HELP! Bobbin thread on top only when start sewing

[Relative]

Hello all,

I have had this issue for a long time.

I can sew normally fine however when I stop mid stitch is when the problem happens. I take my foot of the pedal and the needle gets buried due to the needle positioner. I do not touch the work or make any changes, no lifting the presser foot, nothing. I then begin sewing again and for the few 1 - 5 stitch the bobbin thread gets pulled to the top as shown in the images below.

To my knowledge I have tried everything.

• Increase / decrease bobbin tension
• Increase / decrease top tension
• Increase / decrease check spring stroke
• Increase / decrease check spring pressure
• Increase / decrease needle sizes
• Increase / decrease presser foot pressure
• Changed thread, lubed/non lubed, bonded/non bonded, nylon/polyester, thread brands
• Increase / decrease tension on bobbin winder
• Checked thread path
• Checked for inconsistency on how the thread comes off the spool

Currently using 135x17 21 with Tex 70

I mainly sew 1000D DWR + PU Coated Cordura. This problem also occurs when I sew webbing. This machine occurs on multiple of my machines which leads me to believe its a ME problem but I don't know what I'm doing wrong! Its happens on an old Juki 1541 and a new 1341 clone. I notice it more on the 1541 as this is where I do all my top stitching, my solution has been to back off tension, thus making my overall tension not very good but its the only thing that helps. I had this problem when I bought my 1341 clone, the sewing tech looked it over and couldn't find any problem with it. The only alternation he made was to increase the bobbin tension substantially. I always used the drop test method but I'd say the bobbin tension more than doubled which of course made it harder to get good tension. I have asked around from people in the manufacturing industry, the little I've asked, have no idea what this could be.You may ask how I know that its when I begin sewing again. I know this because when I stop with the needle buried, without lifting the presser foot, I make a mark on the fabric next to the foot. I'm at my wits end.

As I the operator is the common denominator I will describe my steps:

1. Wind a bobbin is needed. Thread it through the bobbin tension, then the bobbin then wind it.
2. Place it in the bobbin case as shown in the manual.
3. Thread the machine as shown in the manual.
4. Pull bobbin thread to the top my holding needle thread.
5. Place work under presser foot.
6. Bury needle
7. Hold on to thread tails and begin sewing.
8. Take foot off pedal to stop sewing.
9. Put foot on pedal to start sewing and this is when the error happens.

I thought I'd ask here before ringing another technician to come and have a look at it.

Thank you

Edited September 6, 2023 by Relative
more info

[Gump]

Have you tried it with the needle positioner stopping in the up position? Also try a size 18 needle as it will allow the material to grip the thread more, causing more resistance to stitch pull through.

[kgg]

22 hours ago, Relative said:

I thought I'd ask here before ringing another technician to come and have a look at it.

 

30 minutes ago, Gump said:

ave you tried it with the needle positioner stopping in the up position? Also try a size 18 needle as it will allow the material to grip the thread more, causing more resistance to stitch pull through.

I would just remove the needle positioner all together but that is me. A couple of tests you could try after making sure the top and bobbin tension are correct, bobbin is installed correctly and your thread path from the thread spool is set up proper( a couple of photo's of this maybe helpful):

i) reset the needle positioner to the up position and see what happens

ii) reset the needle positioner to the down position and see what happens

iii) remove the needle positioner by just unplugging it from the box of tricks and see what happens.

For Tex 70 ( V69 ) depending on the thickness of material being sewn I would go with either a #16 or #18 needle. A good reference chart for needle to thread combinations is located at https://www.tolindsewmach.com/thread-chart.html

kgg

[dikman]

Disable the needle positioner and see if it still happens.

[Relative]

On 9/7/2023 at 6:39 PM, Gump said:

Have you tried it with the needle positioner stopping in the up position? Also try a size 18 needle as it will allow the material to grip the thread more, causing more resistance to stitch pull through.

 

22 hours ago, dikman said:

Disable the needle positioner and see if it still happens.

 

22 hours ago, dikman said:

Disable the needle positioner and see if it still happens.

What's with all the needle positioner hate aha

But I think you guys may be on to something. I did a little testing this afternoon and found that if I set the needle position to the up position then this problem doesn't happen. Yet if I leave everything the same and only change it back to the down position, the problem begins again. Any idea of why this is? For the longest I thought it some kind of bobbin backlash. However on the cylinder arm I slid the bed plate so I could watch the bobbin and see what was happening. When I stopped sewing I put a finger on the bobbin and used the tip of a pen to press against the thread to check for any slack. Now I  don't know what the correct amount of slack or lack there of there should be but to my un trained eye there was none.

