Issue With Consistent Stitch On Cobra Class 18. Help!

[Boa]

Hi all,

I was in the workshop today so I did a quick video of the leather we have stitched: http://youtu.be/Je_fnZoqsiw

As the the suggestions we tried different combos of the threads we have. Yes we did see slight variations in the performance of the thread but even the best performing thread still had small inconsistencies. The general trend is still that our softer 'doughy' leathers make a far more consistent stitch compared to the firmer veg tan. All leathers in this test are approximately the same substance. I wasn't expecting the tension to be correct on each different leather, but I just wanted it to be consistent.

As for the threading......I think this is one of the first things we looked at months ago when we first got the machine and we were trying to work out what was going wrong. I'll bring my attention back to it and see if that is being overlooked. We have tried to thread it all different ways to get a different result I do remember.

[Boa]

Forgot to mention that I am reluctant to blame thread or needle since all thread and needles we have been using to this point were supplied with the machine from Cobra. It's Cobra's own stock. I wouldn't have thought they would be supplying suspect consumables.

[Constabulary]

Forgot to mention that I am reluctant to blame thread or needle since all thread and needles we have been using to this point were supplied with the machine from Cobra. It's Cobra's own stock. I wouldn't have thought they would be supplying suspect consumables.

But that does not mean that there can´t be a bad lot of thread or needles. "Cobra" does not procure the machines, threads or needles itself. It is just a brand name they use. Some Cobras may have a different color but most likely all the modern machines such as Cobra, Techsew, Cowboy... you name it... are basically the same and I would assume they come from the same factory in China or somewhere in Asia. No clue where the thread comes from but you can make an educated guess...

Don´t get me wrong - all the above mentioned brands sell for sure good machines and products but that does not mean that there isn`t a bad lot.

Also, Singer did not produce their own needles (at least in Germany). As far as I know Singer needles came from SFN Needles or Rhein Needles in Germany. I personally figured that SCHMETZ needles work much better (same size with same thread) than the odd brand needles I got with my machine (Singer 111G156 - bought it used and restored it). I have thrown them all away (about 50-60 needles) because I don´t wanted to mix them up with my SCHMETZ Needles. For some repairs I´m even using 40 - 70 years old military cotton thread and with the SCHMETZ needles it works perfect but I had issued with original (!!!) Singer needles or odd Chinese needles like "white egret" or so.

BTW - I had needles from white egret and there were different size needles inside the package that mentioned on the label on the outside... so WTF... I no longer buy them. It´s a waste of money in my opinion.

Maybe try some thread from www.abbeyengland.com or from another supplier. I thinks its worth to give it a try.

[Constabulary]

I Just noticed the Video so it seems not to be the thread since you tried different thread already but I would still try different and / or larger size needles.

[Boa]

I Just noticed the Video so it seems not to be the thread since you tried different thread already but I would still try different and / or larger size needles.

Thanks so much for this. Amazingly I had never come across Abbey. They look great and I will order some thread from them next week.

I'm also going to buy some Schmetz needles on your recommendation and hope it works.

If changing the needles and thread doesn't work after all the troubleshooting I've done and technicians I've seen over the last year (It's not for the want of trying) I'm going to see what Cobra can to to rectify the situation because I need a 100% functional machine for the Christmas rush and as it stands I'm being prevented from launching new products.

Thanks again for bring these suppliers to my attention.

[Constabulary]

Abbey is nice - I ordered some webbing samples from them (they did not even charge me shipping for it) and I will place an order soon.

But I can´t say how their thread is and don´t even know the brand.

I personally like the Amann Rasant thread very much and Amanns SERAFIL seems to be great too but never tried it.

The change of needle + thread is just a guess, I of course cannot promise that this will be the solution of your problem.

[Wizcrafts]

For a while, about a year ago, I had a problem with the top thread moving away from the center of the upper tension disks. I ended up using a drastic fix. Normally, you feed the top thread around a triple eyelet part, then into and around the tensioners. Since this wasn't hold that particular thread down all the way, I actually fed it under the steel spring pin on the right side of the tension disks, then up on the right and over. That absolutely cured the top tension problems. I had to back off significantly to compensate for the added tension from that sharp turn.

Maybe this will help the O.P.

Other things to check are scratches on the hook and the area that is beveled behind the point. Also, make sure the hook is very tightly mounted. Any looseness can cause issues. Check for thread remnants under the hook, in the shuttle area, or even underneath.

[Constabulary]

Another idea is that you probably have to adjust a disc in your tension assembly just a tiny bit.

This certain disc sits between the tension spring and the tension discs. This disc has a small bar in the middle.

This little bar has to be adjusted toward the operator - maybe just a tiny tiny bit (a really tiny bit).

I have attached a picture so you know where it sits and how to put together the tension assembly.

For explanation:

There is a tension disc release pin inside your machine which pushes the lever (#223703) against the small pin (#223704) and this small pin pushes against the bar in the middle of the disc (#204271) and releases the tension discs then you lift the presser foot.

