Leather sag

[Woodland Artisan]

First of all, I know nothing about leather.

I'm in the prototyping phase of a custom, period chair that will have a leather seat.  Think of a directors' chair in how it's (usually) canvas seat is stretched between the 2 short sides of the rectangular piece.  Same type of idea in how this chair will be done except with leather.

What I'm wanting to know is about how much 'stretch' or sagging the leather is going to have initially.  This will give me some idea of where to place the stretchers (pieces of the chair on each side where the leather will be attached) so that it's not too low and hit the front, lower-placed wooden pieces of the chair.  Obviously (or not?), the leather will stretch more as time goes on but I'd just like to know what to expect initially.

The leather rectangle is going to be about 3 feet long x 16" wide.  It'll be attached to the chair along the 16" long sides.  Thickness?  Type?  Weight of the person is going to be probably no more than 150-160 lbs.

In woodworking, we have formulas for determining how much sag given the type of wood, dimensions and weight upon it.  Is there something similar for leatherworking?  If not, anyone care to make an educated guess?

Normally, I'd make this type of chair with a wooden seat but this is a custom order and I've never tried using leather like this.

[jcbanner]

If there are any formulas for how much leather will streach, I'd love to hear them myself.  In my experience, every piece of leather is diffrent,  depending on the growing conditions and tanning processes the hide went through.  In one example, think juvenile vs mature wood, the fibers aren't as dence or packed as tightly.

But leather will streach, no matter what the factors are.  One way that I'll compensate for that is to laminate the leather with fabric, or sometimes even a piece of canvas laminated between two sheets of leather, with top grain out (for appearance).

I think something like that could be used nicely in this case.  Cut your 1st sheet of leather to your size, then spray a contact adheasive into it and some canvas, lay out the leather on the canvas and roll it smooth. after triming away excess cloth, repeat that with a slightly larger piece of leather, with say, a one ince margin on the front and back sides.  this larger piece will be the top after folding the extra margin over to the back in running a stich or two down the length to hold it in place.  the glue may or may not hold, but the stiching is what will hold it together, think quilted armor, the stiching makes it stronger.  I'd think doing this, 6oz leather would be good.

Anyone out there with more experince know if theres a better method?  Or that confirm for me if this would work? I've never really had to make anything that holds much weight before.

[escherblacksmith]

There is not really any math that will work that out.  But, the cut you make it from will have an impact.

Belly is much stretchier then the shoulder or butt.  But, enough stress (and moisture) and all leather will stretch.  your best bet would be to experiment with the shoulder (smaller pieces, cheaper) and play with multiple layers.

[DeadBishop]

My advice would be that whatever you do, you should reinforce it in some way.  Simply using the leather by itself would probably give you more sag from stretching over time than you'd care for.

[crazyrennie]

I will concur with the comment about belly stretching.

I am going to assume(I hate doing that)that you will be treating the leather prior to cutting?

[Taffy Saltwater]

Maybe some belt-like straps underneath for additional support?

[Woodland Artisan]

Thanks for the help, everyone.   I've been in contact with a leather worker forum and some of their members too.  I'll keep all of it in mind when this project gets to that point.  I'll not be doing the leather working myself but it's good to know what to expect or to talk with the leatherworker about.

I think some sort of heavy canvas straping on the underside of the leather would help, hidden and be (at least somewhat) period appropriate.  That and having pre-stretched, heavy, and non-belly leather helping too.

[jcbanner]

be sure to keep us updated on how it turns out, and we love pictures.

[Woodland Artisan]

Will do ... although the leather seat portion of that project is till some months off.  The chair is to be heavily carved and that'll take a couple of months, at least, just for the legs.  But, I'll get pictures as I go along with it.

The next little project also has some leather to it as well but it's just an addition to my demonstration area and I think I can do it myself.  It should be really simple as long as I can find suitable leather for it.  Once I get that done, I'll take pictures of that too.  Not sure what it's actually called but I've seen paintings of it somewhere.  Basically, just a piece of leather stretched over the ends of a tripod of saplings to hold water in the 'pouch'.

But, for this weekend, I'm taking some time off and playing around .... finally getting to the "flaming balls of death" scrapwood trebuchet.   Everything is ready except the final touches to the cardboard castle to be laid waste to.  It rained pretty good here the other day so the field isn't likely to burn out of control ... there should be nice fog in the mornings for some great footage of the event ... and I'll have 3 good cameras rolling so maybe I'll get good coverage before the entire treb goes up in flame. ha!

[groomporter]

I've got a Civil War era-styled folding chair and the craftsman who made it took a single piece of heavy canvas and glued it to the entire back side of the leather seat to help prevent it from sagging/stretching

[jcbanner]

I don't know if your still looking for input on this, but over the weekend, I saw a folding wooden chair with a leather seat.  it was a relatively light weight leather, I'd say around a 6oz leather.  the chair has been getting constant use for some time, and there is not all too much sag with it, only enough to be comfortable.

There was no canvas backing on it, nor were there extra straps added to make it more ridged, all that had been done to the leather was have the edge folded over and stitched in place. I didn't think to look much closer then that, but I believe that the seat was attached with a pocket on either end that slipped over wooden bars on the side.  (Think like a flag that slips over the flag pole instead of being clipped to a rope)

[NoBill Lurker]

I don't know if your still looking for input on this, but over the weekend, I saw a folding wooden chair with a leather seat.  it was a relatively light weight leather, I'd say around a 6oz leather.  the chair has been getting constant use for some time, and there is not all too much sag with it, only enough to be comfortable.

There was no canvas backing on it, nor were there extra straps added to make it more ridged, all that had been done to the leather was have the edge folded over and stitched in place. I didn't think to look much closer then that, but I believe that the seat was attached with a pocket on either end that slipped over wooden bars on the side.  (Think like a flag that slips over the flag pole instead of being clipped to a rope)

You know, I've seen something like that sold at Tandy Leather.

Folding Stool Kit

(you can also get the legs separately)

[jcbanner]

thats not quite what I was talking about. Artisan's description of the chair he's making is a similare type of chair like I was talking about