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15000 Top Tension - Compared Embroidery Mode and Sewing Mode

SparkleFever
 

Hello again, 
Please bear with me whilst I'm working through a process of elimination to work out whether my 15000 machine needs attention from a technician or not or if there's something that I can do.
(I'm happy to take it to a technician if there's something wrong with the machine, but I'd like to be certain that it needs attention because it would mean time off to take it 2hr round trip and time off to fetch it back with another 2hr round trip.  I wouldn't use a courier service for this machine.)

My questions are - 
Is the top tension unit controlled by different or independent mechanisms depending on whether it's in sewing mode or embroidery mode?
If no, then why would the tension appear to work fine in sewing mode but have no apparent top tension in embroidery mode?
If yes, then what level of top tension should be expected in embroidery mode when the setting number is raised say to 4, 8 or even 10?

The problem and results of my investigation so far - 
In embroidery mode, lately stitching out designs is troubled and the symptoms indicate classic lack of sufficient top thread tension - stumbling, top looping/skipped stitches closely followed by shredding and/or thread breaks or snarling.  It shows up worse with polyester thread than with rayon, but when the tension setting is increased with the polyester thread, as would be usual for polyester embroidery thread, unfortunately there's no difference.  The problems continue. 
It's the same whether using the either the red dot or yellow dot bobbin case.
It's the same whether using a new embroidery needle or a new top stitch needle.
It's the same whether using a new, size 11/75 needle or a new, size 14/90 needle.

During this checking and investigation I've used the same on board design stitched at 400spm with the same fabric, stabiliser and hoop. 

In sewing mode, as the the top thread tension setting is adjusted up or down, I can hear the slight clicking from the area of the tension unit  as it's changed up and down the scale with the screen slider.  Also once the  tension unit is engaged by lowering the presser foot, when I do the gentle thread pull test, there is a noticeable difference between the settings from 0 - 10 and at the 9-10 settings there is almost no movement of the thread at all.  The top tension unit appears to be working properly in sewing mode.

In embroidery mode there is no noise at all when the top thread tension slider is adjusted up or down.
Also whether the tension unit is disengaged / engaged by the raised / lowered presser foot, when I do a thread pull test, there seems to be no difference at all on the top thread tension.  Likewise, when the presser foot is down, whether the tension is set at 0 -10 and anywhere in between, there's no apparent difference in the tension.  It's as though there's no tension at all.  That's not strictly true - the only tension on the top thread is the small amount exerted on the top thread by the sprung clip at the first thread guide before the main tension unit.  There is no discernible tension on the top thread whether the unit is set at 0 or 10 or not engaged at all.  It's the same whether the machine is threaded with rayon 40s, polyester 40s, 30wt or sew-all threads.  It's the same whether I do the pull test with a Tajima tension gauge like this one or just pulling by hand.  When I went through the same test and omitted that first sprung clip guide, despite the thread passing through the top tension unit, there was absolutely no tension on the thread at all, even when set at 10. 

Thanks for any help.
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SparkleFever

onlinesewing@...
 

