal that looks like it can be adjusted - you'll need to get your eye level below the disk and look upwards. This gave the top thread more slack coming around the bobbin case so it follows the contour of the case smoothly and at an even rate. The video for that is a couple posts above.

2.  I adjusted the bobbin case opener to allow just enough room for 207 to pass through without binding up and no feeling of binding on the machine when sewing.  The video on how to do this is below.  Make sure when you think you've got it you turn the hand wheel slowly and feel if it is a smooth travel all the way around.  If it feels like it's binding, you're probably adjusted too tight and you need to back that adjustment off a little more so the bobbin case opener isn't straining as the machine works.

3.  I retimed my machine so that I'm advanced of the recommended 1/8" above BDC for my timing moment.  I tried setting my timing so that the tip of the hook was at 12 o'clock when the arm was at it's very top and ended up skipping stitches.  I backed to about 11:00 and that seems to be the sweet spot for my machine.  I'm not sure where that relates to the needle above BDC because I didn't take the feed dogs off to measure precisely. It's around 3/16"-7/32".  That video is below as well with the following disclaimer:  Uwe mentions adjusting the timing belt.  He has since posted that was the incorrect adjustment and was not the correct solution.  The correct adjustment is the hook timing.  Don't mess with the timing belt.

 

A couple tips:

1.  The Class 26 is a Juki 341 clone.  There's a paucity of videos and info about the 26 but a bunch of stuff about 341 and Tacsew 1563.  As best as I can tell they're identical in all the ways that matter.

2.  Start with adjusting your hook timing.  I did this backwards and started with the check spring adjustments, then the bobbin case opener, then the hook timing.  Go in the opposite order.  In my case the hook timing was the big winner, though the other two needed a bit of refinement too.

3.  There's a second component to the hook timing, and that's the needle bar.  It's mentioned in the video by @VanPlew above.  If your timing is thrown off because you hit a snap or something, you'll probably need to adjust this too. 

4.  The manual that came with the Class 26 is pretty bad.  A couple posts above @Tequila shared some much better manuals.  Go download them.  

 

Thank you!!! to @Wizcrafts, @kgg, @Burkhardt & @Tequila for their help and to @Uwe for taking the time to create videos that we can all watch and learn from.  

 

Bobbin Case Opener Adjustment

 

Timing Adjustment:

Please note, Uwe mentions adjusting the timing belt.  He has since posted that was the incorrect adjustment and was not the correct solution.  The correct adjustment is the hook timing.  Don't mess with the timing belt.

 

[TomE]

Thanks for the summary. Good info that will help me navigate future (inevitable) challenges. 

[Tequila]

@LiftPig it’s too bad that you had all those problems, but on the bright side you now know that machine well and if something ever comes up again you’ll be confident you can fix it. Thanks for the videos and keeping us up to date.