Is leather stronger when laminated with an additional layer of leather?

[Northmount]

19 hours ago, nstarleather said:

Plywood and OSB orient the grain of the wood to cross and create the strength.   If you were to create a laminate using the grain parallel as opposed to perpendicular, you wouldn't get the same strength.   Leather grain isn't the same thing.

It would be interesting to see if there are any bow makers here and what their comment and experience would be.  Their laminations are all oriented along the length of the bow.  Maybe it has more to do with how much spring.  Off topic, but interesting.

Tom

[TinkerTailor]

32 minutes ago, northmount said:

It would be interesting to see if there are any bow makers here and what their comment and experience would be.  Their laminations are all oriented along the length of the bow.  Maybe it has more to do with how much spring.  Off topic, but interesting.

Tom

Wood is unidirectional. It needs to be in the direction the tree grows. If you take a sheet of plywood that is 5 layers thick, it will be much stiffer and stronger parallel to the grain in the direction that has 3 layers going the same way. Any laminations with the grain direction the wrong way will crack. In addition, as moisture content changes wood only expands and contracts widthwide and not lengthwise. Having the expansion and contraction of the layers opposing each other can lead to glue joint failure. This is one of the reasons plywood left outside delaminates. Bowyers laminate in other omnidirectional materials like rawhide, sinew or fiberglass to counteract woods nature to split along the grain.

 

The long and short of the leather  laminate question is this:

• Full thickness, unsplit leather is stronger than split of equal weight, as listed in several textbooks. removing 1/3 of the thickness from the backside reduces the strength by half.
• Leather fibers are omnidirecional and do not run parallel like wood, meaning comparisons are not that accurate.
• Glue does not increase tensile strength. It maintains a cohesive bond so the 2 layers act as one layer. (there is engineering data for this.) Wood laminates are stronger because wood is unidirectional and 2 pieces with slightly differing angles to grain structure will triangulate each other when bonded. The omnidirectional nature of leather fibers intertwining means they do not have this property.
• The data supports that the surface grain does not add to strength. It does add to durability and resistance to contamination(which are a different topic), but not strength.
• The data also supports that the grain is harder to bond to, meaning face to grain glue joints are weaker and as such, a laminate of this type is likely weaker once the glue bond lets go,  than a cohesive laminate that acts as a single layer would be.

With that said, and assuming we are talking about unflawed leather, a belt made with 2 unsplit strips of 5 oz glued together back to back should be just as strong as a belt made from unsplit 10 oz. If it is stitched as well as glued, the stitching will add a small amount of strength but also pierce the leather as mentioned so to be a fair comparison the 10 oz would be need be stitched as well. In this case they should also be the same.

A belt made with 2 layers of hide split to 5 oz will be weaker than a belt made from unsplit 10 oz. but likely are the same strength as leather split to 10 oz.

As to the existence of the grain protecting the leather, longevity is a different question to strength.

Edited December 23, 2016 by TinkerTailor

[TonyRV2]

On 12/22/2016 at 10:07 AM, TinkerTailor said:

Do you have a link for that reference? i would like to add it to my library./

I looked ain a bunch of books for the section i remembered reading on drive belting, but I could not find it. I have read that they shaved/sanded/buffed the grain off when they layered skived hides to make thicker heavy duty drive belting. They would arrange  them like a deck of spread out playing cards, with the hides half overlapped to get more thickness. The glue joint was not as strong grain to flesh as it was flesh to flesh, hence the removal of the grain.

Also, as to the original question, Leather belting was never stitched only glued. The sections of belt were joined with stitching or clips, but the pieces are way longer than a hide is. The individual hides were glued together. I am sure if glue worked good enough here, it will hold up the that dirty hairy gun on yer belt

I also have a few scientific journals that talk about leather tensile strength from the early 1900s but they are way too dry to read right now......

