Juki 563 Not Enough Tension

[AnthonyG]

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.
 

 

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 May 8, 2018 by AnthonyG

[AnthonyG]

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.

[Uwe]

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.)