Cobra 4 Issue With Inconsistent Stitches

[monkfinch]

I've read all the Cobra 4 related thread tension posts on this forum and was unable to find one that addresses the specific issue I am having.

First off, I've had my Cobra 4 for about 2 months now and it is a great machine. I had been using it to sew 10 oz. veg tan straps to a waxed canvas hem consisting of three layers of 18 oz canvas w/ nylon 277 thread on top and bottom. Everything is great - consistent, tight stitches.

I started a new project where I am sewing wrapped leather handles using three layers of 5-6 oz chrome tan or stiff latigo (depending on the color way). I set my tension using scrap leather and everything looks good. When I proceed to sew I will get a few dozen stitches in then "pop" - a knot has risen to the surface on that one stitch. I recognize that leather is organic and not consistent in regard to density, but I've done a fair amount of sewing on Singer Class 7's, etc and never encountered this issue.

Sometimes, I will get through stitching the entire handle and everything looks good on top. When I flip it over, I see 1 or 2 stray loose stitches with little curled loops of bobbin thread. Adjusting my tension does not seem to correct this.

I've tried:

1. New needles

2. Adjusting the 2 top tension disks in sync

3. Letting the tension out of the two disks and incrementally tightening them 1/2 turn at a time

3. Adjusting bobbin tension

4. Calling Cobra Steve (He said to try turning the top tension disks 1 complete rotation clockwise)

5. Increasing my presser foot tension (this seemed to help a bit)

6. Sewing glued vs non glued handles

Any help would be greatly appreciated. Thanks!

---Chris

[KAYAK45]

About the only thing left is thread and thread/needle size?

OR, Those elusive shop elves that keep using my knifes and not sharpening them afterword. They also will sand little teeny soft places in your thread spools. Little.. BASTARDS.. I'm going to get one of those ultra night vision camera things, the deer hunters use and photo shop those little buggers out of my basement.

That's what I'm going to do!!!!

GOOD LUCK!

KEVIN

[Northmount]

Are you lifting the presser foot as you make turns or to reposition the leather. Some machines release the top tension if the presser foot is raised very far. I'm not using a Cobra, but my machine has caught me a few times until this action penetrated my thick skull.

CTG

[monkfinch]

Are you lifting the presser foot as you make turns or to reposition the leather. Some machines release the top tension if the presser foot is raised very far. I'm not using a Cobra, but my machine has caught me a few times until this action penetrated my thick skull.

CTG

CTG,

The stitch is a straight run which is why I do not understand why this is happening. I am much better at resolving black and white scenarios (like every stitch is bad), but to have several inches of nice tight stitch then get a stitch with a little loop of loose thread on the bottom...

--Chris

[monkfinch]

About the only thing left is thread and thread/needle size?

OR, Those elusive shop elves that keep using my knifes and not sharpening them afterword. They also will sand little teeny soft places in your thread spools. Little.. BASTARDS.. I'm going to get one of those ultra night vision camera things, the deer hunters use and photo shop those little buggers out of my basement.

That's what I'm going to do!!!!

GOOD LUCK!

KEVIN

Kevin,

I've been using Organ 7x4 - 180/24 with my A&E nylon 277 left twist thread.

I just tried going down to a 160/23 needle and it doubled the amount of bobbin thread loops on the underside of my leather.

---Chris

[monkfinch]

Here is what I am taking about regarding the looping bits of bobbin thread on the underside of the leather.

This example was much worse because I tried a smaller needle and was sewing into preexisting stitch holes from a previous failed attempt.

Generally, I get approximately two smaller loops when I try to sew a straight run on a 15 inch handle.

---Chris

Edited September 10, 2012 by monkfinch

[Northmount]

1347312777[/url]' post='263892']

Here is what I am taking about regarding the looping bits of bobbin thread on the underside of the leather.

This example was much worse because I tried a smaller needle and was sewing into preexisting stitch holes from a previous failed attempt.

Generally, I get approximately two smaller loops when I try to sew a straight run on a 15 inch handle.

---Chris

You need to substantially increase the top tension. With large hole and smaller needle, the knot should have moved higher in the hole, since it wouldn't require as much top tension to place it halfway through. For testing purposes, I like to use black on one side and white thread on the other so I can see where the knot is much more easily. So boost your top tension.

CTG

[Wizcrafts]

Black thread tends to be stiffer than white thread, affecting the position of the knots.

Springy black thread tends to twist around posts, disks and thread guides, throwing off your tension settings.

Smaller needles make smaller holes, increasing the tension needed to pull the knots up.

You can rule your black thread in or out by replacing it with white thread of the same size, on top.

