Issue With Consistent Stitch On Cobra Class 18. Help!

[Boa]

Hi,

Posted on here a while back but couldn't retrieve my login details so here I am with a new account.

Hoping I can get some expert opinion on what is going wrong with my Cobra Class 18.

Basically we are having tension issues every few seconds while using it. We will be stitching and there will be a small 'thump' from the machine which will result in the tension going slightly off and showing an inconsistent stitch. The stitching is for a product that we are trying to sell and we can have these issues constantly keep being a problem. We've fought with this issue since we got it and after having a technician come and try and address things on two occasions, and helping temporarily, the same issue keeps coming back. The tech that came said it could be the servo motor and would recommend removal as a fix............

I've made a video (apologies for my drab presenting style!) to show the problem: https://www.youtube.com/watch?v=IjTBUKUask4 and would welcome anybody's opinion on what might be going wrong (what I might be doing wrong) and how I can permanently fix it. All I need is a 100% consistent stitch. Nothing fancy.

The video is deliberately non public on YouTube and only accessible via the link in this post. I'm conscious that Cobra is run by good people and I don't want to be detrimental to them, but I still need a solution. I'm not out to adversely impact anyone.

This is super frustrating and is holding us back.

Any help, no matter how small, would be greatly appreciated.

Thanks in advance from the UK.

Grant

[Constabulary]

I once had a similar issue with my vintage Singer 111 and figured it was the thread stand that did not feed the thread properly.

Check if your thread travels the right path and if the thread comes off the cone correctly w/o hanging and causing a higher top thread tension.

You know what I mean?

I guess your machine is quite new, if not check the the tension discs if they are probably worn (but I doubt they are worn).

Or it probably the thread it self is bad. Sometimes cheap thread is not evenly twisted. Try a different brand and look if it works better with your machine.

Just my 2 cents...

Edited May 3, 2014 by Constabulary

[Boa]

Thanks. I hadn't thought about it being the thread.

I doubt that is the issue because the thread I am using is the thread that Cobra supplied with the machine. The thread seems to travel ok from the thread stand. The tech that came put a little bit of oiled paper in the bobbin case which seemed to help for a little while, but I need a permanent fix.

Machine is essentially brand new in terms of the tension discs being worn. I will discount that theory because of the fact that we have had good stitches out of it for a couple of days with the oiled paper in the bobbin case. If it was worn tension discs then that fix would not have worked.

I probably should have mentioned the oiled paper fix to help people understand what is going on!

Thanks for the reply.

[Constabulary]

Does it make the "thump" when you run the machine completely w/o thread (top + bottom)?

I´d try it once with the bobbin and once without the bobbin in place just to see if it makes a difference.

Edited May 3, 2014 by northmount

[dirtclod]

I've been sewing for a lot of years and i don't think i ever heard a machine make a thumping noise like that when sewing. Do you have any ideal whats causeing that ?

One thing you might check is make sure that who ever is sewing isn't hitting the knee lift while their sewing. I have one machine that when i was sewing i would hit the knee lift and not even notice it and it messed the stitching up. I finally figured that out and moved the knee lift a little and i moved my stool over some to make sure i didn't hit the knee lift when sewing.

Nice straps !

[amuckart]

Is it the top thread pulling the bottom thread up, or the bottom thread pulling the top thread down?

If your thread path is Ok, and your tension on the top is working Ok, it might be the bobbin winder or bottom tension. If your bobbin thread isn't wound absolutely consistently you could be having issues where the tension is 'spiking' due to uneven wind.

[ponypome]

have you tried hand cranking it without the motor on to see if it still happening

[Trox]

Thats not a motor problem. Here is several things to check out:

Its most likely the twisting (twink) of the thread that does this. Thread top thread true all guide holes, several times around the top head thread pin. And center the guide above the thread spool to be exact in the middle of the spool. This will take the "twink" out of the thread, that make uneven tension. Otherwise, check the thread tension release pin, that push the tension disk open when you lift the presser foot (check for faults). Increase foot pressure will sometimes help on such errors. Check for burr on hook tip. Wrong size or damage needle.

Good Luck and keep the motor.

Tor

[CowboyBob]

You have some good susgestions here already but,I'd like to add one more,watch the thread as your sewing between the thread stand & machine to see if it ever looks like it tightens ,once in a while a spool is defective & as it comes off the spool esp on the bottom it gets pinched & causes this problem.

[Wizcrafts]

Something might be wrong with the bobbin case or basket, or the bobbins themselves. Make sure that the shuttle mechanism is fully tightened and not able to slip as you sew. Also, after winding your bobbins, cut off the beginning thread stud flush with the bobbin. An exposed stub can catch and cause intermittent tension problems.

Try to watch the bobbin as you sew. See if the thread is twisting as it feeds out of the slot and under the bobbin tension spring. This action would cause sudden changes in bottom tension and cause the knots to appear near the top. If this is happening, troubleshoot the bobbin area and your bobbin thread winding technique.

I usually recommend inserting your wound bobbins so that they feed against the direction of the loading slot, making a sharp turn backwards to the spring. Going the other way sometimes results in changes in tension as you sew.

You might try altering both the top and bottom tensions to see if there is a happier place for both of them to get along and give a consistent knot placement.

Edited May 4, 2014 by Wizcrafts