Why do my sheaths twist during assembly?

[PIndelicato]

It seems when I fold over and cement my pouch sheaths together, they always seem to twist to varying degrees. During wet molding I can usually alleviate most of it, but I'm curious if it's an indication of something I'm doing wrong, or if it's just a natural part of the process.

Here is one I cemented last night, and it's one of the worst ones so far. Thanks in advance for any comments!

 

[Ebbtide]

Is the leather wet when you make the initial fold?

 

[PIndelicato]

Sometimes...yes...maybe

I probably tend to do some of the early folding dry, but when I fold it all the way over I try to dampen it in the fold area front and back. I don't really have a strict process that I follow, and maybe that's the problem.

 

[PIndelicato]

Does it have anything to do with the fact that there's tooling/carving on the front and a belt loop sewn on the back? It seems that would affect the stiffness differently in those different areas...

 

[leatherman]

Leather has a grain, the fibers travel in one direction. Leather will, as a result, stretch more in one direction than another.

If you cut out the sheath diagonal to these fibers it will resist being bent on that axis, thus your twist. When I am cutting a lot of pouch sheaths I get the same issues because I go for utilization of as much space as I can on the hide so I get a few diagonal pieces.

On a shoulder of leather, the grain will run across the spine at 90 degrees. So it will stretch more if you pull in line with the spine than it will if you pull 90 degrees from the spine.

Belly leather will stretch in any direction because the animal needs their stomach to be able to expand. Its not good for much at all.

 

[PIndelicato]

Leather has a grain, the fibers travel in one direction. Leather will, as a result, stretch more in one direction than another.

If you cut out the sheath diagonal to these fibers it will resist being bent on that axis, thus your twist. When I am cutting a lot of pouch sheaths I get the same issues because I go for utilization of as much space as I can on the hide so I get a few diagonal pieces.

On a shoulder of leather, the grain will run across the spine at 90 degrees. So it will stretch more if you pull in line with the spine than it will if you pull 90 degrees from the spine.

Belly leather will stretch in any direction because the animal needs their stomach to be able to expand. Its not good for much at all.

Thanks Leatherman, I had never given any of that any thought but it makes sense. I've always just moved my pattern around until I got the least amount of waste, and then cut it out. That would help explain the different degrees of twist I've seen.

 

[sheathmaker]

Something as small as a knife sheath should suffer relatively little from the stretch described by Dwayne (Leatherman). Probably the major cause of your stretch is the tooling on unlined fairly thin leather and proper casing could be the start of that problem. To minimize stretch try the following:

Cut out the pattern and fold it to check just how even and symmetrical the two halves are to start with. Accurately cut patterns are a must.

Use clear packing tape and cover the back (flesh side of the leather)
Case the leather (wet it thoroughly and allow it to return almost to the original dry color). This will give you more uniform moisture content throughout the fibers. Complete your tooling and allow the piece to air dry naturally. Remove the packing tape carefully. Now fold again and see if the tooled side is larger, or longer than the back piece. If so you have had some stretch and this will translate into a twist when you glue it up. If you have left a large enough margin on the tooled side you might be able to trim some of the stretch out of it prior to glueing.

Finally, choosing tight, firm leather to start with will eliminate a lot to the tendency to stretch. Never use belly leather, or "flanky" loose fiber leather.
You will never be satisfied with the results.

Also remember the lighter the leather, the more the stretch. This is because light weight leathers are split from heavier pieces and the part that is split off carries with it part of the strength of the leather and its ability to resist stretching.

Paul

 

[PIndelicato]

Thanks Mr. Long! I just used up the last of my Tandy-sourced 8 oz 'shoulder' (I always thought it was junk), and this sheath is the first I've made with the Wickett and Craig Double Shoulder I bought a while back (I think it was 7/8 oz???)

Is the packing tape something that you recommend doing all the time, or just as an exercise to determine stretch? Aside from the tape, I try to follow the casing methods you describe. One problem I would have though, and this was with the Tandy leather so perhaps that was part or all of the problem, but during the warmer, drier months here in AZ (110+, 15% hum), this casing method didn't work very well and I would have to keep re-wetting the leather in order for it to take the tooling. Shortly after returning to it's natural color, it would become hard and not want to take stamping.

