Juki 341top thread breaking when backstitching

[twotrees]

Hello all,

I have a Juki 341 that runs like a charm, I'm honestly amazed at how I got anything done in the 'before machine times'.

I'm having one issue though that is proving frustrating so I figured I'd turn it over to the hive-mind of this forum. 

I'm running #69 bonded nylon (needle and bobbin) with a size 18 DP Groz-Beckert needle in max. 7-8 oz of leather (at seam overlaps etc.).  Stitching is a breeze on regular runs but every now and again when I backstitch to begin or end a run of stitching the top thread shreds at the needle. This doesn't occur every time I backstitch but seems to be slightly more common when I'm backstitching over thicker areas. 

I've played around with the tension to point but because it stitches like a dream during regular use I'm reluctant to do too much with it.

So, does anyone have any ideas?

Thanks in advance!

[kgg]

I would:

1. Recheck thread path, how the needle is inserted and it is a leather needle.

2. Move up to a size #19 needle. Sometimes depending on the material / thickness you need a slightly larger needle hole. Also going up one size will add a small amount of strength to the needle to help prevent any slight needle deflection. If you don't have a #19 change the needle the one in the machine may have a burr, be dull or be slightly bent. I find it is better to size the needle up one size.

3. Change out the spool of thread. Depending on the manufacturer particularly cheaper thread it maybe defective or you are down to about 15 percent thread left on the spool. If you are using an 8 oz spool go to the 1 lb size which usually has less problems.

4. Change needle every 8 hours of use and more often when sewing certain materials.

kgg

 

[Gymnast]

In this video I have explained a Little about the "hard point" in the sewing cycle with reference to a modification of the hook used. In the video you can also see exsactly the same happen with a machine there sewing plywood.

https://youtu.be/80WASgbKIX4

When you reverse, and the needle and thread pass Down in the previous holes made, you have left lesser Space in the hole, and therefor the friction to the thread gets higher. This can eventually be so high, that the thread breakes near the hook thread U-turn.

You may go up a size in needle or deside to use a heavier thread. You do use a leather point needle - right?

[twotrees]

2 minutes ago, kgg said:

1. Recheck thread path - this was my first thought, checked several times against the manual and a couple of youtube videos, all correct.

2. Move up to a size #19 needle. I'll try this tonight, I had considered that but didn't want to change how my stitches look.

3. Change out the spool of thread. I think this might do the trick.  The thread I'm running right now isn't exatly top of the line and I have a parcel from The Thread Exchange with better quality thread in just waitingto be used. I'll try this tonight too.

4. Change needle I have a special notepad next to my table to record hours for this very reason!

kgg

Thanks for the tips, much appreciated!

 

 

3 minutes ago, Gymnast said:

You do use a leather point needle - right?

Yep, DP is a triangular shaped tip. 

[kgg]

Another problem area to check is the last thread guide right before the needle. Check and see if there is not a small burr or a groove rubbed into the inside of the hole. Small thread could be affected more then larger diameter thread.

kgg

[twotrees]

Solved!!!  I've spent a day or so figuring this out but eventually discovered my needle bar was set too low.  Raising it by 2.1mm allowed the hook point/blade to pass through the loop of thread rather than catching on the thread and the issues is completely resolved.  

Thanks all for the suggestions, I tried them all out to no avail prior to discovering the needle bar problem.  It's true what they say - experience is what you get just after you needed it.