Leather sag ?

[WoodlandArtisan]

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.

[TomBanwell]

This is very hard to quantify as leather varies so much. The general rule I've followed is to make the seat as taut as possible. If the seat sags too much you just have to make it over again.

[UKRay]

This is very hard to quantify as leather varies so much. The general rule I've followed is to make the seat as taut as possible. If the seat sags too much you just have to make it over again.

I'd agree completely with you Tom. Each leather type has a different 'sag factor'. Leather thickness and where it comes from on the hide are also critical factors and even the species it comes from can affect stretch.

Think: veg tan and chrome tan / 2oz and 12oz / elephant skin and goatskin / shoulder or belly - IMHO the initial question probably needs to be re-phrased. In other words not so much about sagging but maybe more about the best sort of leather for the job. When that is determined the sag factor may be a little easier to understand.

Edited October 2, 2008 by UKRay

[celticleather]

I know some folk who'd probably appreciate some advice on saggy seats and bellies!

[nwolcott]

How about backing the leather with fiberglass cloth, or sandwich the cloth between two pieces of leather? That way the fiberglass would provide the support and you could use just about any leather you want. To find fiberglass cloth try a boat shop or Google search.

[WoodlandArtisan]

Thanks for the information so far, everyone. If there's any more, please continue on.

I won't be making the leather seat myself, of course. I know nothing about it and will leave that up to someone else later, when that time comes (I'm months away from that stage), to supply a seat. I'm just trying to determine where to place the wooden stretchers that the leather seat will attach to so that it won't immediately "bottom out" so-to-speak. Over time, I guess it will and will either need to be replaced or repaired.

I think the consensus is that any leather is going to stretch to some degree depending on thickness and type of leather used. Maybe even some lamination process with other materials to help slow that down. Very interesting. But, like I said, I won't be doing it myself, but at least it's good to know for when I'm looking for a leather-person to do it.

[8thsinner]

I would suggest simply prestretching the leather. I do that for all of my braid work now and theres virtually no stretch once it's finished.

Just wet the strips for an hour or so in warm water then pull them around something smooth edged but with a little grip. For thinner laces I use a sigg bottle with a speckled sort of finish, this grips well enough.

Make sure you are not pulling it as tight as it can go but close to it.

Once it's dried leave it a day then repeat the process.

Usually by the third stretch you won't be able to stretch it much more without breaking it.

When you are braiding after this the leather is a little less forgiving but the end result lasts longer by far. And you definately should use some sort of braiding soap...