If you find that white thread is better controlled, your alternatives are to use pre-lubricated black thread, and/or to run it through a lube pot filled with silicon or industrial sewing machine oil.

[Trox]

Hi,

I have had this issue before, not with my 441 but with a Adler 105. It was caused by a uneven woven bobbin. Something caught up he thread when I was filling the bobbin, and caused to much tension, making it uneven woven. Check your bobbin for faults. Check your thread rack, is the thread guides directly over your spool (if not it causes uneven top thread tension). Either the top or the bottom thread has uneven tension.

Thats my guess.

Thanks

Trox

[Trox]

If thas not the issue, try a bigger needle.

trox

[monkfinch]

Wizcrafts,

My black thread is noticeably stiffer, but I get the same looping bottom thread with my white thread too. I've been curious about lube pots but suspect they may be messy. Does anyone use one with their 441 or 441 clone? The pre lubricated thread is definitely something to consider.

Trox,

You make an interesting point regarding the threaded bobbin. Admittedly, I've been letting the thread wind on there with little order. I will try winding one in perfect rows and see what happens.

What really puzzles me is I can stitch a piece of leather and get knots on the top as well as loops on the bottom, which does not make a lot of sense to me.

Another observation - I reread the manual that came with my Cobra and there was a section that mentions how the top tension disk is the main tensioner and the lower one is for fine tuning and will determine the "height of the stitch". I had been following other instructions and making simultaneous adjustments to both disks. Today, I am going to try dialing in reasonable tension with the top disk then see if I can bury my knot using separate adjustments to the lower disk. Anyone have experience with this approach?

Thanks for everyone's help so far!

---Chris

[Wizcrafts]

I run all my top thread through the lube pot on top of my machine. I keep liquid silicon in it. The pot came with my machine (Cowboy CB4500) and the silicon lube came from Toledo Industrial. It doesn't mark the leather.

[monkfinch]

I run all my top thread through the lube pot on top of my machine. I keep liquid silicon in it. The pot came with my machine (Cowboy CB4500) and the silicon lube came from Toledo Industrial. It doesn't mark the leather.

I am definitely going to check this out. I have an oil pot for Singer Class 7 in a parts drawer. It may work on my Cobra.

---Chris

[Northmount]

Black thread tends to be stiffer than white thread, affecting the position of the knots.

Springy black thread tends to twist around posts, disks and thread guides, throwing off your tension settings.

Smaller needles make smaller holes, increasing the tension needed to pull the knots up.

You can rule your black thread in or out by replacing it with white thread of the same size, on top.

If you find that white thread is better controlled, your alternatives are to use pre-lubricated black thread, and/or to run it through a lube pot filled with silicon or industrial sewing machine oil.

Nice to note the difference in black and white thread. Thanks.

Smaller needles of course make a smaller hole, however in his test he was sewing through exisiting holes punched by a larger needle. So it is not an accurate test. But it does point out that the top tension was really not adequate.

I sure like pre-lubricated thread. Bob Kovar at Toledo has a good stock, color and size selection.

CTG

[monkfinch]

I pretty sure I solved the problem with my inconsistent stitches.

As some of you may already know, the Cobra Class 4 comes with a bunch of accessories including different plates and presser feet. As I mentioned in a previous post, I had been using my Cobra to sew 10 oz harness straps to a waxed canvas folded seam consisting of three layers of 18 oz duck. To do so I had been using my right toe presser foot with the "blanket set" plate and notched feed dog. This setup "walked" over the canvas and leather nicely. However, my rolled leather handles DO NOT like this setup and the subtle lift of the feed dog seems to be what is causing the nasty bobbin thread loop.

This is why adjusting of the tension disks did not help my issue. It also explains how I could have knots on the top and loops on the bottom at times. That puzzle literally melted my brain.

When I reconfigured my Cobra with the right toe presser foot and slotted plate (for strapped goods), the machine now produces a beautiful lock stitch on my handles. I had never tried this setup prior because I did not favor the idea of disabling the feed dog thinking the more things feeding my workpiece through the machine the better. Shame on me for not spending more time with the accessories to see what they can and cannot do. Live and learn...

---Chris

[leatherkind]

I also had troubles with tension, especially with 315+ thread. The machine came adjusted for #130 and i had to go bigger.

It turned out that the bobbin tension was very sensitive to the thread size.

If it starts giving you a hard time again check the tension by pulling the thread with a luggage scale out of fully threaded machine.

I got best results when both threads top and the bottom were tensioned to approximately 4lb (2000g).

I also noticed that the lesser the tension the harder it is to get the stitch to lock in the right place.

http://leatherworker.net/forum/index.php?showtopic=34194&view=findpost&p=214132