Juki DNU-241H stitch problem

[earlthegoat2]

Got this machine a few months ago used and it sewed great for about a month. Then this started happening. Sews good then starts making loops on the bottom. Like the take up is not taking up all the way. In the beginning I fiddled with the bobbin tension and switched to better quality thread and that solved the problem temporarily. 

Now it is doing this constantly and is essentially unusable. I have tried different needles as well as rethreading. I have the manual and I have followed it. I have tried to increase tension and all that basic stuff. 

[earlthegoat2]

[earlthegoat2]

[earlthegoat2]

Ok, I think I have it figured out.  Im going to give it a good test to make sure yet and I will get back with the results. 

Here is an older thread where there was a similar problem with a similar machine.  In this instance it was a Juki DNU-241 (non-H).  Even though in that thread there were some other things going on with that machine, IMO the problem was never addressed to completion.

 

 

[brmax]

Some of the main issues in that link were thread path as I re-looked at the photos.

In your post here, in this try out segmentwhat have you done differently. 

Also I wonder how much tension is on the top thread. This is always a curious thing. 

 

Good day

Floyd

[earlthegoat2]

Here is a half arsed video I made documenting the problem.  This was a tough one to diagnose because whenever I would get stitch problems I would hit the knee lift and that would end up letting the thread back into the tensioner and thus allowing the problem to occur with at least predictable frequency.  I was stymied for a bit by the fact that I could remove the material and restart the sewing process and the problem would essentially reset.  Tricky.

 

[brmax]

Are you saying you discovered that the thread was not down in between securely in the tension disc “ totally” at start up. As it cannot ride on top even though between sorta. 

I understand, thats for sure will be loose if one rides the knee lift bumper, that happens to us all at sometime.

 

Good day there

Floyd

[kgg]

Is it that the thread can't seat deeply between the to discs or was this a user threading error, knee lift bump? What I see is that by making your change it is only offering a little extra friction in the thread path rather then thread tension and may be ok for one thickness but not another.

What I would check by lifting up on the foot tension lifter or knee lift to release the tension between the two discs and check to see if the disc can be separated easily. If they don't separated easily then back off the tension nut to reduce the tension on the the tensioner spring. If they are easily separated then pull the thread from both sides of the tensioner at the same time and see if the thread now seats between the discs rather then just riding on the cupped edges. If the tread rides out again do the same thing again and adjust the tension on the discs tighter by screwing the thumb nut in.

kgg

[earlthegoat2]

The thread was properly seated in the tensioner and as the sewing commenced it rode up and out of the tensioning discs over time.  I duplicated the problem several times.  Unfortunately the video does not include the audible "click" as the tensioner discs are freed from the thread. 

It is obvious from the example material that the problem manifested as the sewing continued.  I am interested as to why it happened now and not when I first got the machine.  Was the tensioner worn out or damaged?  I don't know.

Edited August 19, 2018 by earlthegoat2

[kgg]

Have you check inside the front cover to see what is releasing the tension on the discs or tried to recreate the problem while videoing the internal workings with the front cover off.

kgg