Wrinkles on pouch flap

[TargetRockLeather]

When I make something like a pouch with a flap, or a strap or anything that has a sharp bend, the leather wrinkles when the flap is opened. When I first made the flap, I moistened the leather so that it doesn't crack. It looks great while it's closed, nice and smooth. After it's dry, and any time after that, when I open the flap, it resists being straightened out and the finished side of the leather wrinkles badly. I've tried using a generous amount of neatsfoot oil to make it more flexible, but that doesn't help. I was wondering if anyone has any tricks for dealing with this. The picture shows an example of what I mean.

 

[battlemunky]

Great question. Unfortunately, I don't know the cause or the solution. I don't see it on any of my stuff though and I have no idea what I could be doing differently. What kind of leather is it? I use mainly HO full sides but have used some Tandy double shoulders and don't see it. Is it belly perhaps? Outside of the cut of leather, I'm kind of just here to see an answer myself...

[Ole South]

If you wet formed the flap and it has any thickness (greater than 3-4oz or so) or even worse a lined flap... then you create an internal vs external diameter differential*.  Meaning the inside length is shorter than the outside length and when you straighten the flap, the excess dimension HAS to go somewhere... so the long side lifts into a wrinkle or wave.  The converse applies if you DON'T "form the arc" when gluing a lining to a thicker top piece or if you don't stretch (wet form) the piece.  In this case, both sides have equal length and if one won't stretch then you'll get wrinkles when the flap is closed (on the inside) due to the flesh side (or lining) lacking the ability to compress enough to compensate for the topside's resistance to stretching.

Work around?  Find the happy medium about mid-way of the bend when making the flap if you're using a lining or don't wet form the fold completely closed or choose materials that have the needed ability to stretch and/or compress.  The stretch vs compressibility (compression ratio) of the material(s) you're using is the primary factor in this equation.  Remember when wet forming leather you are removing some or all of the compression ratio of a piece of leather and the thicker the piece the greater the I.D. vs the O.D. (Inside Dimension vs OUTside dimension) regardless.

This is also why you may have seen posts on the forums about calculating gusset length of a bag.  Basically the same issue... but exaggerated because not only are you dealing with material thickness (gusset, belly and back) but also how much of a seam allowance is allocated for the bag and the stretch/compression of each piece.  Add in an inside seam (hidden) vs an exposed seam and the calculation gets way more complex.  This solution is a bit easier if you've measured long... just cut off the excess.

* a good example of this is to grab a inch thick stack of paper from your printer or copier and bring the short edges to each other... the top sheets will be way shorter than the inner-most sheets even though they are the same length when laying flat.

Does this make sense?

Edited March 15, 2019 by Ole South
elaboration

[TargetRockLeather]

3 hours ago, Ole South said:

Does this make sense?

Actually it makes perfect sense. The leather I'm using is at least 7-8oz. I just realized you can't tell what the size of the pouch is from the picture. The flap is about 2" wide and 3 1/2" long including the bend. It's not lined but it is rather thick. I thought I was doing the right thing by wet forming the bend. But after reading your explanation I realize I might be shooting myself in the foot. If I understand your suggestion correctly, you're saying to go ahead and wet the leather but only bend it about half way and let it dry that way? The way I did it the flap was fully closed. Or maybe I should try not wetting it at all? Thanks for the quick response.

[Ole South]

Make a prototype without wet forming and test.  If it's too stiff, skive where you want it to bend a bit thinner the width of the flap.

[TargetRockLeather]

Skiving is a brilliant idea. I never would have thought of that. I’ll do a prototype like you said and let you know how that goes. Thanks a lot!

[Bolt Vanderhuge]

Instead of water use Neatsfoot oil to wet form it. You will want a generous amount of NF on the flap enough that is will remain soft in the bend area. After the NF has soaked thru all the fibers you can start forming it to the bend you want. When straight there will still be a little bit of leather that bunches up but it does not look as bad nor does it creat any long term cracks that tend to form over time when water is used to wet form it.

Edited March 17, 2019 by Bolt Vanderhuge

[Bob Blea]

Do you happen to put a lacquer type final coat on these flaps?  I've had this happen when using lacquer based finishes (like NeatLaq or Wyosheen) and I put too thick a coat on it.  The surface becomes pretty rigid and it can wrinkle that that.

[TargetRockLeather]

5 hours ago, Bob Blea said:

Do you happen to put a lacquer type final coat on these flaps?  I've had this happen when using lacquer based finishes (like NeatLaq or Wyosheen) and I put too thick a coat on it.  The surface becomes pretty rigid and it can wrinkle that that.

No sir. Only neatsfoot oil. The surface is rather rigid but that is caused by the wet forming of the bend. Once it dries the leather is more rigid.