Setting Cobra Class 4 bobbin tension

[Massive]

OK, so following on the thread "new Cobra Class 4 video" (go there for more tension adjustment talk), I promised to post information on adjusting bobbin tension.  I may post a video, but for now, this is what I got:

I removed the hook and bobbin assembly and left the bobbin in, with the factory 270 thread in it.  You can remove the bobbin and use 3 feet or so of thread, and this may give a more reliable read.  If you leave the bobbin in, you need to be sure when you dangle your weight, that you are not restricting the bobbin from turning which is easy to do because the case is open ended.  

Hold the bobbin in your left hand with the hook pointing to the ceiling, and the thread outward, not facing your palm.  I had a few feet of cord falling down towards the floor.  This is the position where the thread has  the cleanest flow towards the ground.

Do this test over a soft floor, like shag carpet so that should you drop the hook it will not be damaged.  Dropping the hook onto a concrete floor could easily destroy it.

I started attaching weight to the thread/cord, pliers, rings of metal, etc...  Until when I gently jerked the hook up and down, the thread would pay smoothly out, and the weight settled on the floor, it was not free running, it would not have pulled out all the thread, and kept on going, but it was pretty near taking off under the weight of the stuff.  Any more weight and I could not have stopped the thread running.

I brought the various weight items into my house and weighed them.  It came out as 7.7 oz.  I think an 8 ounce weight would be perfect.

So there you have it: Attach 8 ounces, hold as mentioned, jerk the bobbin up and down, and the weight should slip or fall uncontrollably to the floor.  But if you cut back the weight to say 7-7.5 oz, it should not pay out easily.

Obviously if 8 ounces just crashes to the floor, your bobbin tension is too low, and if you can't get it to release at all, it is too high.

Once you have correct bobbin tension, you can set the upper tension low, so you can see the knots on the underside of the material, then raise the upper tension until the knots bury in the middle of two layers of 8, say  Those setting should handle most holster work.

If you have a fresh untouched Cobra, or other sewing machine.  Calibrate it as described to develop your own baseline.  I like to save the test thread, and the weight to keep with my machine accessories so I can calibrate the machine again should it ever be necessary.  I also like to write down the test results, and I like to mark screw position on the bobbin case with a fine Sharpie.   

[outrider]

Do these Cobra machines come from the factory with a sample of sewn leather?  Also, I am having trouble understanding why there seems to be so many problems with bobbin tension on these Cobra's.  I have a Ferdco Pro-2000 which is basically the same machine and I have been sewing with it for over 6 years and I have never had to adjust the bobbin tension on it.  I have used various weight threads and still have never had to touch the lower thread tension (bobbin).  I would hope that these units are tested prior to being shipped to customers.

[Cliff Fendley]

Outrider. My machine came with five layers of 8-9oz leather sewn together. Mine had 207 bobbin thread and 346 on the top.

It did ok with thick leather but when I switched to something real thin like a money belt the small bobbin thread pulled up through the big hole the needle was making.

I switched to a smaller needle and top thread and tightened the bobbin tension.

[Massive]

Do these Cobra machines come from the factory with a sample of sewn leather?  Also, I am having trouble understanding why there seems to be so many problems with bobbin tension on these Cobra's.  I have a Ferdco Pro-2000 which is basically the same machine and I have been sewing with it for over 6 years and I have never had to adjust the bobbin tension on it.  I have used various weight threads and still have never had to touch the lower thread tension (bobbin).  I would hope that these units are tested prior to being shipped to customers.

They don't have a particular problem as far as I know.  I had the same "problems" with my techsew.  That was a second hand machine, and the bobbin case was possibly damaged.  On the other hand, I don't personally buy that bobbin tension is a thing that never needs adjustment.  And when you actually turn over the rocks you hear people are having problems.  Haven't you said your machine ran better with 207 on the bottom?  Even if that is the perfect set-up, it is still an apparent limit, what if a person wanted to run 270 top and bottom...  If I bought a Ferdco, calibrating the lower end tension would be one of the first things I would do.

Most sewing machines are sold on the same basis as the leather ones.  The basic injunction is don't touch the bobbin, except...  If you go into the except area it pays to have the ability to deal with it, and fundamental to that is a way to return to the factory baseline setting.  That is what is in this thread.  Many modern fancy machines have automatic bobbin tension adjustments on them.  I am talking home sewing machines.  But all the principles, and issues are the same.  They have auto adjusts because bobbin adjustments are not completely avoidable.  And probably because people occasionally monkey with the settings.