Here's the link to the google book.  The explanation basically starts on page 182, section 26.
 

https://books.google.com/books?id=QV8IAAAAQAAJ&pg=PA183&lpg=PA183&dq=which+is+a+stronger+material+the+grain+side+or+the+flesh+side+of+leather?&source=bl&ots=H_oOqbEpfM&sig=oOIV8XoJqE_IGMlnreVk_-wOKlI&hl=en&sa=X&ved=0ahUKEwiYjffGlYjRAhUpqlQKHR91BdUQ6AEIRzAI#v=onepage&q=which is a stronger material the grain side or the flesh side of leather%3F&f=false

 

I consider myself a student of one of the renown sheath makers of our time, Paul Long, having purchased and studied all of his DVD's time and time again.  Now according to Paul, when gluing two pieces of leather together PROPERLY, flesh side to flesh side, the bond will be so strong that any attempt to tear it apart will result in the leather fibers ripping before the glue bond gives way.  This would lend credence to the idea that laminating two pieces of leather together would likely increase the tensile strength.  I say likely only because I haven't seen or heard of tests of this sort actually being performed.  Paul's idea of 'properly', to which I have personally subscribed, is to put two coats of Barge on each surface when doing flesh to flesh.  The first coat is allowed to tack up and soaks into the fibers, the second coat then lays atop the first.  So I believe that the glue bond does not diminish the overall strength of the leather although this does not really speak to the quality of finishing the edges of the leather in order to prevent affects of weathering on the material.  To summarize, the tensile strength (the degree by which the leather could be stretched before breaking is likely increased as it would be no different than using two straps connecting two point as opposed to one.  The shear strength, that is ripping one layer from the other, would remain unchanged as compared to a single strap subjected to shear forces.  Thats my story and I'm stickin' to it, at least until someone else changes my mind.

[Chief31794]

Boy, this got into detail, I ain't got all that science, but what I've observed over the years is that a belt with two layers will hold a 1911 weight pistol with less "sag" than a single layer belt of the same thickness, that's what I based my comment on. I don't make belts for use on machinery so that may be different, but when someone wants a belt for carry, I highly recommend a double layer belt as they last longer and sag less under the same use and weight carry.

Chief

[bikermutt07]

In my experience a single layer of uncut non stitched leather will last a cow a lifetime.

[TonyRV2]

2 hours ago, bikermutt07 said:

In my experience a single layer of uncut non stitched leather will last a cow a lifetime.

This sounds udderly reasonable and eliminates all the bull.  

[HENDREFORGAN]

All good technical stuff and don't doubt a word of it . . but . . I'll take a more down to earth and practical point of view.

Yes - technically - punching holes in hide leaves an Achilles Heel but then again the thread you stitch the pieces with will be waxed and a hell of a lot of that gets pumped into the holes which, with the frictional heat of the process, will be absorbed by the hide.  That will prevent more ingress of water than into the hide itself.  Yes, old harness straps are often dry and the stitching and their holes broken but that isn't a fault of the system, it's a lack of maintenance instead.

Glue?  Sorry but I, possibly many others, used this when we were bumbling amateurs simply because we knew nothing else.  Industry stills uses the method today but, you pays you're money and make your chioce, how many cheaply made items have we all seen fall to pieces due to glue failing?  Give me a good quality thread, fresh needles and a block of beeswax and my stitching will be capable of outlasting any owner of my work.

So correctly stitched a laminate of two pieces will be stronger than one thick one . . but will it look right?  Will it convey the image of quality?  Not on some products.

 . . and sorry but it's sueded and not suede.  Yes, there are leathers with particular textured nature with open pores chosen to be sueded but suede is typically a definition of finish and not the hide itself.

[JLSleather]

15 minutes ago, HENDREFORGAN said:

sorry but it's sueded and not suede.  Yes, there are leathers with particular textured nature with open pores chosen to be sueded but suede is typically a definition of finish and not the hide itself.

I always get a 'kick' outta them folks debating to use "leather" or "suede".  Bazillion messages asking if holsters should be lined with suede.  TIP:  If you don't line your tooling leather holster, then the inside already IS "suede"

 

[Dwight]

1 minute ago, JLSleather said:

I always get a 'kick' outta them folks debating to use "leather" or "suede".  Bazillion messages asking if holsters should be lined with suede.  TIP:  If you don't line your tooling leather holster, then the inside already IS "suede"

 

I'd not be a bit surprised if you could not hear me giggling all the way from here.

