Intermittent tension issue

[Gymnast]

Two years ago we had a debate on thread twisting and tension. If the pre tension for a tensioner becomes two low in relation to the "output" tension, small kinks can formed or the thread can get a different and unstable pass through the tensioner causing tension variations. Perhaps you may be interested in the findings and videos there:

 

[hanns]

23 hours ago, Gymnast said:

Two years ago we had a debate on thread twisting and tension. If the pre tension for a tensioner becomes two low in relation to the "output" tension, small kinks can formed or the thread can get a different and unstable pass through the tensioner causing tension variations. Perhaps you may be interested in the findings and videos there:

 

I wasn't 100% convinced the issue was resolved, so I spent more time today testing and sure enough there it is again. I was thinking about your test here as well as the issues people seem to have with these smaller spools, so decided to test that part in isolation and video it. Thread seems to be getting snagged before it even gets to the tensioners.

 

[kgg]

Yes, looking at the video your thread is being snagged. This is one of the reasons why I do not use the cheap spool tree that seems to come with all new machines these days. I noticed you don't have the vertical guide pin installed between the horizontal guide just above the bobbin winder and the thread spool stand which may contribute to the problem as the thread entry angle is to steep. The vertical pin helps maintain a slight thread tension from the spool. I would suggest:

i) install the vertical thread guide

ii) lower the thread spool holder down to as low as you can so it basically on the top of the table

iii) readjust the top thread guide arm down which will help reduce the angle

iv) check the spool of thread for a manufacturing defect in how the thread was wound onto that spool or a thread defect. It maybe just simpler to replace it with the other spool of thread and see if it occurs on that spool of thread as well.

What I do is try and get the thread to make as straight a horizontal line ( Photo K-3 ) as possible between the horizontal guide which on the 1541S is just above the bobbin winder, the first vertical thread post pin (which your machine doesn't have installed) and the thread guide hole just above the spools. Keeping a straight line means the thread spool is moved to the far right rear corner of the table. The purple thing in my photo (K-3) is a thread guide that just slips over the original vertical pin and is just used as a simple guide for the bobbin thread. The less angles either horizontally or vertically the thread has to make before the horizontal guide (which on the 1541S is just above the bobbin winder) gives a more constant top thread tension.

I don't use the thread spool stands that came with my machines, don't even take them out of the packaging, they all pose more problems then they are worth. I didn't have a good photo of the spool stand on my 1541S so Photo K19 is a thread spool stand on a Kobe 1341 which maintains this straight horizontal thread path.

kgg

[hanns]

16 minutes ago, kgg said:

I noticed you don't have the vertical guide pin installed between the horizontal guide just above the bobbin winder and the thread spool stand

Are you referring to this?

I will see what I can do to decrease the angle from the spool to the machine and see if that helps.

[RockyAussie]

I think a lot of the steps that kgg has done may help but I would also check to see what results you get when you don't have the thread going under that spring thing down below the thread take up lever. I had a lot of problems once sorting out a similar problem on a 441 variant that for some reason had a similar spring guide set up and once I got rid of the spring holder piece it behaved it self way better. Older machines never had these at all and I have to ask if anyone could explain how this contraption could be of any benefit in this location? Threads often take on a memory from the coil they are on and often there is a fair bit of wriggling around as they come through all of these thread paths so to me putting in a flat holding wiper is just asking for problems. Why do they make the tension disks so smooth and curved and decide that after all that to put in a flat holding piece???? If you know why please let me know.

[kgg]

2 hours ago, hanns said:

Are you referring to this?

Yes. That is the correct location for the vertical guide pin. Your main thread has to be threaded through this before going to the horizontal guide that is located just above the bobbin winder. I would recommend you have your top thread come from the top arm of the spool stand for your top thread directly vertical pin.
When threading this vertical pin with your top thread it will cross over the large round dial for adjusting the amount of lift for the pressor foot and walking foot. So that the top thread doesn't touch the top of the dial you thread this pin by going into the bottom hole first and out of the top hole. The hole in the top arm of the spool holder for guiding your top thread ideally will be as close to being horizontally level and create a straight line from the horizontal guide to the top arm guide hole.This may pose a problem with the type of spool holder you are using.

So you can wind a bobbin while happily sewing along you could replace the 2 hole pin with a 4 hole vertical pin or do something similar to my solution or just have your bobbin thread come directly from the top arm guide hole directly into the bobbin thread guide.

 

16 minutes ago, RockyAussie said:

Why do they make the tension disks so smooth and curved and decide that after all that to put in a flat holding piece????

My take on this is that it holds the top thread for a split second acting as a damper so the thread doesn't go slack or to tight in the cycling of the top thread arm and reduce unwanted thread movement at the needle. Some other machines don't use this at all while others particularly in the 341 class use a felt pad inserted in the guide just below the take up level to achieve the dampening effect. The spring loaded flat piece system is also used with some 2 needle systems to help keep the two threads separated during the sewing cycle with one thread being on each side of the screw. I have used my 1541S both with and without the flat wiper. I found not much if any benefit when using V69 or V92 but a difference with black V138.

Just my two cents worth

kgg

[Gymnast]

13 hours ago, hanns said:

I wasn't 100% convinced the issue was resolved, so I spent more time today testing and sure enough there it is again. I was thinking about your test here as well as the issues people seem to have with these smaller spools, so decided to test that part in isolation and video it. Thread seems to be getting snagged before it even gets to the tensioners.

 

If you look at the linked video about thread twisting, you will find, that it is important how you make the pass of the thread through the steel plate with holes in it. You go clockwise in forward direction. I would chose to go anticlockwise to reverse the twisting from this steel plate.

[hanns]

9 hours ago, RockyAussie said:

check to see what results you get when you don't have the thread going under that spring thing down below the thread take up lever.

I forgot to mention: I did try this. I just removed the screw and the little spring arm assembly to get them out of the way so the thread could go through the guide freely. It didn't make any difference in this case, so I put it back on.

Edited May 23, 2021 by hanns

[Wizcrafts]

You need to wrap the thread counter-clockwise around something to counteract the twist of the wound spool. It could be a post that has holes on the top and bottom, or the guide before the pre-tensioner.

[LindanHotAir]

In one of the photos it looked like the thread was going through both tensioners. Normally 2 tensioners on a single needle machine allow the operator to set them up for 2 different threads. Thread through the pretensioner which is normally used to control the cutting length, and normally starts out with the knob flush with the end of the screw. Then use one tension assembly, then thread the check spring assembly. The check spring should operate to prevent the thread from going slack between the tension and the take up lever.