Cobra Class 18

[Jacs]

Hello. I recently purchased a cobra class 18. It sewed for a solid minute until it did not.  The tension is off it seems? I’m using 140 needle with a 207 thread, sewing on 5oz leather. I’ve done more tinkering/diagnosing than actual sewing and feeling a bit down and out at the moment. The needle goes down a few time, then the thread begins to come apart then bunch and breaks. 
What’s happening? Help?

[DieselTech]

1 hour ago, Jacs said:

Hello. I recently purchased a cobra class 18. It sewed for a solid minute until it did not.  The tension is off it seems? I’m using 140 needle with a 207 thread, sewing on 5oz leather. I’ve done more tinkering/diagnosing than actual sewing and feeling a bit down and out at the moment. The needle goes down a few time, then the thread begins to come apart then bunch and breaks. 
What’s happening? Help?

Can you take pictures on how you got it threaded. Also a 140 needle sounds small to me for 207 thread. If nothing else I am sure leather machine company will help get you going. I'll have to look, but I think I use a 140 & 160 needle with 138 thread on my cobra class 26.

Edited October 19 by DieselTech

[kgg]

1 hour ago, Jacs said:

I’m using 140 needle with a 207 thread

The 140 (#22) is NOT the correct size for V207 thread. The 140 (#22) needle is good for V92 in thicker material or V138 in thinner. The correct size would be a 180 (#24) needle. When the needle is to small two things happens 1) the hole is to small and 2) both the leather and needle will fray the thread and probably cut /break the thread. Also are you using system 135x16 or 135x17 needles? For leather you need to use system 135x16 and for fabric 135x17.

Here is a link to a needle size to thread size chart: https://www.tolindsewmach.com/thread-chart.html

Also check the thread path from the top thread spool to the the eye of the needle. Please post a couple of photo's as there could be something else amiss.

kgg

Edited October 19 by kgg

[Jacs]

I am using the 136X16 needle system. Okay!! My needle size is off. I’ll order in the 180s. 
Also, I don’t think the needle should be touching the bobbin fork? Hmm. Is this a timing issue? 
I’ve left some footage of the threaded machine + the needle/bobbin issue below.

thanks so much for the feedback!!

[Jacs]

[kgg]

19 minutes ago, Jacs said:

Also, I don’t think the needle should be touching the bobbin fork? Hmm. Is this a timing issue? 
I’ve left some footage of the threaded machine + the needle/bobbin issue below.

You right the needle should not hit the hook. I would suggest either calling the dealer and getting a copy of the engineering manual or looking at the Juki DNU-1541 engineering manual to get some ideas on the hook to needle timing and relationship.

kgg

 

dnu1541.pdf

[Northmount]

13 hours ago, Jacs said:

 

As you have found, videos take a lot of file space, more than the limits here allow.  Put your videos on YouTube or other host and link to them here.  Then you can post videos with adequate time and resolution.

Moved your post to leather sewing machines.

[Gymnast]

I am just confirming the remarks by others.

Something is wrong, when the hook hits the needle like that. Make sure, that you do not use a bended needle. It could also be the presser foot or feed dog that push the needle towards the hook. You should also make sure, that the hole in the presser foot and feed dog got sufficient size to the needle size you use. I think the machine manual should inform you about that.

For my machines I got almost all sizes of needles, so I am able to alter them for different threads and fabrics I sew. The right needle size for V207 thread is above 140, but I have sewn some vinyl with a V207 polyester thread and 140 needle, so it is not like it should be impossible. It do also help to use leather needles for leather. The thread manufacturer will normally provide you with information about the right needle size. This is an example of that:
https://www.amann.com/products/product/serafil/ 

[CdK]

11 hours ago, Gymnast said:

I am just confirming the remarks by others.

Something is wrong, when the hook hits the needle like that. Make sure, that you do not use a bended needle. It could also be the presser foot or feed dog that push the needle towards the hook. You should also make sure, that the hole in the presser foot and feed dog got sufficient size to the needle size you use. I think the machine manual should inform you about that.

For my machines I got almost all sizes of needles, so I am able to alter them for different threads and fabrics I sew. The right needle size for V207 thread is above 140, but I have sewn some vinyl with a V207 polyester thread and 140 needle, so it is not like it should be impossible. It do also help to use leather needles for leather. The thread manufacturer will normally provide you with information about the right needle size. This is an example of that:
https://www.amann.com/products/product/serafil/ 

Good information here. I would add that there appears to be no standardization of needle eye sizes and offset height between needle manufacturers and needle size alone is but a rough guide. The same for thread sizes, different manufacturers and thread types have differences in thickness etc. The old seamstress trick of using a short length of thread and watching how the needle slides on a 45 degree slope is a method I have adopted.

The link above is useful. I happen to use Serafil and their 135 thread is thinner and stiffer than other brands I have. The differences are enough that different needle sizes and tensions are needed to get a good stitch in the same leather.

[Gymnast]

8 hours ago, CdK said:

The old seamstress trick of using a short length of thread and watching how the needle slides on a 45 degree slope is a method I have adopted.

Thanks. I did not know about this trick. But then Google helped me to look it up, and it did not show up that many places. I found it here by Bernina:
https://blog.bernina.com/en/2023/02/sewing-needle-and-thread/

I tried it on some known threads, and I think it will work to discard too small needles. My 207 thread and 140 needle was on the edge. 

But Google directed me to this other similar method as well proposed by Groz-Beckert:
https://youtu.be/4fsQGtMSFEQ?si=2CGPJffRur3sgU8x&t=121

I think this method will accept too small needles.

Edited October 21 by Gymnast

[AlZilla]

9 hours ago, Gymnast said:

Thanks. I did not know about this trick. But then Google helped me to look it up, and it did not show up that many places. I found it here by Bernina:
https://blog.bernina.com/en/2023/02/sewing-needle-and-thread/

I tried it on some known threads, and I think it will work to discard too small needles. My 207 thread and 140 needle was on the edge. 

But Google directed me to this other similar method as well proposed by Groz-Beckert:
https://youtu.be/4fsQGtMSFEQ?si=2CGPJffRur3sgU8x&t=121

I think this method will accept too small needles.

Google should have sent you right back here for the needle/thread trick.

 

[shoepatcher]

On 10/19/2024 at 6:12 PM, Jacs said:

Hello. I recently purchased a cobra class 18. It sewed for a solid minute until it did not.  The tension is off it seems? I’m using 140 needle with a 207 thread, sewing on 5oz leather. I’ve done more tinkering/diagnosing than actual sewing and feeling a bit down and out at the moment. The needle goes down a few time, then the thread begins to come apart then bunch and breaks. 
What’s happening? Help?

too small a needle.  Go to #160 or #180.

glenn