With  my Cobra, it seems perfectly able to sew 270 top and bottom on all the thicknesses traditionally encountered for holster work: belt and holster  linings, main seams and bullet loops.  Not a huge range really, one should not have to do anything to get that stuff done, and if that is all one ever does, there shouldn't be any problems.  But I will use this thing on all kinds of projects, so I expect to some day have to adjust something.

[Red Cent]

My C4 came with 277 nylon bonding on top and I would guess the same on bottom. Tight top, loose bottom. I was told they work for hours getting the machines adjusted before sending them out.
Well, contrary to the accompanying video I started adjusting. Got the top loose but never the bottom tight. BTW, they do not want you to touch anything when you get your machine. Even though they tell you the presser foot height is set in the middle of the "banana slot" since that fits most people.
Also,BTW, my first computer/motor went whacko and they sent me a new one.

Massive this is my first machine. Would you please get a little more descriptive on the bobbin and hook thing.

[outrider]

Massive...you are correct I run 207 on the bottom and 277 on the top (with a 200 needle).  If I wanted to go with 277 on both top and bottom I would jump up one needle size (to a 230 needle) so that the thread fit into the hole when the stitch was pulled...as far as very thin leather I have also experienced the bottom stitch being pulled through the hole but that is due to the thickness of the leather not the tension...I drop down to a thinner thread...say a 192 or 138 and the pull through problem disappears.  Anyway I was just curious as to why everyone was doing all these adjustmenst when I really never ran into the problem.  Unfortunately, Ferdco is out of business now but they always recommended the bottom thread be one size smaller than the top thread.

[Cliff Fendley]

Outrider, mine is opposite for some reason. If I go to a smaller bobbin thread the pull through is worse. I figured because the smaller thread could pull up through the hole easier.

[David Carrico]

The biggest problem with these machines is what is says on the box, "Made in China".

[Massive]

Massive...you are correct I run 207 on the bottom and 277 on the top (with a 200 needle).  If I wanted to go with 277 on both top and bottom I would jump up one needle size (to a 230 needle) so that the thread fit into the hole when the stitch was pulled...as far as very thin leather I have also experienced the bottom stitch being pulled through the hole but that is due to the thickness of the leather not the tension...I drop down to a thinner thread...say a 192 or 138 and the pull through problem disappears.  Anyway I was just curious as to why everyone was doing all these adjustmenst when I really never ran into the problem.  Unfortunately, Ferdco is out of business now but they always recommended the bottom thread be one size smaller than the top thread.

Good info there, thanks.

What I am describing here is not an adjustment but a calibration, so no mater what happens, drop the hook and bend it out of shape, accident in shipping kids armed with screw drivers... One can get the machine back to the start position.

[Massive]

Massive this is my first machine. Would you please get a little more descriptive on the bobbin and hook thing.

Ok, here is something I just looked at I haven't fully tried it, but it should work, no removal of hooks is required:

Remove the dustcap from the end of the arm, exposing the bobbin.

Pull the thread out so that it hangs directly off the bobbin

Pull the upper thread up and out of the way.

Rotate the wheel so the needle buries to it's deepest point into the machine.  In this position, the bobbin mouth should be facing about 7 o'clock, nearly straight down.

Pull the bobbin thread out a foot at the 7 o'clock angle so that it is exiting the bobbin directly, and hang it over a smooth rod like a screw driver so that the thread can dangle towards the floor but still exits the bobbin in a straight line.  

Secure 8 oz to the end of the string.  

With the screw driver supporting the thread again, tug gently on the weight to see if it will start for the floor.  If the weight pulled the thread out easily before you even tugged on it, then you need more bobbin tension, if it hangs there and won't drop even if more weight is added, then your have too much (which I would expect from your description of the knots on the bottom of your work).

I will have to test this to see if it calibrates with the same weight using this method.

If you need video, I can put something up for you.

[Cliff Fendley]

Massive, I didn't put an 8 oz weight on it but just guessing that's about the tension that is on mine and I think mine is right, the stitches are tight and even and the only time it pulls the bobbin thread up in on the single layer of real thin leather like 4 oz. I'm not sure I could stop that and still have it set to sew thick material as well.

I have no complaint when the machine will sew from two layers of 4 oz up to 5 layers of 8-10 oz. The machine sews from 1/8 thick to 7/8 inch thick with no adjustments so I'm happy.

The biggest complaint I've had is the poor manual that came with the cobra.