On 9/7/2023 at 7:11 PM, kgg said:

For Tex 70 ( V69 ) depending on the thickness of material being sewn I would go with either a #16 or #18 needle. A good reference chart for needle to thread combinations is located at https://www.tolindsewmach.com/thread-chart.html

 

On 9/7/2023 at 6:39 PM, Gump said:

Also try a size 18 needle as it will allow the material to grip the thread more, causing more resistance to stitch pull through.

In the past I used a size 18 but always had trouble getting "good" tension. I could never get the knot to sit in the middle, I'd tighten the top tension and eventually the knot would shoot out the top of the fabric with a lot of force. Hence why I switched to a 21 as I find it easier to get a better stitch. I always but it down to the Cordura as I've sewn vinyls before and used a 18 needle without any issues.

Another thing I thought, is it possible that I'm using too heavy duty machines for what I'm actually sewing? For example I noticed that when I layer up to 4 + I can typically get a good tension and not have the bobbin issue occur. I suspect it is still being pulled up but because the stack of fabric is thicker its simply hidden inside. On the 1541 I'm mainly topstitching zippers so 2 layers cordura, 1 zipper, 1 lining and on the 1341 its 3 layers of Cordura and 4ish lining. I just find it very strange that this happens across multiple machines yet I'm the only one to run into this.

I have noticed another potential issue on the 1341 clone where the top thread sometimes gets caught on the wrong side of the hook after going through the hook thread opener and makes a kinda "plunk" sound as the needle goes back up. Will add pics tomorrow.

Thanks guys

[dikman]

Not needle positioner hate (), I have one but don't like it for what I do. I can see where they would be very useful for high speed sewing but my leather machines are all slowed down and I can easily control where the needle stops. The last thing I need is an extra hole where I don't want it.

[kgg]

2 hours ago, Relative said:

But I think you guys may be on to something.

 

2 hours ago, Relative said:

Any idea of why this is?

The problem as I see it, especially thinner items, there can be a few variables at play.

i) if the forward and reverse stitches aren't in perfect syn then you could be dealing with a tension issue in the stitch cycle particularly should you decide to change direction

ii) if the timing is off just a touch then you probably going to have a stitch problem

iii) then you have to deal with how accurate the needle position software is as these units are generic in nature and typically not tuned for one style/type/manufacture of machine. Some of these don't work properly on some machines and work OK on others

iv) how accurately and securely they are mounted to the frame of the machine.

Some people love them, some not so much. I don't particularly even like brushless servo motors as the box of electronics adds another layer of complication when trouble shooting. Then add in a needle positioner and it can become a real problem to back track and correct problems. I guess I fall into the "not so much" group but that is probably just me.

kgg

[Relative]

10 hours ago, kgg said:

ii) if the timing is off just a touch then you probably going to have a stitch problem

Hopefully that should show needle to hook timing.

Sometimes the thread goes on the wrong side of the part circled as shown in the image below. When this happens it makes a "plunk"/click sound because the thread gets tightened and slips off. Is this something to do with the hook thread opener opening too soon?:

[chrisash]

You could try adjusting the top thread tension spring

[kgg]

8 hours ago, Relative said:

Hopefully that should show needle to hook timing.

I think on the 1541 you need to adjust the hook timing and it's position. Here is a couple of video's you may find helpful

https://www.youtube.com/watch?v=cHyn5A1v-hs

https://www.youtube.com/watch?v=5KtJCSfRafA

https://www.youtube.com/watch?v=obvI-v7w0qA

Also here is a copy of the Juki 1541 manuals

kgg

JUKI_DNU-1541-7OwnersManual.pdf JUKI DNU-1541 Parts List.pdf JUKI_DNU-1541-S-7EM01_SERVICE_MANUAL.pdf

[Quade]

I'm not sure if it's just the angle of the picture but the hook looks mighty blunt and even beat up in the top two pics.  If it was my machine, I'd probably replace that hook.  Not that that's necessarily related to your problem.  

Have you tried different bobbin holders on the two machines?  One thing I like about the 1541 style is the easily replaceable bobbin holders. Whereas on the vertical hooks,  the bobbin tension spring is built into the hook. The downside is you can't easily see remaining bobbin thread on the 1541. 

I think the gap between the hook and the needle is too wide on the 1341.   Notice the gap on the 1541.  I almost wonder if the 1541 is too close so it's been hitting the needle and that's why the hook has gotten blunted. 

 

[Gump]

 

In your first pic you show, the thread is the same diameter as the threads of the material, so you can't hide a two thread knot in material only one thread thick. I have had similar problems when sewing Sunbrella fabric with 92 thread. On a single layer the knot would be on one side or the other. A larger needle does help, but on long runs it will tend to shrink your fabric, [lost 1.5" on a 60" run]. Depending on strength requirements, you could use 46 with a size 16 needle and more stitches per inch. I gave up doing boat tops because their not fun and leather still is !