Juki 158 Double needle thread

[Dave9111]

>>As an experiment, try using only the left needle and feed the right thread to its guide hole.

I did that and I isolated the problem to the left hook which simply untwists the thread.   I also checked for burrs everywhere. 

However per Constabulary's mention of the thread lubricator, I found a piece of foam, cut it and and pushed it into the holder and lubed it with sewing machine oil and put the threads behind the foam.

I also re-threaded the machine per the video, which is how it was threaded when I got the machine.    I had cleaned the tension mechanism when I took it all apart looking for burrs.   Nothing was found but there was a lot of dirt/gunk in the disks.  

Now the tension system seems to be much smoother than when I first got the machine.    The gunk must have been affecting the tension mechanism. 

Now everything is different.   The left hook is still untwisting the thread.   Yet the machine runs ok now, even at high speed, and the stitches look good.    So I think the only way to get rid of the untwisting is to use the right hand twist thread as was mentioned at the beginning of this message thread.   However it is really nice that I can now run regular left hand twist thread and the machine will function!  :-)   The fact that the thread is untwisted somewhat is not great, but its not very noticeable in the finished stitches.   Still, I think having a right hand twist thread in the left needle would be better.   I have a pound of V138 right hand twist, on its way. 

With the thread lubricator/guide in place, the thread is apparently under better control between the takeup arm and the thread guides at the needle bar.

I wonder how long my "foam" lubricator block will last.  I used a small piece of foam carpet padding as the donor material for the lubricator block.   I think it is polyurethane foam.

I added a pict of the current machine threading  and the results of my latest test run.   The unraveling of the left thread is not obvious in the picture since the takeup arm is up all the ways so the threads are under some tension. 

The test run is about 24 feet of stitching.  About half of it at full speed, which I think is about 2300 spm.   There are some double stitches in there as I was testing the reverse as well.   

Anyway, I am going to consider this problem solved for now.   I'll let you know how the right hand twist thread does when I get it. 

I think the key fix was the lubricator/thread guide, which keeps the threads under better control. 

I'm always amazed at how much a little, seeming insignificant change like this can really make a huge difference on a sewing machine.

Thanks for the help everyone!  

 

Edited September 15, 2021 by Dave9111

[Wizcrafts]

@Dave9111 - You can counteract a particular twist in a spool of thread by wrapping in the opposite direction around a thread post or guide that has 2 or more holes. I do this with twisty thread by feeding it counterclockwise through two holes in a post. You might try that, or go clockwise to see if one or the other improves the thread holding its shape.

[Dave9111]

Thread post.   Interesting idea.   There aren't traditional thread posts on this machine.   They are identical to the ones in video.   The post is horizontal and has one hole in the side of it, then the post becomes tubular and the thread goes through the tube.

Pretty odd.    None of my other machines have that type of post/guide. 

I have one wrap around the post before the thread goes into the tube..

Now I wonder would would happen if I put several wraps around the post?? 

Hmmmmm.......

[Wizcrafts]

If your machine has a spare hole on top you might could buy a post with a few holes and pound it in a bit. Ideally, there should be about an inch between the top and bottom and even better, they would be 90 degrees apart. I have that kind of top post on a few of my machines and they are perfect for counteracting twisty thread, or adding extra tension on top without cranking down the beehive spring, which tends to limit the separation when the feet are lifted.

[Dave9111]

On 9/15/2021 at 9:02 PM, Wizcrafts said:

If your machine has a spare hole on top you might could buy a post with a few holes and pound it in a bit. Ideally, there should be about an inch between the top and bottom and even better, they would be 90 degrees apart. I have that kind of top post on a few of my machines and they are perfect for counteracting twisty thread, or adding extra tension on top without cranking down the beehive spring, which tends to limit the separation when the feet are lifted.

Thanks Wizcrafts.   I'll look into that.    I'll also let you know if the right hand twist thread fixes this issue or not. 

The thread post that Michiel showed might help. 

Edited September 17, 2021 by Dave9111

[Dave9111]

The right hand twist thread arrived yesterday.  

Its a V138 bonded polyester that looks nearly identical to the Dabond polyester that I have been using.

I did nothing to the machine other than remove the existing left needle thread that was a left twist thread (Z twist - standard thread) and I replaced it with the right twist (S Twist) thread.

Wow, what a difference!  

No unraveling at all.  The stitches on the right and left side now look the same.   The left top thread looked a little odd before.  Not a huge issue, but they did look different. 

If you have a dual needle machine and the left needle thread is unraveling, get some right twist thread.   I bought the thread from "The Thread Exchange" in North Carolina.   I think it was $29 plus $10 shipping for a pound.

Trivantage has right twist thread as well, but I don't have an account with them yet. 

Trivantage also has right twist thread in PTFE in V90 and V138.  

Here are the threads slack in the machine after sewing about 15 feet of stitches.   Notice that both thread are wound tight, no unraveling.   Compare this to the picture above with the left hand twist thread in the left needle.