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I'm trying to sew 2 layers of 1" nylon webbing and am getting the top thread showing on the bottom regardless of how tight I set the top tension; See images attached. The black thread is topside, green thread is bottom side. Both threads are size 69 bonded nylon. In the image of the bottom side I've tightened the top tension a little bit each time, until the final row where I maxed-out the tension. As you can see there is virtually no difference.

I've tried two different needle types with the same results: Organ DP x 17 125/20 and Groz-beckert 110/18 RG.

The organ needle is the largest one I currently have, and should be adequate for the size of thread I'm using. I'm wondering if the type of webbing I'm using requires a specific size or needle point?

Things I've tried with no improvement on the bottom side stitches:

  • Increased top tension all the way
  • Reduced bottom tension to almost nothing
  • Re-timed my machine
  • Removed and cleaned the bobbin case/assembly

I will also add, the tension unit is brand new, but I did take the time to calibrate it so tension engages and disengages properly with the knee lift. Images of the tension assembly attached.

Is there something special about setting up this machine that I've overlooked? Any recommendations on things to try would be greatly appreciated.

A.jpg

B.jpg

TensionA.jpg

TensionB.jpg

TensionC.jpg

Edited by AnthonyG

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Hi Anthony,

I noticed that you:

1. Entered your thread through the first hole of the horizontal tension bar just before the first tension disk from the top of the first hole. I think it should enter from the bottom of the first hole.

2. Did you use your knee lift to get the first thread tensioner disks to open so the thread is sandwiched between the disks of the first tensioner?

3. Do you have thread tension just after the second tensioner at the thread hook? If not the thread was not sandwiched between the disks of the first tensioner.

4. Did you thread through the top vertical tension post on top of the machine, you didn't post a picture?

My two cents worth.

kgg

 

 

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I suspect the tension discs never actually get close enough to pinch/squeeze the thread and provide tension, even when the thread tension release mechanism is in the "engage" position (presser feet down.)

You mentioned that you "calibrated" that thread tension release mechanism. Can you elaborate on that?

The tension discs will be loose and "wiggly" when thread tension is released. They should be firm and tight and actually grabbing the thread when engaged.

Just check if you can easily pull the thread back and forth between the tension discs with your fingers when the tension discs are engaged. If theres is no tension, then your thread tension release mechanism isn't working right.

Edited by Uwe

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Thanks for the tips.

1. I just re-tested the tension with your suggested threading direction. While I found it resulted in a bit more tension, the results remain the same

2. I threaded the machine with the disks open and made sure the thread was seated properly.

3. Yes, I get tension when I pull the thread after the second disk.

4. Yes, the top post is threaded:

 

 

IMG_20180506_205235.jpg

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Does the tension work alright on leather? I know I will sound silly for saying it but the thread looks a lot thicker to me than 69 (40 metric) and more like 138 perhaps. Some of these nylon webbings can be very tight and hard and tension problems are not uncommon with the thicker threads.

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37 minutes ago, Uwe said:

I suspect the tension discs never actually get close enough to pinch/squeeze the thread and provide tension, even when the thread tension release mechanism is in the "engage" position (presser feet down.)

You mentioned that you "calibrated" that thread tension release mechanism. Can you elaborate on that?

The tension discs will be loose and "wiggly" when thread tension is released. They should be firm and tight and actually grabbing the thread when engaged.

Just check if you can easily pull the thread back and forth between the tension discs with your fingers when the tension discs are engaged. If theres is no tension, then your thread tension release mechanism isn't working right.

By calibrate I'm referring to the little pin and plate behind the tension unit that control the release of the tension disks. When I got the new tension assembly I had to bend the plate a bit to ensure the pin was engaged in the lifted position. Pics I took for reference:

 

TensionPin1.jpg

TensionPin2.jpg

13 minutes ago, RockyAussie said:

Does the tension work alright on leather? I know I will sound silly for saying it but the thread looks a lot thicker to me than 69 (40 metric) and more like 138 perhaps. Some of these nylon webbings can be very tight and hard and tension problems are not uncommon with the thicker threads.

The tension works fine on lighter materials.

I'm not working on any leather at the moment, but it appears to be fine on both Canvas and 500D Nylon.

edit: this is the exact thread I am using: http://www.thethreadexchange.com/miva/merchant.mvc?Screen=PROD&Product_Code=BNL069GREO04Ba

 

I apologize if any of my terminology is incorrect. I'm brand new to industrial machines, and learning as I go.

Edited by AnthonyG

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Thanks for the close-up pictures. That looks correct to me. 

That tension unit looks just like one I ordered some time ago. I could never get over that "ball" under the tension discs. It offsets the tension discs from the check spring unit. It seems like a part taken from a two-thread tension unit. I ended up ordering an original Juki tension unit. It's a little more money but well worth it in my mind. Alas, your tension unit does not appear to be the culprit of your tension problems. 

