Thread Bunching Above Needle

[jfhspike]

I'm sewing 4-6 layers of cloth-backed vinyl with a Juki LU-563, V-92 thread, #18 needle, about 6 stitches to the inch. It's mostly going fine, but every 20 inches or so, I get a problem (as shown in the image below): the thread bunches up above the eye of the needle. I suspect that either

(i) the hook is sometimes catching only half the thread, essentially splitting it into two strands; one breaks, the other continues to work as usual, and the broken one is bunching up, or

(ii) something else is causing one strand to break -- perhaps excessive tension or something.

Anyone have thoughts about what might be causing this problem, and how I might address it? I've wondered if part of the problem might be the "stickiness/slipperiness" of the vinyl, perhaps making it fail to hold the thread down enough as the needle's withdrawn to form a proper loop for the hook to grab. If that's the problem, should I try a larger needle? Smaller? Voodoo?

Thanks in advance for any suggestions you might have.

Edited April 3, 2015 by jfhspike

[Docado]

Hello

I would try using a larger size needle. Look at pinned links for needle, thread sizing.

[splitrail]

Check for burrs on your feed-dog plate.

[SARK9]

I would try a 19 or 20 needle, and look closely at the hole in the inner foot. See if the needle has enough clearance as it cycles through a stitch; ditto as it enters the hole in the feed dog. Some of the 563's I have seen have the needle position set up VERY far to the left in relation to the needle plate and feed dog, to the point you have to use a center foot with a somewhat larger hole.

-DC

[jfhspike]

Thanks for the suggestions, everyone. I tried a different needle (no effect), checked for burrs (none), and then noticed that the problem only happened when I was going fast. At "half-clutch" speed, things worked fine for many many inches of stitching. I figured it HAD to be a hook/loop issue. When I looked at the hook closely, it turned out to be about .04 or 0.5" from the needle. You couldn't quite drive a truck through there, but close. I adjusted the hook position to be a good deal closer, and things now seem to be fine. I would have checked sooner, but seeing the hook/needle position is harder on this machine than my old 31-15, so I never really checked closely. D'oh!

[gottaknow]

While sewing with any speed, the needle on verticle hook machines deflects to the left. You can't see this deflection when just turning the machine over by hand. I move the hook close enough to just knick the needle as it passes, having begun the process by first bending the needle guard to the right. Set your hook tight enough to just deflect the needle a bit, then bend the needle guard to the left to push the needle away from the hook point, but leaving it very snug. This will accommodate most materials, needle choices and threads. Have fun!

Regards, Eric