Intermittent tension issue

[Gymnast]

13 hours ago, DonInReno said:

I recently purchased the most idiotic gadget that I swore would never be worthwhile - a spring scale that reads up to 100 grams.    I don’t need one, and if a bobbin drop test can’t be done on a vertical hook machine it’s easy enough to guess and adjust accordingly if the material needs it.

About 30 grams of weight is roughly what a bobbin drop test shows in the machine I normally sew 138 with.    No surprise there - having a spring scale tell me that isn’t helpful...right?

Well....I had three vertical hooks and went to set the same tensions on them and discovered a lot of variation depending on slight differences in direction of pull.   The worst offenders had the roughest finish on the edges of the tension spring.    Tensions can easily double with minor changes in thread angle.   I hadn’t expected that.

Polishing the edges with 1000 grit sandpaper smooths things out considerably.   

Honestly it doesn’t sound fun to polish every tension spring that lands on my healing bench so I’m not going to check unless there is some kind of problem.  Sometimes ignorance is bliss.  

....and I’ve changed opinion of the thing - it’s rarely used, but well worth the $10.   I wouldn’t recommend the scale to anyone else, but I would recommend polishing the edges of the bobbin tension spring if you have any doubts about it.    Use a good screwdriver and don’t loose the screws!

If I were in your situation I’d first try a different high quality thread and make doubly sure there are no burrs or sharp edges anywhere in the upper and lower thread paths - including polishing the bobbin spring.

 

 

In my experience, thread tension variations can be caused by a lot of different issues. And for some machines tensioners you cannot get rid of too much annoying tension variation. I disagree with Doninrino about getting such instruments, and I can get them for about $1.5 each. I have seen the same issue about tension variation due to direction of thread from bobbin case. You save time, if you have got an instrument to help you instead of doing test sewing to get results all the time, when you diagnose the machine. The issue of tension gauges have been discussed some times in this forum. This is one of them:

 

[bj139]

2 hours ago, kgg said:

 

I see you are using a spool thread sock on the 8 oz threads. I would try not using them as they can give inconsistent thread tension and may not be perfect and catch / snag thread. Also I would try and lower the top arm and spool holder down so the thread doesn't have such a steep angle entering the first horizontal guide. I find the best angle is when the thread enters the first horizontal guide almost horizontally.

kgg

 

 

Good observation about the sock.  In the past, I had inconsistent tension problems running the thread out of the plastic bag it ships in.  This would increase top tension and pull the bobbin thread up.  

[hanns]

13 hours ago, RockyAussie said:

Couple of things I would try here is 1st don't put the thread under that last little spring guide thingy as I have found that any little thing like that the can interrupt the flow after the spring tension disks can cause an issue and secondly I would make sure the first knob with the +/- on it is set very loose. Lastly ...make sure that you have the foot pressure down enough to not let the job raise up with the needle coming out as that will also give a very uneven erratic stitch knot location.

Thanks for the suggestions. I will give these a shot. I'm hoping I have some time to play around with it again tonight.

2 hours ago, kgg said:

Some Juki's and clones in the 341 class have a felt pad that is inserted in the horizontal guide just below the take-up lever which I suspect the tech wanted you to insert the sponge into not the vertical guide as shown in your photo.

The Juki 1541 S and 1508, according to the Juki manual, has the thread leave that horizontal guide and go through the next guide on the "Right" side of the screw. This noted in the sufficiently noted in both Juki manuals for the threading diagram. I suspect that you need to thread your machine like a Juki 1508 not the 1541.

I see you are using a spool thread sock on the 8 oz threads. I would try not using them as they can give inconsistent thread tension and may not be perfect and catch / snag thread. Also I would try and lower the top arm and spool holder down so the thread doesn't have such a steep angle entering the first horizontal guide. I find the best angle is when the thread enters the first horizontal guide almost horizontally.

kgg

Ah, I may have misunderstood what he meant. They can be a little hard to describe over the phone. I'll try moving the sponge to the horizontal guide below the takeup lever.

The manual that came with this machine has it threaded on the right as well. I think I was trying it both ways when this photo was taken. It didn't seem to make a difference but I'll do it on the right per the directions going forward.

Funny story about the socks - I bought them specifically because of this issue. I thought maybe the thread was falling off the spool and getting caught. Sadly they didn't help, so probably no point in continuing to use them.

Anyway I will make some adjustments as suggested when I get a chance and report back.

[kgg]

9 minutes ago, hanns said:

Funny story about the socks - I bought them specifically because of this issue.

The 8 oz size thread spools can be a challenge at the best of times. There are many factors at play with thread both in spool and bobbin. Some of the issues are:

1) Poor thread consistency along the length of thread on the spool. Cheap Chinese thread.

2) Spring back more noticeable on the smaller spools where the thread comes off the top of the thread spool looking like a coil spring which can create thread spring back and unraveling of a portion of the spool. Cheap Chinese thread, old thread that has developed a memory and darker colors like black being the worst.

