Issue With Consistent Stitch On Cobra Class 18. Help!

[Constabulary]

Never heard of such issue before but I learn something new every day. Glad this is solved.

[Boa]

Hi all, sorry about the time taken to get back to you on how this all worked out.

We thought we had it solved but alas it seems we don't. This machine is a total headache.

It all worked well to begin with............

After ordering the new v belt and deciding that was more than likely the sole problem I received after a week or two it and it didn't fit! I was so impatient to get the thing working however I took off the problem belt I got with the machine from Cobra and went to work shaving the problem area down with a super sharp knife, only taking off a dusting of fibres with each moment. I tried it on and off the machine until I was happy there was no change in resistance or thumping as the machine was brought right up to speed. The machine and servo ran without a hitch. We put our 3mm (0.12 inch, sorry I'm a metric kid!) substance leather in and it sewed without a problem and with immaculate, consistent stitching for the whole 20 straps we had to produce. We were delighted.

The problem came last week. The curse of the inconsistent stitch reared it's ugly head again. We are trying to product a new type of guitar strap using a really nice quality full grain Italian leather. We had the prototype all set of the final process of stitching and yet again we got the same random stitching where about 15-20% of stitches either had the top or bottom thread pulled out of the opposite side of the strap. Stitch length is fine and normal but this nightmare with the tension never being consistent persists.

The difference between the Italian and the first (American, most of you will be pleased to know) leathers is the consistency. The American hide is a softer 'doughy' waxy drag leather and the Italian is a firmer veg tan. The Italian is a perfectly normal veg tan, nothing out of the ordinary. American: http://www.aacrack.co.uk/catalogue.asp?product_id=50 and the Italian: http://www.aacrack.co.uk/catalogue.asp?product_id=87 I thought I would link the leathers just to help in case anyone in the UK is looking for leather suppliers (they ship worldwide too). AA Crack are fantastic. Good people with a good warehouse which I have personally visited. You can order single hides or in the 1000's of sqft. Highly recommended...................Anyway.........that's off topic. The leathers have similar substance and are well within the range for the Class 18 but it is just messing up on the veg tan and I have no idea why.

I'm happy that the servo issue and 'thump' is fixed now. A faulty v-belt was the culprit and I'm past that. Unfortunately I now have no idea why we are still having issues. The sad thing is we got this machine solely to start a business and we've had a really good response from our product so far and we are really encouraged, but until I get this problem sorted we can't put out second strap type out. We could have bought a cheaper machine here in the UK but went with Cobra on their reputation for more money and 6-8 weeks longer shipping because we are trying to produce the best work we can and we are making a high end product. I'm just pulling my hair out now. It costs us £15+ in materials every time we have a stitching malfunction on a strap. I want to product a Horween strap but frankly at the cost of that leather I'd be terrified to attempt it on this machine. Thoroughly fed up. Sorry to sound so negative, but it is the one sticking point in an otherwise amazingly enjoyable start up business.

Any suggestions? You all got to the bottom of the problem with the v-belt, so I am hoping we can solve this one too.

[Constabulary]

I´d probably try a different thread brand and maybe a thicker needle. What needle brand are you using? SCHMETZ is highly recommended.

Do you pull the thread over the little hook in the tension assembly? If not - make sure you do it!

Have you tried to give the thread take up spring a bit more tension?

[Northmount]

Did you make any changes to thread (including colour) between the successful run and the new run? Was the machine re-threaded? Part of you trouble shooting procedure should be to look at all the changes that occurred between the 2 runs, not just that the leather was changed.

"15-20% of stitches either had the top or bottom thread pulled out of the opposite side of the strap." This tends to say that both the top and bottom tensions need to be increased. And as the previous post mentioned, needle size affects the tension behaviour too.

Tom

[catskin]

My guess is that you are missing one place in the threading either going the wrong direction through something or missing something that it needs to go over through or around since you seem to never have had it working consistantly well since you got it. The reason I am making this suggestion is I was threading one of my machines wrong for years and it was doing much the same thing. It would some times sew perfectly for miles and then do what yours is doing and then seemingly fix it self. I had no threading diagram. So check the threading as though you are threading it for the first time ever.

[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.