Sometimes apparent top thread tension problems are really due to the top thread snagging somewhere on its path around the hook. This may cause top thread to pulled when it shouldn't, resulting in apparent "lack of tension" symptoms.

Remove the hook cover slide and observe a few hand-turned stitches. If the thread snags or snaps at any point, that may be a problem. Bobbin case opener finger position is sometimes the culprit. The thread may snag on its path around the bobbin case tab that sits inside the throat plate cutout, or it may snag on the bobbin case opener finger if it doesn't get out of the way soon enough.

When adjusting the bobbin case opener finger position, be careful to avoid a bind condition as shown in this video (different machine, same concept):

This is how the thread is supposed to move around the hook (and older video snipped from when I was working on timing belt issues on my my Juki LU-563 clone)

Edited by Uwe

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Edit: Just took a look, and I think you may have solved my problem! The bobbin case opener is adjusted such that it is too far away and not engaging with the bobbin case, leaving it to float freely.

What is happening, is the needle thread is getting caught up around the tab. When I go slowly it's even causing some snapping in the check spring which I did not notice before.

It's late now, so I will follow your video and give this an adjustment tomorrow!

Edited by AnthonyG

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On my juki563 the thread going throught the horizontal tension bar starts going through the lower side of the hole upwards then through the next lower hole upwards and so on.Not threaded top bottom top bottom as by your pic.May make a little more tension.

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Have you tried to reduce the bottom tension or try a heavier upper tension spring?

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On 06/05/2018 at 9:45 PM, Uwe said:

Sometimes apparent top thread tension problems are really due to the top thread snagging somewhere on its path around the hook. This may cause top thread to pulled when it shouldn't, resulting in apparent "lack of tension" symptoms.

Remove the hook cover slide and observe a few hand-turned stitches. If the thread snags or snaps at any point, that may be a problem. Bobbin case opener finger position is sometimes the culprit. The thread may snag on its path around the bobbin case tab that sits inside the throat plate cutout, or it may snag on the bobbin case opener finger if it doesn't get out of the way soon enough.

I followed your advice and adjusted the bobbin case opener. This seems to have solved the problem which is great, but it has also made me aware of something else:

At higher tension settings I noticed the little release hook on the bobbin case is holding on to the needle thread and creating a small snap. I'm referring to the little hook I circled in red. When the needle thread tightens up to make the stitch I'm noticing the thread is getting held up by this little hook until the bobbin spins around far enough to fully release the thread. I don't notice it so much when I'm sewing light material, but at higher tension settings, and slower speeds this produces a fairly audible crunching noise/snapping noise, and also causes the check spring to jerk back and forth. See the two videos I attached.
 

Juki563-HookGib.jpg

 

Edit: I realize it's a bit hard to see since I'm using black thread, but you can hear the check spring bouncing back at 0:10 and 0:23 

The check spring snaps back at the point when the thread is released from that little hook.

 

 

Edited by AnthonyG

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Hmm. It seems like I spoke too soon.

My lastest set of tests were done with the grain of the webbing, where I was able to get a tension setting adjusted properly.

The first set of tests in my original post were done cross-grain to the webbing. I tested some different types of webbing and was able to get tension set no problem. I think it's just the particular type of green webbing I've chosen is very stiff in the one direction.

I'm going to try a larger needle and report back soon.

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To avoid the thread snagging on the hook gib extension finger, you can try to advance the hook timing a little bit (rotate the hook a little bit clockwise and adjust needle bar height if need be.) This has to do with the timing of the thread take-up lever motion and the hook rotation. A millimeter one way or the other can make all the difference. If the hook is rotated a tiny bit further clockwise when the thread take-up lever starts pulling up, the hook gib finger gets out of the way earlier and the thread may no longer snag on it. I often adjust a machine by the book (science) and then make tiny adjustments (art) to reach the buttery smoothness of sewing nirvana. 

Occasionally these snag issues are also sewing speed related. Certain snags at slow motion, hand-turned speeds may disappear at normal sewing speeds due to the thread being tossed about like a lasso rope.

Also, Juki now makes two versions of this hook, one for normal thread (B1830-563-0A0) and one for thick thread (B1830-563-BA0.) One of the differences between the two hooks is that the gib on the version for the thick thread does not have that extension finger. I'm not totally sure what the extension finger is supposed to accomplish, perhaps it keeps the thread from tossing about too much and risk getting picked up by the hook as it comes around again. One work-around option may be to replace just that extended hook gib with the stubby version (or modify the existing gib.)

hook gib finger on Juki 563 hooks.jpg

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