I never thought until now but a friend of mine has an actual Juki 440 he got new many years ago. I'll see if he can find the manual for it and see what it says on adjustment.

He also has some sort of clone machine, the Cobra and his other clone are flat out pretty near identical to the Juki.

A while back we were talking about real thick material lifting like the needle was sticking, my friend said the Juki would do the same thing and he runs the thread lube when sewing real thick material.

[Red Cent]

Cliff you can raise or lower the foot by adjusting the bolt from the middleo f the banana, as they call it, slot on the upepr back of th machine.

The other day my leather was sticking to the leather and I thought this cheap dry leather. However, iIdiscovered my chain to the foot pedal was too tight not allowing the foot to come ll the way down by about 1/8". Readjusted and problem went away.

Cliff, the author did not have spell check and he describes the world only how he sees it.

Massive, I contacted my expert (quilter wife) and we went through your original description. Worked. Might need to go a tad tighterbut it givs one some perspective on how the sucker works. I will try the latter test also. Thanks.

[Massive]

Massive, I didn't put an 8 oz weight on it but just guessing that's about the tension that is on mine and I think mine is right, the stitches are tight and even and the only time it pulls the bobbin thread up in on the single layer of real thin leather like 4 oz. I'm not sure I could stop that and still have it set to sew thick material as well.

I could set it for the single level stuff by adjusting bobbin tension on the GB6-180-2.  That said, my Cobra is a few days old and I am not going to risk anything.  The nice thing about other machines for stuff like making sails, is you can buy 3 bobbin cases for a few dollars off ebay, so even if one did screw something up, it would not be a problem, just throw in another bobbin case.  Since I would have calibrated the original case that came with the machine, with the original thread that came with the machine, I can always get back to base settings.  I can also rig different cases for sewing different threads.  So I use 90 for sails, but a lot of z69 for stuff like tents.  I can rig a lower case for these different threads and keep them with loaded bobbins.  But with these leather machines, I guess one can get other cases, but they don't just snap in and out with the bobbin.

A while back we were talking about real thick material lifting like the needle was sticking, my friend said the Juki would do the same thing and he runs the thread lube when sewing real thick material.

A few weeks ago I was trying to get a recipe for lube hoping I could use something from around the house.  I had noticed that on the DVD Bianchi used lube, and I used to use it when making sails with a domestic sewing machine.  My Techsew came with a thread oiler.  I find lube particularly useful when sewing through certain rubber cements.  I asked the guys at Cobra about lube, and got a brisk message back saying it was no longer needed because all bonded threads are pre-lubed.  I was having problems with some light thread in a handbag my mom wanted fixed, and I just took my fingers swept up some machine oil, slicked the needle, and the first few feet of exposed thread.  Problem solved.  All the info I could find on the web about thread oil said is was silicon based, so I have a thread lube can from prehistoric sail making days, and I guess I will use that in my thread oiler.  I really don't like silicon, though. 

[Cliff Fendley]

Funny thing is they might say you don't need it but the thread I got from Leather Machine Company is the worse for fraying and having problems in thick material. Steve even said I must have gotten some bad thread and sent me more but it was the same way.

I ordered thread from Weaver and wow what a difference, after that I only have the lifting problem with very thick and hard dry leather. Since then I've been buying all my thread from Weaver, I don't know who the suppliers are for either but it is certainly different even though the spools look the same.

The saddler I know with the Juki said that it is particular with the thread also. I forget now where he said he gets his thread but I'll ask him again next time I talk to him since I'm going to be needing some.

[Massive]

Yeah, I noticed that about the LM thread also.  One can cut the end cleanly, and then it is frayed before it goes through the needle.  Thread finishes are quite variable.  I use the Tandy poly in white, and the Z threads, they are both hard and glossy.  But I have to say the LM stuff is a nice change and looks a little more period correct. 

Does weaver sell to the average joe? I need some heavy red for holsters, like 270.  I thought Cansew sold it, but not apparently.

[Cliff Fendley]

Back when I started buying from Weaver you had to be a business, not sure if it's still that way or not. I can't remember what information they required to prove you were a business. Probably a federal ID# for the business. I don't know what a person does if they aren't incorporated.

The Weaver thread (especially the colored thread) is much tighter bonded the the LM thread.

[Red Cent]

Thats interesting. The thread was fraying between the seconnd upper machine tension adjust and the needle. I also bought some Tandy nylon bonded. I 'm going to remove the LM 277 and replace it and see what happens.