Cobra 4 Inconsistent Thread Tension

[Red Cent]

Wiz, please jump in. Or anybody for that matter.

I took your advice and loosened top and bottom tension. Almost no tension other than the nut is touching the spring on both adjustments.

It sews very well and it produces a very good thread line. Bottom thread meets top thread around half way and is very snug. However, as you sew, something is causing intermittent tension on top. I use 277 top, 207 bottom, 25 S needle (25 chisel/diamond points ordered) and have a lube pot with liquid saddle soap with glycerin.

I can sew one side of a 40 inch belt, 8-9 ounce top and a 4-5 ounce liner, and in one or two places, the top thread will be laying in a straight line and the bottom thread showing up and over the top thread.

Some times, when I finish sewing and want to free thread, I grasp the thread this side of the take up arm and pull a few inches loose. Some times it will be smooth with very little tension and then, the next time, the thread will practically cut the finger(s).

Any ideas?

[Wizcrafts]

Try straightening out the top thread path. If you have it wrapped around a top post, change to inline feed through instead.

Make sure that the starting piece of bobbin thread is cut off flush with the side of the bobbin. If a little nib is protruding, it might interfere with the feeding of the bobbin. It is also a good idea to test the bobbin thread after loading it. Pull a couple of feet and make sure it pulls evenly, without sudden lumpiness. Dip the bobbin thread in your lube and see if it helps.

You should be able to pull the top thread through all the guides and tensioners, with the presser feet fully lifted. If the thread gives sudden resistance, find out where it is twisting, or binding. Black thread is the worst offender.

Clean all guides along the top thread path.

[Red Cent]

Read about the black thread. I also read the post about the fellow from Australia. At first I thought EUREKA!, thats the problem. Then I watched the Cobra 4/Al Bane video again and we (Wife and I) had threaded everything properly for the Cobra. I am heading for the workshop and will test out all the possibilities.

".....with the presser feet fully lifted."

Watching the video, I finally "caught" the thing about pulling the thread with the presser lifted. The "duh" moment.

Thanks for responding Wiz. I will report back.

[Cobra Steve]

Hi Red Cent. The #25 needle is too large for the thickness that you are sewing. Drop down to a #24. This should help. Steve

[Red Cent]

Howdy Steve. We just finished cleaning the bobbin area, oiled per video, and rechecked everything. I do have 24s in a spade point. Will try those until I get the "D" needles in.

"Red Cent...try using 277 top thread and 207 bobbin thread with a 200 (#25) needle..this is what was recommended by Ferdco when I bought my machine...I have used this for years and have never had any problems. Even though they have closed their business the ferdco website is still up...go to that site and go into the needle and thread section and copy down the sizing charts they have. The Ferdco Pro-2000 is the same machine as the Cobra Class 4 except for a few differences."

This came from a old leathercraftsman that posts on Cas City Leathershop. However, I will practice sew a couple of long strips with the 24 to see how it goes.

[particle]

I'm no sewing machine expert, but am I reading correctly that you backed off the top and bobbin tensions completely, and only re-tightened the top tension just to the point where it touches the screw? Did you ever go back and add more tension?

[Red Cent]

Not yet. Here is a practice piece from last evening. This was sewn with a 25s needle, not much, if any tension on the thread. That is not a machine problem right of center in the picture.

http://i229.photobuc...zps4607f410.jpg

I have not found the intermittent cause of this. The run was started on the right went to the other end and turned and a couple of inches before stop, something happened. I believe that it has to do with the side mounted tension. The side mounted tension does not really grab the thread. The tension adjustments squeeze discs together to create friction on the thread holder which looks like a pulley. However, I have posted that sometimes when freeing up thread to cut the leather away, the tension is so resistant that I could cut my fingers. Notice the problem starts at the bottom of the picture, left thread run. This happened after about a 20" run, turned the corner, another run and it happened.

http://i229.photobuc...zps44d988d2.jpg

Edited August 15, 2013 by Red Cent

[Wizcrafts]

Red Cent;

Please check the spool of thread for flip-overs, twists, or possibly the thread winding under other windings as it feeds off the spool.. Follow it through the top guide posts. Make sure you feed it through the little loop in front of the top tensioner. BTW: that steel loop should sit as low as possible in relation to the axis of the tension disks. The greater the angle, the better the feeding around the disk axle.

I have experienced too much check spring (the spring wrapped around the bottom disks that you must feed through on the way up to the take-up lever) tension over-riding the top tension, after reducing the top tension setting to very light. There is a nut, or a set screw on the opposite side of the housing for the bottom disk axle. Loosen that nut or set screw and turn the split shaft whichever way reduces the spring pressure, while still allowing it to move up and down, then lock it back down.

Last, open the bobbin case and blow out any thread fragments. Ditto for the shuttle and shuttle race.

[Red Cent]

I believe the problem has been solved. I rethreaded the machine and left out the lube pot. Every time a bad or skipped stitch occurred, we traced to the bottom tension wheel. Then it dawned on us that the wet thread wrapped around twice was probably sticking. Per Steve, I lowered the needle about 1/16th of an inch and changed to a 24. Per Wiz, the lube pot did not create a straight path for the thread to follow and a thorough cleaning of the machine.

I believe the thread path change, the sticking of the wet thread, needle size, and needle height contributed to me finishing the other half of the belt without any problems. I did a number of practice runs and never had a problem.

I want to thank Steve and Wiz for their advice and time taken. I hope that discussions like this one will provide some help to others if they incur the problem(s).

BTW: I believe the Cowboy machine would work with the lube pot. One time around the wheel would not cause bind. I guess the post on the Cowboy is added tension and does away with the double wrap. Am I close in my observation Cowboy Bob?

Edited August 18, 2013 by Red Cent

[Wizcrafts]

You can't beat a straight top thread path and minimum hard turns for smooth sewing!

I started using pre-lubricated thread some months ago and it more or less does away with the need for silicon in the lube pot. However, I still run some other threads through the lube if their bondings aren't up to snuff, or they are too dry. I do run all brands of thread through the lube if the needle is running smoking hot, which happens at about 8 to 10 stitches per second, sewing medium temper leather (production runs).

Once turn around the bottom post is okay, as long as you aren't using it to add much more top tension. One turn also makes it easier to extract the thread when you fully lift the presser feet with the floor pedal. Note, this means that the top tension disks do most of the work on the top thread.