Cobra Class 4 Question

[SethJ]

Ok, so I did talk to Steve yesterday and he answered all of my questions concerning the cobra class 4 machine ,...but I forgot to ask him this one...Why won't the machine sew anything lighter than 6oz? So am I to understand it will sew together 2 thicknesses of 3oz totaling 6oZ? I don't exactly understand why the machine wouldn't handle lighter leathers?

[Wizcrafts]

Technically speaking, your Class 4 will sew under 6 ounces, but only with very light thread, a small needle and tensions rolled almost all the way off. I actually sewed a burlap bag closed on a Cobra Class 4. I also used it to sew zippers onto vinyl jackets, some of which were 4 or 5 ounces thickness. The machine needed a lot of adjustment to do this and this takes time.

Here is a checklist to use for sewing under 6 ounces of material.

1. #69 bonded nylon or polyester thread, on top and bobbin.
   
2. #18 needles (not usually available with a leather point in this size).
   
3. Back off the top tension entirely.
   
4. Reduce the tension on the check spring for the lightest pull that still moves it all the way up and down during the take-up cycle.
   
5. You may or may not need to unscrew the bottom tension spring to reduce top tension.
   
6. Adjust the bobbin tension spring down for a modicum of pull; smooth, but not tight. Don't let the screw head extend so far that the top thread gets caught on it as it feeds around the bobbin case
   
7. Back off the pressure on the feet using the big threaded adjuster on top. You won't need as much force to hold the leather down. Some people do the opposite and crank up the pressure. This just pushes soft leather deeper into the feed dog hole and slot.
   
8. Make sure that the presser foot go all the way down, to secure the leather between stitches
   
9. If you got the blanket foot set with your machine, it may work better than the harness feet. The blanket feet are large and have teeth. The outer blanket foot also has steel all the way across the back, giving more holding power behind the needle and inner foot. This gets around the issue of soft leather lifting with the needle when using harness feet, which are wide open on the back.
   
10. The blanket foot set includes a different feed dog, which has teeth. It may or may not prove more efficient than the smooth dog. Also, the blanket feed dogs tend to have a smaller needle hole than the smooth dogs have.
    
11. Hold the threads back and test on some scraps of the same thickness, adjusting the top or bobbin tension springs to balance the knots.
    
12. If the blanket foot is too wide, take it to a grinder and cut down the right (and/or left) toe
    

[Fat Dog Leather]

Wiz help please!

Sewing on my cobra 4 up to recently with perfect tension on 6oz material. Today it is out of wack with the knot sitting too close to the top. Adjusting the tension springs I have put it out of adjustment apparently not moving both spring at the same rate. How can I get it back into sync?

Would greatly appreciate your advice.

Fdl.

[Wizcrafts]

Wiz help please!

Sewing on my cobra 4 up to recently with perfect tension on 6oz material. Today it is out of wack with the knot sitting too close to the top. Adjusting the tension springs I have put it out of adjustment apparently not moving both spring at the same rate. How can I get it back into sync?

Would greatly appreciate your advice.

Fdl.

Some beginners are known to mark the adjuster nuts on the two upper tensions with white paint. One can even put a white dot on one side of the bobbin tensioner screw. Then, count half turns as you make delicate adjustments.

This assumes that you are starting from a good reference point. Apparently, you have lost that happy place. Let's try to regain the upper hand...

If you have not changed the bobbin tension, nor the bobbin thread, nor inverted the bobbin itself, adjust the top tension as follows:

1. Examine the bobbin thread to see if it has slipped out from under the bobbin tension spring, causing a total loss of bottom tension.
   
2. Check top thread path for twist-overs or knots. These cause unexpected increases in top tension.
   
3. If there is no thread binding problem, if the knots are near the top, loosen the top tension adjuster counterclockwise, a turn at a time, until they drop into the leather.
   
4. If the knots are at the bottom, turn top adjuster clockwise to increase top tension until they are balanced in the leather.
   
5. If the top adjuster nut doesn't bring the knots to the best position, check the tension of the lower adjuster spring and its connected check spring. The check spring is factory set for heavy action, as needed to control thick thread. It may totally override the tension disk settings unless you loosen its lock nut and turn the split threaded post counter-clockwise, to relieve some spring tension. Leave enough spring tension to allow it to move all the way up and back down to the stop motion block under it.
   
6. If you have changed needles, size matters. A larger than required needle allows the knots to rise to the top, where they may have been previously centered vertically.
   

Edited December 8, 2013 by Wizcrafts

[Fat Dog Leather]

Wiz......thanks for the words of wisdom. Tried your points as listed above, during my efforts I did not adjust the bobbin - did verify the direction and using the same needle with no thread problems.

As it stands now both adjustors are wide open with little tension - the knot sitting slightly deeper.

Will attempt 5 as listed with a less frustrated approach this morning.

Once more thank you!!

[Wizcrafts]

In item #5, where I mentioned the tension on the spring on the second adjuster, I meant the beehive spring on the lower rolling disk on the faceplate. The check spring is a separate, but connected item that can be adjusted separately.

Wiz help please!

Sewing on my cobra 4 up to recently with perfect tension on 6oz material. Today it is out of wack with the knot sitting too close to the top. Adjusting the tension springs I have put it out of adjustment apparently not moving both spring at the same rate. How can I get it back into sync?

Would greatly appreciate your advice.

Fdl.

What size thread are you using, on top and on the bottom? What size and point is the needle?

[Fat Dog Leather]

Using 277 top and bottom, 200 needle. This combo has worked excellent for me up to this issue.

Is there a way to reset to factory setting or point zero for these two adjustments.

Again thank you.

[Fat Dog Leather]

Wiz,

Was out of town on my paying job and just got to seriously work on my tension problem tonight.

Finally the stich looks in line with the knot sunk down..... Much adjustment on the springs - moving them in unison 1/2 turn at a time with paint on the nut to keep me straight.

Your assistance was much appreciated!!!!!!

FDL.

[Wizcrafts]

It is unfortunate that the state of leather sewing machines is such that there is no machine means of resetting tensions to a default setting. All adjustments are done manually, testing as we go.

Quilters and embroiderers have it one up on us. There are hand held pressure scales available for quilting and embroidery machines to adjust the top and bobbin thread tensions to a known value, for any given thread. Using these scales they are able to dial in the thread tensions to the optimum setting before they start sewing a project. It would be interesting to find out if these scales can be modified to work on leather sewing machines, which typically require much higher tensions on top and in the bobbin cases.

One might try using a good quality fish weight scale to measure the tensions once a good setting has been found. It might get one into the ballpark, if not on the money. But, the thicker the thread and denser the leather, the stronger the top tension needs to be to pull the knots up halfway. I guess each sewer would have to establish his or her own default setting for their average work, whether it be 4-6 ounce wallets, 8-10 ounce belts, 16 ounce pancake holsters, or more serious 1/2 to 3/4 inch holsters and sheathes with welts. Each doubling in thickness may require increases in the top tension.

There is one sewing machine I have used in the past that can place the knots in a predictable vertical position (up from the bottom layer) almost every time. It is the Union Lockstitch Machine. The take-up arm is designed to pull the thread knots up a distance that can be varied by turning a four sided screw. This setting is separate from the top thread tension disks.