3) Bobbin thread will very quickly develop a coil memory and as the bobbin gets closer to the end of the thread on the bobbin it looks and acts like a coil spring. Cheap Chinese thread, old thread that has developed a memory, darker colors like black being the worst and being left to long a time on the bobbin. Bobbins should be filled to about 80 percent capacity and filled relatively close to the time you need to use them.

4) Bobbins of poor quality both in dimensional and weight quality. Some can be so bad as not fitting properly on the winder causing the bobbin to be filled inconsistently and actually wobble when placed in the bobbin holder. Cheap Chinese.

kgg

[bj139]

Can you duplicate this sewing a stitch per second?  It might alert you to what is catching on the top.

[Wizcrafts]

I haven't read every word in the replies, so my apologies if this was already mentioned. Sometimes, when bobbin thread changes tension as you sew, reversing the direction of the bobbin may smooth out the flow. Standard practice is to insert the bobbin so the thread makes a sharp turn against the direction of the windings. This is to keep the thread in the slot leading to the tension spring and to offset the rotation of the bobbin case that could cause the thread to unwind inside the case. Most bobbin cases either include an anti-backlash spring or can have one dropped in under the bobbin. These springs may be a beehive shape or a 5 point star, or round with raised portions. If your bobbin case has one of those springs, try feeding the bobbin thread inline instead of against the natural direction of flow.

Note: Changing the direction of flow in the bobbin case changes the tension. You will have to readjust the top and bottom tensions one way or the other.

[hanns]

1 hour ago, kgg said:

The 8 oz size thread spools can be a challenge at the best of times. There are many factors at play with thread both in spool and bobbin. Some of the issues are:

1) Poor thread consistency along the length of thread on the spool. Cheap Chinese thread.

2) Spring back more noticeable on the smaller spools where the thread comes off the top of the thread spool looking like a coil spring which can create thread spring back and unraveling of a portion of the spool. Cheap Chinese thread, old thread that has developed a memory and darker colors like black being the worst.

3) Bobbin thread will very quickly develop a coil memory and as the bobbin gets closer to the end of the thread on the bobbin it looks and acts like a coil spring. Cheap Chinese thread, old thread that has developed a memory, darker colors like black being the worst and being left to long a time on the bobbin. Bobbins should be filled to about 80 percent capacity and filled relatively close to the time you need to use them.

4) Bobbins of poor quality both in dimensional and weight quality. Some can be so bad as not fitting properly on the winder causing the bobbin to be filled inconsistently and actually wobble when placed in the bobbin holder. Cheap Chinese.

kgg

I don't think the thread I'm using is cheap? It's Amann and A&E brand from Thread Exchange. Are there brands of bonded nylon thread that are better? This thread is also new (at least to me, could have been sitting in a warehouse, who knows). The issue happens even with a freshly wound bobbin.

[kgg]

 

2 hours ago, hanns said:

I don't think the thread I'm using is cheap?

The thread you are using are a great brands so the thread shouldn't be the problem. As a note in Canada and I am going to assume in the US A&E stopped selling and producing the 8 oz spools about 3 years or so ago. When this happens how much thread is left on the bobbin?

 

18 hours ago, hanns said:

I was actually working with maybe a 50-25% full bobbin most of the time.

You should start out with a 80% full bobbin and work down. Winding to bobbin to only 50% or less may cause inconsistent thread tension within the bobbin and allowing the thread to basically unravel within the bobbin.  Any chance of a photo of the bobbin filled with the amount of thread you normally wind unto it.

3 hours ago, hanns said:

This thread is also new (at least to me, could have been sitting in a warehouse, who knows)

A & E on their 1 lb spools date their thread (upper right corner) on the label affixed to the underside of the spool not sure about the 8oz size.

kgg

[hanns]

I finally got some time to work on the machine tonight. I ended up getting something that looks better. Here's what I tried:

Note: When I say "didn't fix" I mean I didn't notice a difference. It's possible there were a lot of little improvements that added up.

• Switched to 138 thread for these tests. Amann thread top and bottom.
• Switched to a new TRI point needle. Didn't fix.
• Wound up a new bobbin. Didn't fix, but needed to anyway.
• Change thread path to right side of the spring thing below the takeup lever. Didn't fix, but it's the way illustrated in the manual so well enough.
• Lowered the thread spool holders to decrease the break angle to the machine. Didn't fix.
• Removed the spool sock things. Didn't fix.
• Significantly loosened the small/upper tensioner and adjusted the main ones to compensate. I think this might have helped. It had been pretty tight.
• Significantly increased foot pressure. I had backed it almost all the way off previously to avoid leaving prints in the leather, but it's possible that it was so loose the leather was being pulled up with the needle - exacerbated by larger needles. I think this helped.

At this point I could still see variations in where the knot landed in a single layer of leather, but nothing as egregious  as my original pictures. So I moved on to a more realistic scenario - multiple layers. With much thicker material I could bury the knot enough that it's not visible from either side. I still don't think it's perfectly consistent, but it seems better and I can get acceptable results consistent with my initial tests of the machine when I first got it.

Edited May 21, 2021 by hanns

[bj139]

It seems total upper tension was too high and shifting some of the tension to the larger units may have improved things.  The larger units may be smoother and more consistent in operation.