Cobra Class 4 Stitch Question

[Wager]

Hi Leatherworkers!

I've been following the forum for a while, and because of the great info on this site I just purchased a Cobra Class 4. I just picked it up today and couldn't be happier.

To get a little practice under my belt, I did my first few stitches on some scraps. Although I saw Steve do some really nice stitches, I'm unable to figure out how to solve the problem in this picture. My bottom thread doesn't seem to be pulling through far enough. The leather in the picture is 2 pieces of 2/3 oz veg tan.

Any help would be greatly appreciated!

Thanks,

Joe

[gottaknow]

Hey Joe. Either your top tension is too tight, or your bobbin tension is too loose. I usually start loosening before tightening, so loosen your top tension a little at a time until the stitch is balanced. You can also do a little of both. Tighten the bobbin tension a little and loosen the top a little. You'll figure it out in no time. Enjoy your new machine!

Regards, Eric

[pcox]

If thats the bottom you need more top tension. so thats the top forget what I said. Wizcraft & gattaknow

has you on track

Edited December 9, 2012 by pcox

[Wager]

Thanks guys, that's the top. It seems a bit tricky to tighten the bottom tension on the class 4, unless there's something to it I'm not seeing. I'll keep at it, any more tips would be greatly appreciated!

[Wizcrafts]

If the photo is taken from the top of the leather, either the top thread is wrapped incorrectly around something it shouldn't be wrapped around, including itself, or a post, or one of the 2 disk sets, or the bobbin thread has come out from under the bobbin tension spring.

If the photo represents the bottom of the leather, either the top thread has come out of the tension disks, or is not feeding through the take-up lever, or the bobbin thread is too tight, or the needle is too big, or the thread is too big for 6 ounces of leather.

[Wizcrafts]

Thanks guys, that's the top. It seems a bit tricky to tighten the bottom tension on the class 4, unless there's something to it I'm not seeing. I'll keep at it, any more tips would be greatly appreciated!

Yeah, I Grok your pain. There is a little flat blade screw inside a hole in the bobbin case, forward from the tension spring screw. The screw inside that recess locks down the tension screw. Use the small screw driver that came with the machine to loosen the set screw, then adjust the tension screw for more bobbin tension. When you are happy with the back pressure, tighten the set screw to keep the tension screw from backing out.

[Wager]

Thanks Wiz! I'll give all of these tips a shot. Much apprecaited all!

[Andrew Chee]

Just out of curiosity, what size thread do you have in there? Looks pretty heavy. A heavy thread in something as thin as two layers of 2-3 oz is a little more difficult to get the knot in the middle simply cause the knot is so big. If you're sewing something this light, try a lighter thread as well.

Andrew

[Wager]

I'm using 277. I finally got it somewhat dialed. The thicker leather worked best for sure, and I'm pretty convinced it's the size of the thread for the thickness of leathere I'm sewing.

Thanks for the help all!

[Wizcrafts]

You should move down to #138 thread if you want to sew 4 to 6 ounces. #207 would be as large as you could really.sew at that thinness. You should use a #23 needle for #138 thread, or a #24 for #207 thread, top and bottom.

[Wager]

Thanks Wiz! That's great advice. I'm going to get my hands on some 138 and let you all know how it goes.

[Wager]

Hi All, as promissed, photos of some stitching after working on the tenstion. The attached photo is two pieces of Chromexcel, pretty think, probably 3 oz each, 207 thread with #24 needle. The combo worked great! The stitching is nice and clean with no pulled top or bottom stitches.

Now for my next question - as you can see the presser foot left pretty deep marks. Any tips on a remedy for that?

Thanks again!

Joe

[Wizcrafts]

Back off of the top pressure spring! It is way to tight for such soft leather. This is done by turning the hollow threaded screw on top of the machine, over the outside presser foot. It compresses a heavy coli spring inside the head. You can back it off until the marks are subdued, then use the collar nut to keep it in that position until you need to crank it down for harder leather.

If you unscrew it too far it will pop out! Use a magic marker to indicate where the last good threads are, in relation to the screw position.

[Wager]

Thanks Wiz! That seemed to do the trick, although the foot still leaves a bit of a mark, just not as deep.

[Massive]

One thing I find useful with a new machine that presumably has the factory fresh set-up, is to find a way of calibrating bobbin tension. On my big machines, I remove the retaining ring, and pull out the hook and bobbin assembly. I remove the bobbin. I take something like the 270 thread I use for heavy work and grab about 3 feet of it. I clip that thread in place, and hang the bobbin from it. On my machine it will take a bit of yo yoing to get the assembly to slide down to the floor on the thread. Be sure the floor is carpeted, and safe, as the hook is fragile. If you feel the yo yoing is not an accurate measure, find some weight that will take it down. Do this with your 138 thread, at it's good setting. Take some accurate notes and video. Be sure you are using representative thread, the good stuff.

Why? Because if you end up with a cluster up on tension, it really helps to be able to get back to factory, or functional settings. The let down in that department is the bobbin tension that is not easily read off a few set screws (mark their angle with a fine Sharpie line). With upper tension one can see how it is set with dial position and turn out, etc... And one can easily crank it up or down until stitch sorts itself out. But lower tension is harder to alter, and can be difficult to read. Sewing machines rarely come with any indication of where to set it. So getting some really good, repeatable calibration for it, can save your bacon later on. You will develop a feel for the correct tension, and later just be able to pull on a thread and tell whether it is correct. But I can think of few more usefull exercises towards that end, than playing with calibration.

Of course some people may never alter the bobbin tension, and it may be stable for them. But if you have a big machine that came with say 277, and you have already played at getting it to say 69, or chased some tension settings, the initial settings may already be lost. So having a baseline to measure from may be useful.

On presser foot marks, the overall tension can have some modest effect. The higher you run the tension, the more down pressure you need to make that tension happen, and the more the feet will mark. This is another way it pays to be able to calibrate bobbin tension. So you can get to the lowest setting reliably. Once you have the lowest reasonable bobbin setting, then you should have no trouble getting a balanced stitch without excess tensio. When working at these lower settings, make an inch of sewing, then remove, and examine how well buried the knots are, and see whether the top and bottom thread can be pulled out, and if the two layers are well held together. If all is well you may be at the minimum setting, and the foot tension can be adjusted to match.

Edited January 3, 2013 by Massive