Ugly stitches Cobra Class 26

[CFons]

Hi All, 

I am trying to use the cobra class 26 to make small vegetable tanned leather wallets. But for some reason I can’t get the tension right and the bottom of the wallet looks terrible. Some spots look amazing and others look terrible. My leather is 1.2-3.6 ounces total depending on how many layers are in the wallet. My needle is 18LR and my thread is 138. I know the needle is a little small for this thread size but this was happening even with a larger needle size. I also like the look of the thicker thread. Does anyone have any suggestions on how I can fix this? I’ve adjusted the tension but it didn’t solve the issue. I will add that this doesn’t happen if I use a single layer of a softer 2mm oil tanned leather. I’m starting to wonder if I bought the wrong sewing machine. Is it just too beefy? Or is it just user error?

 

any suggestions would be appreciated!

[AlZilla]

Assuming that you started at the top in your picture and things deteriorated after you turned the corner, how did it look when you got back to 3 layers?

Funny how it looks fine until you turn the corner headed down and then the tension looks unbalanced and gets progressively worse.

[DieselTech]

I'm watching this thread. I am along for the ride. 

I just ordered a new cobra class 26 & I hope I don't have that problem.

I am hoping you figure this out. 

I thought the bare minimum for needle size on 138 thread was a #21 needle. 

I use a #23 needle & 138 thread on my cobra class 4, but got tired of "dummying it down".

[CFons]

Actually I started on the other side first and it goes from looking bad to good and bad to good. The light colored leather has three layers, then two layers on the black and the the lighter black is a single layer and that definitely looks the worst. 

[TomE]

I think your thread is too heavy for the thinnest parts of the project.  Not enough thickness to hide the knots.  I have a Class 26 loaded with #138 thread and a 22 needle that handles a wide range of thicknesses but I don't sew anything below 3-4 oz.  Needle size 22-23 is the typical range for #138 thread. 

I would make up some practice pieces with these same leather thicknesses, switch to a larger needle, rethread the machine, and adjust the tension until you're happy with the results.  Should be able to pull the knots to the top then loosen the top tension until they're where you'd like them.

[kgg]

2 hours ago, CFons said:

I know the needle is a little small for this thread size

The needle is really made for V69.

My thoughts:

When you made the turn in the top left of your photo the stitch changed from good to bad. When you turn 90 degrees you need to move the leather when the needle is just starting on it's upward movement. Also since the needle is undersized there isn't any room to allow turning without the leather grabbing / twisting the thread and being tight in the needle which then probably throws off the thread tension.

The bottom thread knot in the lightest dark color leather if it is 1.2 probably just hasn't got enough thickness to hide the V138 bobbin thread coupled with thread tension going off on the turn.

My suggestions:

Do a test run with the lightest color leather, I'm assuming it is the thinnest and see if V138 works properly in that thickness of leather.

Do a test run with the lightest color leather, I'm assuming it is the thinnest and see if V69 works properly in that thickness of leather.

Use a larger needle, #21 or #22 for V138.

 

kgg

[Northmount]

2 hours ago, CFons said:

I am trying to use the cobra class 26

Moving your post to leather sewing machines.

[Goldshot Ron]

As Tom said, adjust your top tension, and check your threading of the machine.  Practice first on scrap until you are satisfied.  What I will do on a practice piece is to cut carefully with my round knife along the seam to check where the treads are knotted within the leather.  This helps to determine your top thread tension.

[Wizcrafts]

9 hours ago, CFons said:

My needle is 18LR and my thread is 138. I know the needle is a little small for this thread size but this was happening even with a larger needle size. I also like the look of the thicker thread. Does anyone have any suggestions on how I can fix this?

First of all, if you must use #138 on top, use a smaller bobbin thread, like #92. It will be easier to hide the knots with a smaller bottom thread.

Next, ramp up the bobbin tension for s strong but steady pull. Balance the knots with the top tensioner. Stronger tensions may help keep the knots hidden in the same position from the bottom. Just don't ramp it up so far that the leather puckers!

Next reduce the slack in the top thread by moving the check spring disks to the left. There should be a curved slot with a set screw inside it on the outside check disk. Loosen the screw, back off the thumb nut a bit, then rotate the disk to the left. Tighten down everything you loosened. Less slack may help center the knots more reliably.

Set the stitch length to about 6 stitches per inch.

Finally, change to a #21 needle. If you have a choice of points, a diamond point is close to a straight point in the results. A diamond point lets the top thread sit on top of the leather more than an S point or chisel point.

[CFons]

Thank you everyone for the suggestions! There are lots of things to try so fingers crossed with a couple small tweaks to the tension and a different needle or thread will do the trick. 

On 9/15/2024 at 11:57 PM, Wizcrafts said:Next reduce the slack in the top thread by moving the check spring disks to the left. There should be a curved slot with a set screw inside it on the outside check disk. Loosen the screw, back off the thumb nut a bit, then rotate the disk to the left. Tighten down everything you loosened. Less slack may help center the knots more reliably.

I’m very curious about this point. I have no idea what it means but I do feel like uncentered knots in the stitching is happening even when using thicker leather and the right needle/thread size.