You are ever so right, . . . and there are a whole passel of folks that want to argue with you, . . . so I'll get out of their way.

May God bless,

Dwight

[HENDREFORGAN]

1 minute ago, JLSleather said:

I always get a 'kick' outta them folks debating to use "leather" or "suede".  Bazillion messages asking if holsters should be lined with suede.  TIP:  If you don't line your tooling leather holster, then the inside already IS "suede"

 

  You've got a  point . . are people actually paying for something that nature provided us?  Very probably.  Suede to me was always cheap hides tarted up to look more expensive.

Nor should one forget that back in the days of shoe making when the lasts were not handed shoes and boots made for a working environment were made grain side inner so that the naturally sueded fibres could be kept heavily waxed to keep water out.  You know . . it still works to keep an old pair of Hush Puppies fresh?

[MADMAX22]

On 12/24/2016 at 0:59 PM, HENDREFORGAN said:

  You've got a  point . . are people actually paying for something that nature provided us?  Very probably.  Suede to me was always cheap hides tarted up to look more expensive.

Nor should one forget that back in the days of shoe making when the lasts were not handed shoes and boots made for a working environment were made grain side inner so that the naturally sueded fibres could be kept heavily waxed to keep water out.  You know . . it still works to keep an old pair of Hush Puppies fresh?

I believe the reason for this including the ability to hold waxes and what not was to hide damage/scrapes/scratches and such. With a roughout boot you can beat the snot out of it then go over the leather with a brush and the marks go away generally. 

Thought suede was a actual finish to the rough side that actually got rid of alot of the "roughness" of using the rough out (flesh side) of the leather. A sanding and milling process, correct me if I am wrong please.  

[HENDREFORGAN]

7 hours ago, MADMAX22 said:

I believe the reason for this including the ability to hold waxes and what not was to hide damage/scrapes/scratches and such. With a roughout boot you can beat the snot out of it then go over the leather with a brush and the marks go away generally. 

Thought suede was a actual finish to the rough side that actually got rid of alot of the "roughness" of using the rough out (flesh side) of the leather. A sanding and milling process, correct me if I am wrong please.  

Yes, having the rough side outermost and heavily waxing meant maintenance could be a lot rougher than similar polishing of the grain side.  Even today if I have to re-oil old leather to rejuvenate it I'll look to work "inside out" as, with usage, the patina on top grain can form a rather effective armoured surface.  Easier and quicker working from the other side.

Remember too that in the days when working mens shoes were grain side innermost that was also a comfort chioce . . very few could claim to earn enough to buy socks and shoes/boots were often worn with bare feet.

Along the lines of your reasoning the process of sueding is used on higher quality hides.  Today we see hides that have been buffed - corrected leather - where the original grain showed defects and the buffing produces a uniform standard.  Often applied to full grain leather but you can be sure some sectors of the leather industry will treat spilt leather the same to try and "tart them up" . . . which neatly brings me back to my earlier comment . . suede = cheap leather "tarted up".

[Rayban]

I'm surprised no one has replied to this.

I say yes, 2 layers equaling 1/4" thickness, will be stronger than one layer at 1/4". Think of plywood, same principle.

I've spoken to several old salt belt makers on this and we all seem to be on the same page.

When glued and stitched together, less stretching, more rigid...much much better than single ply.

[MADMAX22]

15 hours ago, Rayban said:

I'm surprised no one has replied to this.

I say yes, 2 layers equaling 1/4" thickness, will be stronger than one layer at 1/4". Think of plywood, same principle.

I've spoken to several old salt belt makers on this and we all seem to be on the same page.

When glued and stitched together, less stretching, more rigid...much much better than single ply.

Ray I think he started two threads at the same time. The other one got alot of discussion. 

Both threads now merged.

 

Edited February 4, 2017 by northmount
Merged threads