Cobra 4 Issue With Inconsistent Stitches

[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