Understanding Stretch With Veg Tan Leather

[csolar]

I'm a woodworker/furniture maker and I've recently started using leather straps to weave seats for chairs and benches. I like the look and feel, but would like a little more confidence about the material's long-term performance. My main concern is with stretch; I don't want a seat to be blown out after a couple of years of use!

Does vegetable tanned leather just keep stretching and stretching as it's loaded, or does it tend to "break in" initially and then stay relatively stable? If the latter is the case, could I pre-stretch my straps somehow, so the initial elongation is dealt with before I weave a seat? I saw a mention of pre-stretching straps used for saddle stirrups (so the L&R stirrups stay the same length), but I don't know how it's done.

(For my first couple of projects I bought plain 8-9oz tooling sides from a local store. I cut these into straps 2" wide and then dyed and sealed them. Going forward I plan to buy pre-dyed hides, specifically 8-10oz English Bridle from Wickett & Craig. My chair seat is about 20" x 24" and the straps are spaced about 3/8" apart. It's a pretty dense weave -- 16 straps in one seat.)

Thanks for any info,

Chris.

[Tree Reaper]

Chris;

You would normally wet the leather straps, stretch them leaving them stretched as they dry.

How much stretch will be trial and error for the leather you have.

[TinkerTailor]

One thing to consider is that straps cut from different areas of the hide stretch differently, so it would be best use the straps as they sat in the hide. Keep them lined up after cutting and make all the parallel straps for each direction of the weave from the same area, just cut them all to length and spread them out a bit. This will help keep stretching uniform and prevent one strap from stretching more than the rest. If you put a strap from the belly next to one from the back, the belly will sag alot more, and not be comfortable to sit on.

[csolar]

Thanks for the info so far!

That's a great suggestion about keeping the straps together. On my first chair I was just fixated on maximizing yield from the hide, so I was cutting straps from all over the hide (including belly), in different orientations, and not keeping track of what came from where. I have since learned to avoid the belly section for this application.

I've set up a little test here in the shop: I took a leftover strap and put a set of marks on it, 20" apart. I fastened the top of the strap to the wall and have 15lbs of weight fastened at the bottom end. I'm keeping a daily log of the distance between those marks, both when the strap is loaded and unloaded. Hopefully that should at least answer my questions about (a) does it keep stretching and stretching or does it stop at some point ( how elastic is it - how much does it rebound when the load is removed.

Chris.

[slipangle]

As you've already mentioned, the belly area stretches most. Theoretically, the area of the hide with the least amount of stretch is the leather closest to the spine, and cut parrellel to it. These backs are the most desireable sections for many applications so they are often bought up by the high end commercial users and often aren't even included on a "standard" hide.

But for something that has to sustain the weight of the typical human being, I would try to source the straps from that area of the animal, if you can find them.

Second choice would be as high up the hide as possible, and only cut parrallel to the spine.

Pre-stretching the straps might not be a bad idea. But I would think that if the straps were of a high quality, and thick enough, that step shouldn't be neccesary.