Stitch strength heresy - Lock vs Saddle

[AlZilla]

So, I'm going to commit heresy. I've had time to ponder this while spending about 8 hours hand stitching a project.  Here I go ...

I don't believe that the saddle stitch is any "stronger" than the lock stitch. We often see it said, but I just don't see any reason for it.

Hear me out - any given stitch length is the same whether it's locked by machine, or a hand sewn saddle stitch. If the thread is the same, the strength is equal. Each stitch line has the same number of stitches and, thus the same length of thread.  The bottom thread on a saddle stitch goes all the way to the other side. The bottom thread on the lock stitch goes half way, thens around and goes half way back. So, everything is equal.

I can see the argument that if I break one side of a saddle stirch, I still have the 2nd thread running end to end. That's not "strength", it's durability.

I'm willing to be wrong.

[fredk]

Its a matter of semantics

[DJole]

In the lock stitch, the threads are pulling on each other. In the saddle stitch, they are only pulling on the leather. 
I wonder if that might make a difference? Of course, it's only speculation without somebody putting the threads to a test on an industrial testing machine. 

[friquant]

In studying knots and rope, the strength of a rope is greatest with no knots at all. Adding a knot puts kinks in the rope, and the rope is weaker with the knots/kinks. I think of it as a stress concentration factor, as cutting a notch in a board would be.

For knots and rope, each particular knot has a strength rating, some percentage of the original rope strength that remains when the rope is tied with that knot. But thread being as thin as it is, I don't know if it's subject to the same rules about kinks. 

A few months ago I tried out a force tester that would record the maximum strength, and I broke a few threads with it before i sent it back. I wasn't really studying the effect of the knots at the time so I don't have any data on that front. 🤷‍♀️

 

[chuck123wapati]

On 10/4/2024 at 8:41 PM, AlZilla said:

So, I'm going to commit heresy. I've had time to ponder this while spending about 8 hours hand stitching a project.  Here I go ...

I don't believe that the saddle stitch is any "stronger" than the lock stitch. We often see it said, but I just don't see any reason for it.

Hear me out - any given stitch length is the same whether it's locked by machine, or a hand sewn saddle stitch. If the thread is the same, the strength is equal. Each stitch line has the same number of stitches and, thus the same length of thread.  The bottom thread on a saddle stitch goes all the way to the other side. The bottom thread on the lock stitch goes half way, thens around and goes half way back. So, everything is equal.

I can see the argument that if I break one side of a saddle stirch, I still have the 2nd thread running end to end. That's not "strength", it's durability.

I'm willing to be wrong.

take one piece of thread and try and break it then, take two pieces of the same thread and try and break them.

I will add saddle stitching into drilled round holes defeats the thread's ability to lock together, the leather slit and the tension it provides is part of the process that makes saddle stitching a stronger and better choice IMO.

 

[TomE]

1 minute ago, chuck123wapati said:

I will add saddle stitching into drilled round holes defeats the thread's ability to lock together, the leather slit and the tension it provides is part of the process that makes saddle stitching a stronger and better choice IMO.

 

That's an interesting point, Chuck.  It seems the ability to use a sewing awl is a dying art, driven in part by the ability to market expensive punches and irons.  I've been an advocate for the efficiency, versatility and esthetics of awl sewing - holes always line up, can sew odd shapes that are difficult to punch, the hole size matches the thread.  I'll add strength of the stitch to the list.

Strength is tested on a regular basis with horse tack.  I haven't seen many examples of failed stitching.  It's usually the leather breaking where it wraps around hardware.  I have seen linen thread rotted out after many years.

 

[chuck123wapati]

12 hours ago, friquant said:

In studying knots and rope, the strength of a rope is greatest with no knots at all. Adding a knot puts kinks in the rope, and the rope is weaker with the knots/kinks. I think of it as a stress concentration factor, as cutting a notch in a board would be.

For knots and rope, each particular knot has a strength rating, some percentage of the original rope strength that remains when the rope is tied with that knot. But thread being as thin as it is, I don't know if it's subject to the same rules about kinks. 

A few months ago I tried out a force tester that would record the maximum strength, and I broke a few threads with it before i sent it back. I wasn't really studying the effect of the knots at the time so I don't have any data on that front. 🤷‍♀️

 

That's just it a saddle stitch doesnt create a knot while a lockstitch is basicly a series of knots. 

Visualize your threads. Saddle stitching is basically using two threads spiraling them together with leather in between with no tension built by the threads pulling against each ohter. while lockstitch is two pieces of thread wrapped around each other in every hole, pulling against each the oposing thread on the other side of the leather 

[chuck123wapati]

5 minutes ago, TomE said:

I haven't seen many examples of failed stitching.  It's usually the leather breaking where it wraps around hardware.  I have seen linen thread rotted out after many years.

 

This is the reality, and i agree completely. The sewing machine is one of the greatest inventions man has ever made IMO and the lock stitch has worked for a long time too. 

[Cumberland Highpower]

Saddle stitching mostly still exists for either of 2 reasons:  

1) Novelty

2) Poverty.

Novelty as in Hermes or other high end makers that are selling the work of skilled artisans and a high end/luxury item.

Poverty as in you can't afford a stitcher, yet.

Even when I hand stitch that rare item I don't use a saddle stitch anymore. (I use a speedy stitcher).  the stitches look about the same and the strength is close enough.  (Your hands are only going to last so long, don't wear them out fiddling with stitches).

There are a very few times  when saddle stitches are used by an equipped shop.  Repair, someone just wants it done a certain way or reproduction of goods designed before machine stitching.   

Edited yesterday at 02:28 PM by Cumberland Highpower

[Digit]

I have no experience with hand stitching, but a possible weakness with a saddle stitch might be that you keep pulling the same thread through the leather, abrading the thread and making it slightly weaker with each hole you pass. By the time you reach the fiftieth hole, the thread has been pulled through fifty holes.

With a (machine) lockstitch only a short amount of (top) thread gets pushed through the hole and pulled back, while the bottom thread doesn't get pulled through at all. So any bit of the top thread at any moment in time has been pushed through the leather only a couple of times and so has only worn down a little bit.

Increased thread abrasion with manual stitching is offset by typically using thicker thread sizes as far as I can tell (so they there is more material to abrade before the thread becomes too weak) and waxing the threads for lubrication (so they abrade less when pulled through holes).

On the other hand, the threads in a lockstitch basically make a 180 degree U-turn and as has been said before, that sort of a concentrated pulling point might be a weak spot.

That said, now I wonder where a thread usually breaks when it does: in the exposed bit along the leather (in which case it doesn't really matter which stitch type you use), or in the hidden bit inside the leather where the threads are either locked (lockstitch) or where they pass each other (saddle stitch).

Also, to be fair, one should compare apples with apples: so we should compare different stitch types using the same thread type/size and leather and that could be hard. Running a thick waxed thread through a machine would require a heavy duting sewing machine and using an unwaxed machine thread while hand stitching for any serious length would probably wear away the fibres in the thread...

In the end I think both stitch types are comparable in strength and it would largely depend on thread thickness, thread material, and the way in which an item is used how soon a stitch would fail.