If this bar is adjusted too far towards the machine you may have a permanent disc release and so you loose the top thread tension.

To try if this is your problem just remove the disc with the bar + small pin, put spring and nut back on and adjust the top tension (it may need a bit more tension because the disc is missing) Then sew and see what happens. The only thing is that your top thread will not be released then you lift the foot.

If this solves your problem you have to adjust the small bar as mentioned above.

If not put disc + pin back and start again.

Don´t loose the small pin (#223704) which sits inside the tension assembly!

[robertmeco]

Have you called Steve He will be glad to help with your problem

[Northmount]

Constabulary's post reminds me of a related problem. If you lift the presser foot too far when making turns, you lose the top tension.

Tom

[Boa]

Hi all,

It has been a while since I updates this thread. Two months has passed, but I wanted to make sure I fully investigated the needle and thread choices before coming to a conclusion.

So in this time I have used the standard round point Rhein Nadel needles and no-brand 20tkt (#138) thread that came with the machine from Cobra. On top of that, based on the recommendations I found on here, I have tried the following Coats threads (multiple suppliers used to eliminate bad batch):

Gral (lubricated): 20tkt

Nylbond: 20tkt (#138), 30tkt (#92) and 40tkt (#69)

Terko Satin (poly): 40tkt

I have also tried the following Schmetz needle points (each tried in 140 (22), 120 (19) and 100 (16)):

LR (reverse twist point) for decorative seams.

SD1 (small round point with triangle tip) supposed to achieve the most consistent seam appearance.

SERV 7 (LR reverse twist point) designed with a stronger, but thinner shaft in order to increase needle stability and result in greater seam reliability.

So after using every combination of the 5 thread variations against 9 needle weight and point variations I can now say with absolute confidence that the problem with the machine isn't needle or thread. The Coats and Schmetz did help a little. Seams do seem to be a little be more uniform, but we still get the stitches where the tension is out for 2-3 stitches and then back to normal again, just slightly less but not significantly.

So after about 3-4 months of trying to work out the problem with this machine I am still none the wiser really. About £240 worth of visits from machine technicians and about £80 in experimental needles and thread (types I probably won’t use in the future). It’s not the thread, needle, v belt, threading technique or the leather. Have I been unlucky and received a dud machine? It’s never been right, we’ve only ever been able to get by. It’s a constant worry as to whether I’m going to ruin a strap every time we run it. Out straps are about $20-25 a pop just in materials without factoring in time.

I’ve got to get my new strap types released before the Christmas rush. There cannot be any more delays, even if I’ve got to hand crank them. Just can’t have this machine prevent me from launching new products. I’ve had the packaging all sorted for the last 4 months and I’ve had the leather for the last 7 months. This machine has caused nothing but extra cost and delays since we’ve had it. New products are now 3 months behind and counting, and with the business only being 9 months old, this machine has been a major obstacle in our first year of operation.

I’ll give Steve a call this week and see if we can sort the machine out. I can’t say I am too optimistic at this point, I. I’ve found Steve really helpful in the past (nice bloke) and I did call him when we first had the issues with consistency but the initial recommendations didn’t work. Now that I know more about what the problem isn’t, hopefully we can get something sorted.

On another note, could anyone help me understand how to adjust the walking foot pressure on this machine? The manual with the Class 18 is completely useless and does not show the same machine in the diagrams it contains. I am getting quite bad footmarks (feed dog marks aren't a problem) on the veg tan straps we want to produce. We are going over them with the back of teaspoon and that works quite well, but I want to reduce it as much as possible at the machine to save time. Any chance the walking foot pressure could have an impact on the irregular stitch?

Anyway, please see the pics of the manual when compared to the actual machine. “adjust the pressure of the pressure ‘eoot’”

Any help will be much appreciated.

Thanks in advance to all.

[Boa]

It would help if I actually attached them.

Another idea is that you probably have to adjust a disc in your tension assembly just a tiny bit.

This certain disc sits between the tension spring and the tension discs. This disc has a small bar in the middle.

This little bar has to be adjusted toward the operator - maybe just a tiny tiny bit (a really tiny bit).

I have attached a picture so you know where it sits and how to put together the tension assembly.

For explanation:

There is a tension disc release pin inside your machine which pushes the lever (#223703) against the small pin (#223704) and this small pin pushes against the bar in the middle of the disc (#204271) and releases the tension discs then you lift the presser foot.

If this bar is adjusted too far towards the machine you may have a permanent disc release and so you loose the top thread tension.

To try if this is your problem just remove the disc with the bar + small pin, put spring and nut back on and adjust the top tension (it may need a bit more tension because the disc is missing) Then sew and see what happens. The only thing is that your top thread will not be released then you lift the foot.

If this solves your problem you have to adjust the small bar as mentioned above.

If not put disc + pin back and start again.

Don´t loose the small pin (#223704) which sits inside the tension assembly!

Great suggestion. Have not tried it but I would have thought if the pin was the problem then it wouldnt a random problem but rather more of a pattern to the stitch.............