Juki 1541S Inconsistent Tension

[DonInReno]

I’d also check every edge that the thread passes over for grooves or burs.  The only part you apparently physically moved is the needle plate - I’d take it off and look closely at it as well as how the bobbin case interacts with it.

Have you taken off the tension disks to look at their condition?  

Have you grabbed the thread coming out of the tension assembly and pulled out a few feet looking for changes?  

With the bobbin in the machine and fed up through the feed dog pull the lower thread to feel for binding on a number of bobbins.  Cheap bobbins are famous for being inconsistent in almost all dimensions and I recently had to toss out a handful of new ones that would bind in the bobbin case.

I hope you figure it out - it’s always fun solving a mystery!

[R8R]

Nylons are tricky sometimes. You definitely want to use the smallest needle possible, and adjust the needle and bobbin thread tensions in very small increments. Never hurts to back the tension way off, then add it back slowly (both needle and bobbin threads, little by little).

As DonInReno mentioned, cheap bobbins can be problematic, especially when trying to find a fine balance of tensions. Also, too high tension when winding a bobbin can make the thread hang up in spots. Makes for mystery stitches where suddenly the bobbin tension goes wacko for just a few stitches.

Like others said, 69 thread typically calls for 18 needles, maybe 19 if it's tough nylon and you need to punch many layers.

Where you have the thread snaking through the guides, make sure the thread is winding through "clockwise". You have it going one way through the first guide, then the other way through the next. The thread may hang up a bit from this from un-twisting then twisting back. (or maybe not but consistency helps rule out other issues)

 

 

 

 

 

[chrisash]

Is there not another small hook between the needle bar and the needle to hold the thread close to the top of the needle

[dikman]

What type of needle are you using? It's generally recommended that for nylon etc a "standard" round point garment needle is best.

[ultimind]

7 hours ago, DonInReno said:

I’d also check every edge that the thread passes over for grooves or burs.  The only part you apparently physically moved is the needle plate - I’d take it off and look closely at it as well as how the bobbin case interacts with it.

Have you taken off the tension disks to look at their condition?  

Have you grabbed the thread coming out of the tension assembly and pulled out a few feet looking for changes?  

With the bobbin in the machine and fed up through the feed dog pull the lower thread to feel for binding on a number of bobbins.  Cheap bobbins are famous for being inconsistent in almost all dimensions and I recently had to toss out a handful of new ones that would bind in the bobbin case.

I hope you figure it out - it’s always fun solving a mystery!

I've removed and cleaned the tension disks and there are no obvious defects - they are smooth and clean. 

Pulling the thread coming off the tension assembly seems to be fine as well. Every different type of thread feels a bit different. Some bonded nylons come off in a silky smooth fashion (Coats Tex70 Bonded Nylon is smoother than A&E) but the same problems creep up regardless of thread vendor or thread age. I have some old spools of Coats Tex70 bonded nylon from 2008 that are significantly smoother than stuff from November of 2017.  FWIW... Running Tex90 bonded polyester with a size 21 needle has far less issues - still not perfect, but the results are closer to being acceptable. Not sure what this means.

I'm going to attempt to source some Juki OEM bobbins and a OEM bobbin case as well.

 

[ultimind]

7 hours ago, R8R said:

Nylons are tricky sometimes. You definitely want to use the smallest needle possible, and adjust the needle and bobbin thread tensions in very small increments. Never hurts to back the tension way off, then add it back slowly (both needle and bobbin threads, little by little).

As DonInReno mentioned, cheap bobbins can be problematic, especially when trying to find a fine balance of tensions. Also, too high tension when winding a bobbin can make the thread hang up in spots. Makes for mystery stitches where suddenly the bobbin tension goes wacko for just a few stitches.

Like others said, 69 thread typically calls for 18 needles, maybe 19 if it's tough nylon and you need to punch many layers.

Where you have the thread snaking through the guides, make sure the thread is winding through "clockwise". You have it going one way through the first guide, then the other way through the next. The thread may hang up a bit from this from un-twisting then twisting back. (or maybe not but consistency helps rule out other issues)

 

 

 

 

 

I'm going to try some prewound bobbins and see if that helps at all. From what I've seen they're wound at the factory with much more consistent tension.

I will be sure to double check my twist direction as it's going through the thread path - I hadn't thought of twist direction as being critically important. Muscle memory serves to make me do it the same each time but I've not really paid attention to the orientation.

[ultimind]

23 minutes ago, dikman said:

What type of needle are you using? It's generally recommended that for nylon etc a "standard" round point garment needle is best.

Groz Beckert round point. I have been using Size 21 needles for the past year with great success on my 111W and on a shared 1541S at another workshop. I have a feeling that stepping down to 18 or 19 is going to be problematic when stepping over thick assemblies or sewing over zipper tape. I may have to swap needles depending on what operation I'm working on.

[DDahl]

I bought a 1508NH that had a similar uneven stitch problem.  It turned out to be the surface finish on the tension disks.  The quick solution was to use a piece of leather and jeweler's rouge to polish the contact surfaces of the tension disks to a mirror finish.  Problem solved!  These machines are designed for course thread. However the thread that I typically use has different friction characteristics.  This creates a jerking because of the change between static and dynamic friction on the threads.  Polished disks solve the problem.  I find that I have to polish the disks periodically when the stitch quality starts to decline.

Dave

[ultimind]

44 minutes ago, DDahl said:

I bought a 1508NH that had a similar uneven stitch problem.  It turned out to be the surface finish on the tension disks.  The quick solution was to use a piece of leather and jeweler's rouge to polish the contact surfaces of the tension disks to a mirror finish.  Problem solved!  These machines are designed for course thread. However the thread that I typically use has different friction characteristics.  This creates a jerking because of the change between static and dynamic friction on the threads.  Polished disks solve the problem.  I find that I have to polish the disks periodically when the stitch quality starts to decline.

Dave

Dave- I'll have to give this a try. They feel smooth to my touch  but that may not be as smooth as they can possibly be. 

[ultimind]

Quick update - What "seems" to have solved my inconsistent tension issues is winding my bobbins on a different winder. The common variable previously was that all bobbins were wound on the onboard winder on the 1541S. I tried winding them on my 111W's side mounted winder and have had several hours of successful sewing with consistent tension.

 

My 111W side mounted winder does seem to have more tension on the disks than what the 1541S disks are able to apply. I've tried maxing out the 1541S bobbin winding tension spring and it still isn't as tight as my 111W's. Would this cause a significant difference in the quality of the wound bobbin?