All of my methods come from the Chuck Burrows DVD...I draw the pattern, then fold it in half to cut it out so the pattern is even and accurate. After I actually cut it out of the leather, I suppose I don't pay too much attention to that as everything is 'built' off the front, so that once the front edge is determined, any excess is trimmed off the back to match (if that makes any sense at all, it's early and I've only had one cup of coffee this am!)

Thanks for your comments and input.

 

[sheathmaker]

I only use the packing tape thing when I suspect there will be a stretching problem and because I line everything I make, the lining makes a perfect and permanent replacement for the anti stretch tape, so no, I don't use it often.

Using a spray bottle to re dampen the leather is perfectly acceptable, and I do that frequently as well.

Certain stamps will by their very nature be more prone to causing stretch. The all time favorite basket weave stamps are certainly in this category. This is a case where the "almost dry" casing technique is of benefit, and also a case where selective spritzing with the spray bottle will probably be necessary.

Finally there is a little trick involved in the glue up process. Set the edges together evenly at the mouth of the sheath and then at the toe of the sheath and then "fill in" the contact from both ends to the center, kind of massaging as you go. This is will cause the leather to "eat itself" (an old saddle maker term) meaning the fibers will compress and flatten out when the contact is made and it will minimize if not eliminate the twist. Twist is caused when one side or the other is longer and it is still attached evenly at both ends. The longer side has to go somewhere so it becomes a twist.

I assume you wet form after the sheath is fully assembled and stitched. You can actually massage a little bit of twist out in this process as well.

Paul

 

[PIndelicato]

Thanks again for all of the input, Mr Long. I have been un-twisting during wet molding, and it works to varying degrees. I wet molded this one last night, and it's better than where it started, but it re-twisted to some degree while it was drying overnight

I will try your glue-up trick on my next one, I hadn't heard that tip before but it sounds like it would help with the problem I've been having.

Thanks again!

 

[leatherman]

quoted for relevant content.

Something as small as a knife sheath should suffer relatively little from the stretch described by Dwayne (Leatherman).

Paul

I wasn't referring to stretch in reference to the twist of the sheath, it was just illustrating the point about leather grain.

Take corrugated cardboard for example. Fold it in line with the corrugations and its easily done, fold it in a diagonal and it wants to twist. When I cut a folded sheath out of line with the grain I get a sheath that doesn't want to fold straight, when cut in line it folds straight and easy. I did this experiment with the last 100 sheath order I did that had 7/8oz leather (small edc sheaths) and it was very consistent. And irritating. Forcing a few dozen sheaths to your will can wear on the patience.

A couple of years ago, under great pressure to produce a better product, Tandy/Leather Factory went on the search for a better tannery. The result of that is quite nice. For the most part I use Double Bends, and #1 grade Double Shoulders, almost no waste. The new tannage is light years better, nice touch, smooth face, very good flexibility, no hard spots and fewer if any scars and bug bites. I like being able to dig through the stacks at the Leather Factory and find what I want. Lately the only disappointment has been when they run out of a particular type. If I get something home and am not happy with it, I can return it and get a replacement immediately.

This leather has been torture tested in some of the worst environments, much to my chagrin and the leather has come through with flying colors. Just dont go cheap, pick through the piles, and you wont be disappointed

 

[rayban]

I can't wait to use it on a knifer...."don't get your sheath in a twist!!"

 

[Josh Dabney]

Paul.

These guys are the experts in the sheathmaking and leatherwork arena. However something seems to me to be lost on me in the technical responses given thus far so I thought I'd give it a shot at a simpler explanation of my opinion.

Stamping , carving, dying, and grain, all may effect the leather but are basically irrelevant to your problem. IMHO, Even given the perfect leather running with the grain, no tooling etc... you'll experience the exact same problem because we can't fold and mold the leather like a machine. Uneven pressures and stresses on the leather cause the twisting.

The solution is a simple one best explained with a pic.

Once your all glued up and discover the twist work the body of the leather like this slipping the body part over the welt part. You may need one side or both just depending on how bad the twist is. Get it nice and straight then clamp it up with spring clamps.

Problem solved.

-The sping clamps will put big dings in the leather so I use some heavy weight scrap pieces under the tips of the clamps.

As a side not I've also experienced the same twisting action while stitching the sheath. Just hand bend it straight as you go and it'ss be fine also.

Hope this helps you out, Josh