I'm basically copying and pasting this here from my post on another forum. Hopefully others can learn from my mistakes. It's a but long but stick with me, I'd rather give more explanation at 1st and avoid extra questions later.
Looks okay at 1st.
But, things aren't right. I always try to make a template to play with how things go together when making something I haven't made before. The template worked out fine. I also try to do a "proof of concept" made of material that is either sacrificial or that I have a lot of.
In this case I wanted to make this of thicker veg. tan but don't have much. This leather looks really nice, I have made shoulder slung shot pouches of it before, and I have quite a bit of it. Because it is thin I used some scrap leather that is thicker and almost cardboard stiff for the belt loops so the bag doesn't flop in use.
So, everything worked out with the template. I carefully traced and cut my pattern with the leather. And tried my new stitching clamp.
The clamp is one thing that went right, it makes things a lot easier,
But here is the first minor problem. The linen thread has a little end sticking out the side where more fiber was added while spinning the thread. I hoped it would land in a hole, nope, hoped wax would hold it down, nope. Not sure what if anything can be done about it. Minor problem compared to the rest.
Everything lined up nicely with my template. But, that was thin cardboard, the leather is half again as thick, maybe a little more. I didn't allow for this thickness at the fold across the bottom. So, when I add the center divider, none of the edges line up any more. I trimmed some material off the bottom of the divider, that helped a little. I'm hoping I have enough material from the stitch line to the edges to be able to sand the edges fairly even.
So I called it done except for standing the edges, maybe wet molding some volume into it, and oiling/greasing the leather.
Next, and bigger, problem. I didn't want to fight sewing inside such a small pouch to attach the button after it is sewn together. So I marked out the hole, and the button placement and attached the button before assembling the pouch. Everything lines up nice, when it is flat.
But, when I put anything in it, even something as thin as my phone, the flap doesn't reach the button. I should have expected this, I usually make my shoulder slung pouches with an oversize flap because I have had this issue before. Not sure what I'll do to fix it. The button hole is too close to the flap edge to extend it down much. If I try to move the button up, I'll be left with two holes in the front of the bag.
Hopefully someone can learn from my mistakes. Luckily I would call this a "proof of concept" and can correct these issues on the next one.