Engineer's Manuals and why you should read them - A tale of a used industrial machine with a happy ending...

[twotrees]

Afternoon all,  I've just spent the better of a day with my machine in pieces and wanted to share with you what I've learned along the way.

In the beginning, I bought a used Juki-341N which had previously been used by another leather worker for about a year or so (IIRC) and previous to that in a factory sewing furnace filters.  According to what I could find out, this is a made in Japan machine at about 15-20 years of age.  The machine ran great, had been well maintained and was clean.  The only problem I'd been experiencing was that every now and again the top thread had a habit of shredding.  I couldn't for the life of me work out the cause; I checked, double checked and triple checked my thread path, I tried a larger needle, I switched out thread between brands, I looked all over the thread path for burrs or scratches to no avail.  Eventually I decided that since I make the vast majority of my items inside out, I could live with having a non-continuous seam, I would just restart the seam if the thread broke and carry on - the overall strength of the seam would be unaffected and nobody sees it anyway.

Until yesterday afternoon, when my machine came to a clunking halt.  I had a jam-up, I couldn't hand wheel the machine through more than about 180 degrees of rotation, something was binding it up and my work screeched to a stop with about 8 inches of sewing left to do (ARGH!).  I took out the bobbin and bobbin case and quickly found the cause, thread had become entangled around the hook, the needle guard and all sorts of other parts down in the workings of the machine.  I picked out what I could but it became apparent that I wasn't going to be able to clear the tangle without going deeper.  After removing the feed dog, the needle guard, the bobbin carrier (sp? Not sure the proper name of this part), and the hook assembly I finally managed to clear the tangle but now I was left with a bunch of parts that I knew had to go back into EXACTLY the right spots.  AND I still had to find the cause for the tangle that caused the jam.  AND I had to figure out why I was still getting thread breakages.

Enter the engineer's manual.  This gem of a publication, discovered after about 10 seconds of googling goes into so much more detail about tuning and adjusting than the user manual that it's unclear to me why a user manual even exists.  Within about an hour I'd reassembled my machine, checked my measurements and tolerances and got it back to stitching how it was before.

Great!  But stitching how it was before still resulted in thread breakages...back to the engineer's manual I went and this is where I discovered the true value of this reference.  There are, in fact, several versions of the Juki 341N and the engineer's manual specifies measurements and tolerances for all of them.  In the handy trouble shooting section it stated that thread breakage is often a symptom of trouble with needle-to-hook timing.  Turn to the relevant page in the manual and voila - measurements for the needle bar height for each version of the 341N.  It turns out that at some point in this machine's history it had either been equipped with an automatic thread cutter (making it a 341N-7) or someone had hastily checked the measurements in the manual and adjusted the needle bar height incorrectly.  Either way, the needle bar was set 2.1mm too low.  This lead to the hook point/blade catching and severing the needle thread, rather than passing through the loop.  Loosening the needle bar set screw, tapping the needle bar to the correct height and retightening solved the problem completely.  I've just finished up about 3 metres of test stitching and not a single skipped stitch or thread break.

I'm as happy as could be right now, and it's all down to the engineer's manual.  If you're having trouble with your machine, find it, read it and check your machine against it.  You might find that the problem is something you hadn't even though of.

[Gregg From Keystone Sewing]

Unfortunately, not every machine supplier has an engineers manual for their machines, like many Juki machines do.

  

[Constabulary]

RTFM is always a good advice

You can learn a lot from reading manuals - as long as they are good. Sometime is makes even more sense than watching stupid (and often faulty) YT Videos.