Making a leather box-style bag (easy mode)

Pictured: hard mode. Do not try this at home

Bear with me, I'm figuring this out as I go.

The goal: make a rectangular prism tool bag, with zipper and handles. It should look pretty good and last forever. And not require a protractor or master's degree. Ideally, just a big rectangle of leather, one good needle + thread, and some scissors. And maybe a ruler (but not required).

1. Cut or obtain a rectangle of material. It will be about L+H on one side, and 2H+2W on the other.
2. Install the zipper, you now have a tube. Flip it inside out.
3. Sew the ends (Width in the middle of the ends of the "tube". (maybe attach a tab)
4. Cut out the 'corners', a two-layer square equal to Height/2
5. (maybe attach a handle) sew the remaining corners
6. Flip it rightside-out.
7. try to prevent your wife from stealing it.

The math is something like:

Seam allowance

some space between the stitch line and the edge of the material. 5mm is good.

stitch pitch

the space between stitches. 5mm is standard, this is defined by a tool / punch

Length

The desired overall length of the bag

Width

The desired overall width of the bag

Height

The desired overall height of the bag

The pattern is mostly a rectangle with 4 smaller rectangles cut out.

The big rectangle

(Length + Height) x (2*Width + 2*Height)

The zipper is installed the *entire* "Length" side and will, in total, be (Length + Height) long.

. Leave like an extra few cm on each side. Seriously consider butting the ends with some extra st

The corners

The "corners" are cut sorta on the middle of the (probably longer) sides of your material. From the edge, measure down (Height / 2 + Seam) to start the cut. Remove a rectangle (Height - 2*Seam) x (Height/2), 4 of these, each (Height / 2 + Seam) from the edge.

It might make sense to hold off cutting corners (ugh) until later.... especially if this is only the first 10 or so and you're not 100% on the pattern.

Lining

For tools you may want something inside the bag. Peel-and-stick Neoprene works really well. I don't know how well it holds up. Sunbrella or a canvas may also work, you'll want to use some sort of adhesive.

Sewing

Use double-sided tape. Install the zipper first. Consider extra material around the ends of the zipper for further support of the ends. Be sure the zipper is oriented correctly! Be sure the zipper part is installed and working in the teeth! This is your chance to get it right... Also be sure to cut the zipper a few cm long on both ends.

If lining (neoprene or otherwise) be sure to cover the zipper. IDEALLY, tape the zipper, then cover it with liner, then sew the zipper + liner together.

For better finish, try rolling the edge by the zipper. May require vv thin material idk.

Zip it together and flip the "tube" inside-out.

A pull tab

Install a small pull tab on the "open" end. This will push "inside" the bag, so when you flip it all right side-out the tab will hang off. This is SUPER USEFUL when pulling the zipper closed. If you're doing a handle on the closed side, you may not want a second tab.

Sew the matching longer edges together. If you haven't yet "cut corners", aim for the middle. The amount you sew will define the Width of the bag. FYI, the unsewn sides are 1/2 Height. Then ends (Width part) can be punched together to line 'em up better. Stitches are all hidden here, so lines aren't quite as picky.

Push the still inside-out bag into a sort of rectangle; the corners are still open. You'll have a seam allowance on the remaining corners, and they will mostly line up pretty straight.

Handle

If you want a handle on the end, insert it in this seam. I prefer one handle on the side where the zipper rests closed

Again, punch & stitch. Do your best but the stitches will be hidden so maybe don't freak out.