How good is a balanced stitch?

[Gymnast]

I have tried to do some test sewing on two layers of vinyl with a Tex 135 polyester thread. I do have some variation in the balance. Some locks are near the top surface and some near the lower surface. I suspect, that you always will have some variation. I noticed, that sewing in the vinyl I got is quite critical regarding thread tension. An increase in thread tension of 10 % can change the seam from having the locks predominantly at the lower surface to be predominantly on the upper surface. But what can you expect from a good sewing machine?

The picture below have red thread on the bobbin and black needle thread. Stitch length is about 4.3 mm. Would you think the thread tension is too low? Do the stitch got resonable quality? It is a close up photo, so details and errors should show up quite easily.

[kgg]

I think another factor would be the type of needle being used as vinyl can be a bit sticky along with how thick the vinyl is and the type of material as a backing.

kgg

[Gymnast]

The vinyl used here got a glass grid embeded between two PVC foils. It is 600 g/m2.

[Constabulary]

How thick are the 2 layers in total? The total material thickness makes a big difference especially when using thicker thread and larger needles. Its easier to balance the thread knot in thicker materials when using thicker thread and larger needles. If not pleased with the thread knots visibility try a thinner thread and smaller size needles. Or when the bottom seem is not visible on the your product lower the top tension or increase the bottom tension a bit and the knot will move a bit to the bottom side. Or use a 1 size thinner bottom thread.

Edited December 8, 2020 by Constabulary

[Gymnast]

I have measured the thickness using a caliper, and the two layers are 1.1 mm in all. The thread size used here is Tex 135 polyester with a 140/22 needle. And yes, I agree, that it is easier to balance the stitch with more layers of this fabric. Perhaps the variation in hight of the lock is the same, but it is better hidden in the thicker material. Thanks for the adwise on thread size.

You can enlarge the photo to see more details. Would you think that the variation you see here got acceptable quality?

[Matt S]

1.1mm total thickness with T135/V138/TKT20 thread top and bottom is pretty tight. That thread is 0.4mm diameter, so your lockstitch knot is going to be only a little smaller diameter than the thickness of what you're stitching. Any minor variation in material grippiness or thread tension will bring that knot into visibility, and even a minor variation would bring it to the surface. Very few actual makers of stuff (using a lockstitch) would use that combination of thread size in that thickness of material.

To answer your most recent question yes that is acceptable quality but an unrealistic one to expect to be maintained.

[Gymnast]

I have studied two manufacturers of gymnastics mats (or other foam shapes) with covers, that use this type of vinyl for with basic straight stitch seam. So it is mostly not for topstitching, and therefore appearance do not matter. I noticed the thread size and it is mostly Tex 90 or perhaps Tex 70 - so you are right. However I have also seen such mats after 10 to 20 years of use. Then the typical problem with the seems are that a thread is broken, so a seam starts to unravel. The other problem is, that the thread of the seam starts to cut through the vinyl. In both cases I should guess, that a thicker thread should increase lifetime.

Edited December 9, 2020 by Gymnast

[kgg]

1 hour ago, Gymnast said:

Then the typical problem with the seems are that a thread is broken, so a seam starts to unravel. The other problem is, that the thread of the seam starts to cut through the vinyl. In both cases I should guess, that a thicker thread should increase lifetime.

To help with broken thread in seams and reduce the thread from cutting through the material I would consider the seam construction possible use of a reinforcing backing material. Maybe using a semi flat or flat seam construction. Just a thought.

kgg