Why is my needle feed machine eating the work?

[williaty]

Video of the problem:

 

https://www.youtube.com/watch?v=b_Arp_nIQhE

 

 

The problem child is a Juki DLN-5410N-7-WB I rescued from a factory. All of the automated functions don't work because I wasn't able to salvage the brain box. Many parts had been stripped from the machine and I've replaced them. It may be relevant that the presser foot, needle plate (throat plate), and feed dogs were replaced with parts from Cutex listed as the "normal" options for this machine. The needle bar height was reset since it was way off and the timing was corrected according to the Juki manual. The feed timing between the feed dog and the needle appears to be correct as they move in lockstep. The feed differential between the feed dog and needle feed appears to be neutral as they move in lockstep. The fore-aft position of the feed dog has been adjusted to get the needle landing dead center fore/aft in the hole in the feed dog but the needle is offset to the left within the hole. The machine stitches perfectly well at all speeds and stitch lengths.

The problem is that the machine will intermittently stop letting the fabric flow out from under the feed dog and start wadding up it. It actually wads it hard enough to permanently crease the fabric and, in one case, actually tore the fabric. It *seems* to happen a lot more often with very limp/soft fabric and doesn't happen often or at all with stiff/heavy fabric. On a test sample, once I had a bunch of lines of stitching in the fabric which resulted in adding some body to the sample, it stopped catching. In this demo video, I deliberately fed the machine a lump of fabric to trigger this problem so you all could see it but it'll happen eventually if you sew flat, smooth fabric long enough. It appears to be catching on the back of the opening in the throat plate that allows the feed dogs to come through but I can't be sure because I (obviously) can't see through the feed dog and fabric. Adjusting the presser foot pressure through the whole range of adjustment has no effect on this problem. Pulling the fabric straight up behind the foot while sewing *does* appear to prevent this from happening entirely but this is obviously not a real-world solution.

Any idea what's going wrong or how to fix it?

[DrmCa]

2 things:

1. Check everything for burrs: the foot, the throat plate, the feed dog.

2. Try to reproduce that by stitching clear plastic bags.

And post close-up pictures of the above parts.

[williaty]

EDIT: On Reddit, a bunch of people asked about feed timing and I looked up how to check it, which just raised more questions. Feed timing is referenced to feed dog height so the first thing I had to do was set the feed dog height. When I installed the new feed dogs, I just visually set them so the bottom of the gullies between the teeth came up to flush with the top of the feed plate. Turns out this is way lower than Juki wants them set. I raised the feed dog height at top dead center to the 0.8mm spec Juki calls for. I then leveled the feed dog front to back so that the whole thing was at 0.8mm at the highest part of the cycle. Feed timing is checked by the top of the feed dog teeth rising flush to the needle plate at the same instant the tip of the needle is flush to the top of the needle plate. Turns out that, if you level the feed dog at the top of its travel it's slanty AF at this point in its travel. So the feed timing is correct when the *back* of the feed dog is flush to the surface of the needle plate. If I bring the center of the feed dog flush to the needle plate, the needle itself is already ~2mm into below the surface. Obviously, that's even worse if I bring the front flush. So I now have two new questions:

1) When during the cycle is the feed dog supposed to be parallel to the surface of the needle plate (when below the plate, flush to the plate, at maximum height)?

2) If the answer to #1 means that the feed dog is sloping as it comes up through the needle plate, where along the feed dog do I reference for the feed timing?

Additional fact, it does **NOT** do this in reverse. It'll eat lumps and spit them out just fine in reverse. The only difference I see is that the toe of the presser foot isn't applying any pressure at all anywhere near the end of the feed dog slot in the needle plate whereas in forwards travel the heel of the presser foot does apply pressure very close to the end of that slot.

The slot has very sharp edges. I wouldn't say they have a burr as there's no snagging feeling if you run your finger over it, just that they were absolutely not softened at all during manufacturing.

4 hours ago, DrmCa said:

2 things:

1. Check everything for burrs: the foot, the throat plate, the feed dog.

2. Try to reproduce that by stitching clear plastic bags.

And post close-up pictures of the above parts.

1) Everything is definitely burr free. I do have concerns about how sharp the edge on the slot in the needle plate is, but it's sharp, not a burr..

2) What weight of plastic bag? Like a mylar O2 seal bag definitely isn't going to wad up. I super cheap store-brand ziplock sandwich bag might. Crappy grocery bag might just cease to be!

[Constabulary]

Maybe try a Teflon foot or roller foot (both dirt cheap).

You seem to sew the material "unguided" (no hands on the material) have you tried "spreading the light fabric with thumb and fingers a little bit?

Edited February 24, 2022 by Constabulary

[KAnderson]

It sure looks like something is snagging the threads in the fabric weave. Puckering is seen coming in from the sides of the fabric as well as bunching up at the outfeed. Perhaps the needle type is not compatible with this fabric, and it is pushing the weave down to where it is getting caught. When I watched the video the first time, I thought thread tension, but after watching several times, it is obvious that the machine isn’t even threaded.

Edited February 24, 2022 by KAnderson
Watched the video a few more times - revised my opinion

[DrmCa]

11 hours ago, williaty said:

What weight of plastic bag?

I am sympathetic but do I really have to babysit you like that? Try different things, see what happens as you watch it through transparent plastic. If it only happens to woven/knit fabrics then consider KAnderson's theory.

[CowboyBob]

The back of the foot is pushing your material into the top edge of the needle plate,you might try to loosen the foot pressure ,the best cure would be to grind off the sharpness at the top of each feed dog slot at the top edge of the needle plate like the pic shows.I know your plate has probably 3 slots so gring or file each slot & let us know how it works.

[DrmCa]

It pains me to think of whatever happened to the machine that the above plate had come off. I hope the operator did not lose an eye.

[CowboyBob]

53 minutes ago, DrmCa said:

It pains me to think of whatever happened to the machine that the above plate had come off. I hope the operator did not lose an eye.

I was testing a machine once & a needle broke,hit me in the cheek it felt like a bee sting,lucky for me no bleeding wound BUT I sure am glad to have to wear glasses.I I'd hate to think what could happen if it hit my eye.So note to all WEAR SAFETY GLASSES when sewing esp when using bigger needles & heavier leather.

[Wizcrafts]

3 hours ago, CowboyBob said:

I was testing a machine once & a needle broke,hit me in the cheek it felt like a bee sting,lucky for me no bleeding wound BUT I sure am glad to have to wear glasses.I I'd hate to think what could happen if it hit my eye.So note to all WEAR SAFETY GLASSES when sewing esp when using bigger needles & heavier leather.

Back in November my partner in the shop made a holster and handed to me to sew. He failed to mark the STOP point and I hit a steel clip he embedded between the layers. The #25 disintegrated into dozens of pieces of shrapnel, most of which hit me in the chest and some in the face. My glasses protected my eyes.