To answer your questions:
  • All top tension is controlled by a single stepper motor that varies the amount of pressure applied to the discs in the tension assembly. It is managed by the machine software.
  • How the tension is adjusted varies depending on which mode you are in. In Sewing mode the tension is active as long as the foot is down and you are actively sewing. If you adjust the tension in this mode you will hear a click as the stepper motor changes position in response to the new tension setting. Embroidery mode works differently. In that mode the tension is held completely open whenever the machine is stopped. If you change the tension in this state nothing is actually done to the stepper motor. It simply updates the recorded value for tension. The new tension setting is not applied until the START button is pressed, so you won't hear any clicks. Since you cannot measure thread tension while the machine is doing an embroidery design, you have to stop it first. That opens the tension, so you will never have measured tension and thread will slide through easily.
In a probably-unwise attempt to diagnose the problem blindly from thousands of miles away, I offer these guesses:
  • My top candidate would be thread debris caught between the tension discs. I gave you instructions on how to "floss" that area, but it doesn't always work. My preferred method is to use the smallest needle I can find to gently probe the area. If you shine a very bright light above the machine and peer in through the top of the first thread slot (on the right) you should be able to make out the discs. With the machine off, foot up, or on in LOCK mode the discs will be open. The two discs are like inverted plates on a shaft running through holes in the center of them. It looks something like this: )-(  [Not an emoji, not to scale] Use the needle to probe above and below the shaft. If there is something in there you should be able to hook it and start the extraction process. My record for extracted thread is a piece about half a yard long. It was a color that the owner had not used in weeks. You would think that this type of problem would show up in ALL sewing, but it seems to be more critical in embroidery. That's probably because every time the machine moves the hoop for other than a normal stitch, the tension discs are opened to allow easy thread passage. If there is a blockage this action causes it to move and change, where normal sewing doesn't really do that. There's one other type of blockage that I only saw once: Janome thread comes with the gummed label perforated around the hole for the spindle. When putting a new spool on the machine that perforation causes a small circle of label to push out, stuck on the end of the spindle. There it can easily get picked up by the thread and carried down into the tension where it can physically stick on the tension discs. This can only be seen by removing the top cover, and fixing it requires a complete teardown of the tension mechanism. One occurrence of this was enough to last me a lifetime.
  • Earlier Janome embroidery machines came with a plastic embroidery foot. Over the course of many embroideries the needle could hit the foot, due to a caught thread or hooping mishap. Sometimes the foot would not break, but would sustain a notch or crack on the inside edge of the hole that the thread passes through. This could create strange problems that looked like tension, but only when the carriage was moving in certain directions. Your machine has a metal foot, which is very unlikely to break, but a needle strike on it could still create a burr that would grab the thread. Check it carefully.
  • A broken needle can damage the bobbin case and/or the hook race that it rides on. This can cause issues as you describe, which are not tension related at all. When the needle goes down it drops a loop of thread that is pulled all the way around the bobbin case, grabbing the bobbin thread as it goes. If there are any burrs or rough edges anywhere in the bobbin area the thread will snag. This can cause loops or skipped stitches. Since you are getting identical results with both bobbin cases, I would remove the plate and bobbin case and check the hook race very closely. Magnification and a strong light helps, but you can also pass a piece of easily snagged fabric around the inside of it. Any burrs will quickly show up. If you find that to be the problem you will need to see a technician, but be sure to point it out when you take the machine in. I was frequently appalled by machines brought to me after another dealer "fixed" the problem by simply tightening the bobbin tension.
  • My last shot in the dark is a machine malfunction. The nature of software is such that a single memory cell with 0 instead of 1, or vice-versa, can cause huge problems. These are impossible to diagnose, and are only revealed when reinstalling the latest machine update fixes the problem. Another possibility is that the tension release is sticking, so that it doesn't close completely. It might only show up in embroidery when it is constantly opening and closing as you stitch. This would require a technician to remedy.

SparkleFever
 

Thank you so much for all this information and the explanation of how the tension unit works in embroidery mode and why there wasn't any difference on the pull tests.  It's crystal clear and another possibility eliminated.

I'll check more closely for trapped thread/lint and any burrs tomorrow morning.

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SparkleFever

Mary Galea
 

WOW!! What awesome information. Jim, you are one "super-tech" to explain all this so logically and concisely. You demystify so much about our machines and it's only since I've joined a couple of FB groups and "met" you that I'm feeling far more confident using the machine. I've had my 15000 for almost 4 years and it's honestly only just run in as I've never really known how to use it or the apps, and now that I read your responses like this one that I feel far more confident. 

Thank you SO very much. 

SparkleFever
 

Having done everything I can, the issue is no better.

Oh well, that settled it so this afternoon I'll take the 15,000 to the Janome Service&Repair Centre with a description of the issues and several stitch samples that show the problems.
There is theirritating tension issue which shows up in both sewing and embroidery mode, another issue in sewing mode with unreliable stitch pickup when the needle position is to the right from 7 to 9.  It shows up worse with fine threads and since day 1 inserting and removing needles has been troublesome. It's as though the slot in the needle clamp is a little too snug for the needle to fit into it and it's very tight to get the needle back out 
  Even though it's not due, I'll also have the machine serviced.
(fortunately I've not yet sold the 11,000 and still have the much loved and trusty 9000 which will keep the sewing mojo happy whilst the new machine is away)

Thanks for the help and suggestions.  Hopefully the machine will come back with perfect performance.
Let's hope so, these machines are costly and I expect them to do the job they're supposed to do.
- - -
SparkleFever

SparkleFever
 

Update -  
The Machine is back from the service centre and behaving as it should.

- New replacement standard bobbin case (+ bought a spare which was calibrated for a fine thread that I use for working on fine fabrics )
- Serviced
- Needle bar replaced under warranty 
There was no apparent damage on the original needlebar and nothing apparently untoward with the needle slot or  however the slot was a smidge tight.  The replacement is fine.

Thanks again for the input.
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SparkleFever